Encyclopedia of Farm Animal Nutrition

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					The Encyclopedia of Farm Animal Nutrition
         The Encyclopedia of
        Farm Animal Nutrition



                     Editor-in-chief

                      M.F. Fuller

          Rowett Research Institute, Aberdeen, UK



                      Section Editors

           N.J. Benevenga (Biochemistry)
           University of Wisconsin, Madison, USA


  M.F. Fuller (Non-ruminant Mammalian Nutrition)
          Rowett Research Institute, Aberdeen, UK


               S.P. Lall (Fish Nutrition)
      Institute for Marine Biosciences, Halifax, Canada


          K.J. McCracken (Avian Nutrition)
              Queen’s University, Belfast, UK

H.M. Omed and R.F.E. Axford (Ruminant Nutrition)
              University of Wales, Bangor, UK


C.J.C. Phillips (Nutritional Deficiencies and Disorders)
        University of Queensland, Gatton, Australia




                     CABI Publishing
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Library of Congress Cataloging-in-Publication Data
The encyclopedia of farm animal nutrition / editors, M.F. Fuller ... [et al.].
      p. cm.
   Includes bibliographical references.
   ISBN 0-85199-369-9 (alk. paper)
  1. Animal nutrition--Encyclopedias. 2. Animal feeding--Encyclopedias.
3. Feeds--Encyclopedias. I. Fuller, M. F. II. Title,
   SF94.65.E53 2004
   636.08 5 03--dc22
                                        2004002320
ISBN 0 85199 369 9


Typeset by Columns Design Ltd, Reading
Printed and bound in the UK by Biddles, King’s Lynn
                  Key to Contributors




AC     Alan Cembella          HFDeL   H.F. DeLuca
ADC    Anthony D. Care        IM      I. Murray
AJFR   A.J.F. Russel          JAM     J.A. Marlett
AJS    A.J. (Tony) Smith      JAMcL   John McLean
AM     Alan Morrow            JAP     James A. Pfister
BLS    Bryan L. Stegelmeier   JDO     John D. Olson
BMM    Bruce Moss             JDR     Jess Reed
CB     Carolyn Bird           JEM     Joyce Milley
CBC    Colin Cowey            JJR     J.J. Robinson
CJCP   Clive J.C. Phillips    JKM     Jean K. Margerison
CLA    Clare L. Adam          JMF     J.M. Forbes
CN     Cliff Nixey            JMW     J.M. Wilkinson
CRL    C.R. Lonsdale          JPG     J.P. Goff
DA     David Arney            JRS     J.R. Scaife
DCD    D.C. Deeming           JSA     Stewart Anderson
DD     David R. Davies        JSav    John Savory
DEC    Douglas Conklin        JSJr    Joseph Soares, Jr
DF     David Farrell          JvanM   Jaap van Milgen
DHB    David H. Baker         JW      Julian Wiseman
DJS    David J. Scarratt      JWS     John Suttie
DLF    David Frape            KDS     K.D. Sinclair
DLP    Donald L. Palmquist    KEP     Kip E. Panter
DMG    Delbert Gatlin, III    KF      Kieran Forbes
DMS    D.M. Schaefer          KJMcC   Kelvin J. McCracken
DN     Dominic Nanton         KP      Karin Pittman
DRG    Dale R. Gardner        LFJ     Lynn F. James
DS     David Speare           LR      L. Reynolds
EB     Elisabeth Baeza        MC-D    Margaret Clagett-Dame
ED     E. Deaville            MFF     Malcolm Fuller
EM     Erica Martin           MG      Mark Goodwill
EO     Emyr Owen              MHR     M.H. Ralphs
FLM    Fergus Mould           MMacL   Murdo Macleod
GG     Guy Groblewski         MMal    Mark Malpass

                                                              v
vi                         Key to Contributors




MMax   Martin Maxwell                 RMG        Rasanthi M. Gunasekera
MMit   Malcolm Mitchell               RNBK       R.N.B. Kay
NJB    N.J. Benevenga                 RSE        Rick Eisenstein
NS     Nick Sparks                    SAE        Sandra Edwards
PC     P.R. Cheeke                    SB         Sigurd Boisen
PCG    P.C. Garnsworthy               SC         Siphe Chikunya
PDL    Peter Lewis                    SEL        Stephen Lee
PGR    Philip G. Reeves               SPL        Santosh P. Lall
PJHB   P.J.H. Ball                    SPR        S. Paul Rose
RFEA   Roger F.E. Axford              TA         T. Acamovic
RG     Rob Gous                       TDC        T.D. Crenshaw
RGA    Robert G. Ackman               TS         Tim Smith
RH     Ronald Hardy                   VRF        Vernon Fowler
RHP    R. Peterson                    WKS        W. Kingsley Smith
RJ     Raymond Jones                  WRW        W.R. Ward
                                 Contributors




Acamovic, T., Avian Science Research Centre, SAC – Auchincruive, Ayr KA6 5HW, UK.
     acamovic@au.sac.ac.uk
Ackman, Robert G., Canadian Institute of Fisheries Technology, Dalhousie University, 1360
     Barrington Street, PO Box 1000, Halifax, Nova Scotia, Canada B3J 2X4. robert.ack-
     man@dal.ca
Adam, Clare L., Rowett Institute, Bucksburn, Aberdeen AB21 9SB, UK.
Anderson, Stewart, Global Marketing Manager Aquaculture, Roche Vitamins Ltd, Vitamins and
     Fine Chemicals Division, VMA Bldg 241/833, CH-4070 Basel, Switzerland.
     stewart.anderson@roche.com
Arney, David, Moulton College, West Street, Moulton, Northamptonshire NN3 7RR, UK.
Axford, Roger F.E., School of Agricultural and Forest Sciences, University of Wales, Bangor,
     Gwynedd LL57 2UW, UK.
Baeza, Elisabeth, Station de Recherches Avicoles, Centre INRA de Tours, 37380 Nouzilly,
     France. baeza@tours.inra.fr
Baker, David H., University of Illinois, 1207 W. Gregory Drive, Urbana, IL 61801, USA. d-
     baker1@uiuc.edu
Ball, P.J.H., 25 Sunningdale Avenue, Ayr KA7 4RQ, UK. peter@ball3636.freeserve.co.uk
Benevenga, N.J., University of Wisconsin, Madison, Department of Animal Sciences, 1675
     Observatory Drive, Madison, WI 53706-1284, USA. njbeneve@facstaff.wisc.edu
Bird, Carolyn, Institute for Marine Biosciences, National Research Council of Canada, 1411
     Oxford Street, Halifax, Canada B3H 3Z1.
Boisen, Sigurd, Research Centre Foulum, PO Box 50, 8830 Tjele, Denmark.
     sigurd.boisen@agrsci.dk
Care, Anthony D., Institute of Biological Sciences, University of Wales, Aberystwyth,
     Ceredigion SY23 3DD, UK.
Cembella, Alan, Pelagic Ecosystems Department, Marine Chemistry and Marine Natural
     Products, Am Handelshafen 12, D-27570 Bremerhaven (Building C-316), Germany.
     acembella@awi-bremerhaven.de
Cheeke, P.R., Oregon State University, Department of Animal Science, Withycombe 112,
     Corvallis, OR 97331, USA. peter.r.cheeke@orst.edu
Chikunya, Siphe, Writtle College, Chelmsford, Essex CM1 3RR, UK. sc@writtle.ac.uk
Clagett-Dame, Margaret, Department of Biochemistry, University of Wisconsin-Madison, 433
     Babcock Drive, Madison, WI 53706, USA. dame@biochem.wisc.edu

                                                                                         vii
viii                                     Contributors




Conklin, Douglas, Department of Animal Science, University of California, Davis, One Shields
     Avenue, Davis, CA 95616-8521, USA. deconklin@ucdavis.edu
Cowey, Colin, 5 Endrick Place, Aberdeen AB15 6EF, UK. ccowey@ifb.co.uk
Crenshaw, T.D., Department of Animal Sciences, University of Wisconsin-Madison, 1675
     Observatory Drive, Madison, WI 53706, USA. crenshaw@calshp.wisc.edu
Davies, David R., Plant Animal and Microbial Science, Institute of Grassland and Environmental
     Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK. david.davies@
     bbsrc.ac.uk
Deaville, E., Nutritional Sciences Research Unit, Department of Agriculture, School of
     Agriculture, Policy and Development, Earley Gate, PO Box 237, Reading RG6 6AR, UK.
     e.r.deaville@reading.ac.uk
Deeming, D.C., Hatchery Consulting and Research, 9 Eagle Drive, Welton, Lincolnshire LN2
     3LP, UK. charlie@deemingdc.freeserve.co.uk
DeLuca, H.F., Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock
     Drive, Madison, WI 53706, USA. deluca@biochem.wisc.edu
Edwards, Sandra, Department of Agriculture, University of Newcastle, King George VI
     Building, Newcastle upon Tyne NE1 7RU, UK. sandra.edwards@ncl.ac.uk
Eisenstein, Rick, Department of Nutritional Sciences, University of Wisconsin-Madison, 1415
     Linden Drive, Madison, WI 53706, USA. eisenste@nutrisci.wisc.edu
Farrell, David, 15 Bee St, Bardon, Queensland 4065, Australia. d.farrell@mailbox.uq.edu.au
Forbes, Kieran, Nutrition Services International, 211 Castle Road, Randalstown, BT41 2EB,
     UK.
Forbes, J.M., School of Biology, University of Leeds, Leeds LS2 9JT, UK. j.m.forbes@
     leeds.ac.uk
Fowler, Vernon, 1 Pittengullies Circle, Peterculter, Aberdeen, UK. vernonrfowler@aol.com
Frape, David, The Priory, Mildenhall, Suffolk IP28 7EE, UK. david.l.frape@btinternet.com
Fuller, Malcolm F., 107 Quaker Path, Stony Brook, NY 11790, USA. malcolm689@aol.com
Gardner, Dale R., USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT
     84341, USA.
Garnsworthy, P.C., School of Biosciences, University of Nottingham, Sutton Bonington,
     Loughborough, Leics LE12 5RD, UK. phil.garnsworthy@nottingham.ac.uk
Gatlin, Delbert, III, Department of Wildlife and Fisheries Sciences, Texas A&M University,
     2258 TAMUS, College Station, TX 77843-2258, USA. d-gatlin@tamu.edu
Goff, J.P., USDA – Agricultural Research Service, National Animal Disease Center, Ames,
     IA 50010, USA.
Goodwill, Mark, Harbro Farm Sales Ltd, Tore Mill, Harbour Road, Inverness IV2 1UA, UK.
     mark.goodwill@harbro.co.uk
Gous, Rob, University of Natal, Post Bag X01, Scottsville 3209, South Africa. gous@nu.ac.za
Groblewski, Guy, Department of Nutritional Sciences, University of Wisconsin-Madison, 1415
     Linden Drive, Madison, WI 53706, USA. groby@nutrisci.wisc.edu
Gunasekera, Rasanthi M., School of Ecology and Environment, Deakin University, PO Box
     423, Warrnambool, Victoria 3280, Australia. rasanthig@hotmail.com
Hardy, Ronald, Director, Hagerman Fish Culture Experimental Station, 3059F National Fish
     Hatchery Road, Hagerman, ID 83332, USA. rhardy@micron.net
James, Lynn F., USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT
     84341, USA.
Jones, Raymond, Forage Conservation and Utilisation, Institute of Grassland and
     Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK,
     raymond.jones@bbsrc.ac.uk
Kay, R.N.B., 386 North Deeside Road, Cults, Aberdeen AB15 9SS, UK.
Lall, Santosh P., Institute for Marine Biosciences, National Research Council of Canada, 1411
     Oxford Street, Halifax, NS, Canada B3M 3Z1. santosh.lall@nrc-cnrc.gc.ca
                                         Contributors                                       ix




Lee, Stephen, USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT 84341,
      USA.
Lewis, Peter, Northcot, Cowdown Lane, Goodworth Clatford, Andover, Hants SP11 7HG, UK.
      peter.lewis@dsl.pipex.com
Lonsdale, C.R., 11 North Field Way, Appleton, Roebuck, Yorkshire YO5 7EA, UK.
      lonsdale@btconnect.com
Macleod, Murdo, Division of Integrative Biology, Roslin Institute (Edinburgh), Midlothian EH25
      9PS, UK. murdo.macleod@bbsrc.ac.uk
Malpass, Mark, 106 Kings Court, Ramsey, Isle of Man IM8 1LJ, UK.
Margerison, Jean K., Seale-Hayne Faculty of Agriculture, Food and Land Use, University of
      Plymouth, Newton Abbot, Devon TQ12 6NQ, UK. j.margerison@plymouth.ac.uk
Marlett, J.A., Department of Nutritional Sciences, University of Wisconsin-Madison, 1415
      Linden Drive, Madison, WI 53706, USA. jmarlett@nutrisci.wisc.edu
Martin, Erica, Harper Adams University College, Newport, Shropshire TF10 8NB, UK.
      emartin@harper-adams.ac.uk
Maxwell, Martin, 15 Orchard Road, Edinburgh, EH4 2EP, UK. maxwellmh@aol.com
McCracken, Kelvin J., Department of Agricultural and Environmental Science, Agriculture and
      Food Science Centre, Queen’s University, Newforge Lane, Belfast BT9 5PX, Northern
      Ireland. kelvin@mccracken2058.fslife.co.uk
McLean, John, 124 Bentinck Drive, Troon, Ayrshire KA10 6JB, UK. jmclean@bentinck
      124.fsnet.co.uk
Milley, Joyce, Institute for Marine Biosciences, National Research Council of Canada, 1411
      Oxford Street, Halifax, Canada B3H 3Z1. joyce.milley@nrc-cnrc.gc.ca
Mitchell, Malcolm, Roslin Institute (Edinburgh), Roslin, Midlothian EH25 9PS, UK.
      malcolm.mitchell@bbsra.ac.uk
Morrow, Alan, ABNA Ltd, PO Box 250, Oundle Road, Peterborough PE2 9QF, UK. amor-
      row@abn.co.uk
Moss, Bruce, Food Science Division, Dept of Agriculture and Rural Development, Newforge
      Lane, Belfast BT9 5PX, Northern Ireland.
Mould, Fergus, Department of Agriculture, University of Reading, Earley Gate, PO Box 236,
      Reading RG6 2AT, UK.
Murray, I., SAC – Aberdeen, Ferguson Building, Craibstone, Bucksburn, Aberdeen AB21 9YA,
      UK. i.murray@ab.sac.ac.uk
Nanton, Dominic, Institute for Marine Biosciences, National Research Council of Canada,
      1411 Oxford Street, Halifax, Canada B3H 3Z1. dominic.nanton@nrc-cnrc.gc.ca
Nixey, Cliff, British United Turkeys Ltd, Hockenhull Hall, Tarvin, Chester, Cheshire CH3 8LU,
      UK. cliff.nixey@merial.com
Olson, John D., USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT
      84341, USA.
Owen, Emyr, Department of Agriculture, University of Reading, Earley Gate, PO Box 236,
      Reading RG6 2AT, UK. emyrowen@ukonline.co.uk
Palmquist, Donald L., Department of Animal Sciences, OARDC/OSU, 1680 Madison Ave.,
      Wooster, OH 44691, USA. palmquist.1@osu.edu
Panter, Kip E., USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT
      84341, USA.
Peterson, R.N.B., Biological Station, Department of Fisheries and Oceans, St Andrews, New
      Brunswick, Canada E5B 2L9. petersonr@mar.dfo-mpo.gc.ca
Pfister, James A., USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT
      84341, USA.
Phillips, Clive J.C., University of Queensland, School of Veterinary Sciences, Gatton Campus,
      Gatton, Queensland 4343, Australia. c.phillips@uq.edu.au
x                                        Contributors




Pittman, Karin, Department of Fisheries and Marine Biology, University of Bergen, Bergen
     5020, Norway. karin.pittman@ifm.uib.no
Ralphs, M.H., USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT 84341,
     USA. mralphs@cc.usu.edu
Reed, Jess, Department of Animal Sciences, University of Wisconsin-Madison, 1675
     Observatory Drive, Madison, WI 53706, USA. reed@calshp.cals.wisc.edu
Reeves, Philip G., USDA, ARS, Grand Forks Human Nutrition Research Center, 2420 2nd
     Avenue North, Grand Forks, ND 58203, USA. preeves@gfhnrc.ars.usda.gov
Reynolds, L., Manor Farmhouse, Huish Champflower, Taunton, Somerset TA4 2EY, UK.
     reynoldslen@aol.com
Robinson, J.J., Scottish Agricultural College, Animal Biology Division, Ferguson Building,
     Craibstone Estate, Bucksburn, Aberdeen AB2 9YA, UK. j.robinson@ab.sac.ac.uk
Rose, S. Paul, Harper Adams Agricultural College, Edgmond, Newport, Shropshire TF10 8NB,
     UK. sprose@harper-adams.ac.uk
Russel, A.J.F., Newton Bank, Frankscroft, Peebles EH45 9DX, UK. ajfrussel@aol.com
Savory, John, National Centre for Poultry Studies, Scottish Agricultural College, Auchincruive,
     Ayr, KA6 5HW, UK. j.savory@au.sac.ac.uk
Scaife, J.R., Department of Agriculture, University of Aberdeen, 581 King Street, Aberdeen
     AB24 5UA, UK. j.r.scaife@abdn.ac.uk
Scarratt, David J., RR No. 3, Bridgetown, Nova Scotia, Canada B0S 1C0. scarratt@
     ns.sympatico.ca
Schaefer, D.M., Animal Sciences Department, University of Wisconsin-Madison, 1675
     Observatory Drive, Madison, WI 53706-1284, USA. schaeferd@ansci.wisc.edu
Sinclair, K.D., School of Biosciences, University of Nottingham, Sutton Bonington Campus
     Leicestershire LE12 5RD, UK. kevin.sinclair@nottingham.ac.uk
Smith, A.J. (Tony), CTVM, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25
     9RG, UK. anthony.smith@talk21.com
Smith, W. Kingsley, Nuffield House, 61A Cowley Drive, Cambridge, New Zealand.
     kingsley@wave.co.nz
Smith, Tim, 27 Marlborough Avenue, Reading RG1 5JB, UK.
Soares, Joseph, Jr, University of Maryland, 2131 Animal Sciences Center, College Park, MD
     20742, USA. js89@umail.umd.edu
Sparks, Nick, Avian Science Research Centre, Auchincruive, Ayr KA6 5HW, UK.
     n.sparks@au.sac.ac.uk
Speare, David, Fish Pathology Department, Atlantic Veterinary College, University of Prince
     Edward Island, Charlottetown, PEI, Canada C1A 4P3. speare@upei.ca
Stegelmeier, Bryan L., USDA/ARS Poisonous Plant Laboratory, 1150 E. 1400 N., Logan, UT
     84341, USA.
Suttie, John, Department of Biochemistry, University of Wisconsin-Madison, 420 Henry Mall,
     Madison, WI 53076, USA. suttie@biochem.wisc.edu
van Milgen, Jaap, Station de Recherches Porcines, Institut National de la Recherche
     Agronomique, 35590 St Gilles, France. jaap.vanmilgen@rennes.inra.fr
Ward, W.R., Department of Veterinary Clinical Science, University of Liverpool, Neston, Wirral
     L64 7TE, UK.
Wilkinson, J.M., Centre for Animal Sciences, Leeds Institute for Plant Biotechnology and
     Agriculture, Irene Manton Building, University of Leeds, Leeds LS2 9JT, UK. j.m.wilkin-
     son@leeds.ac.uk
Wiseman, Julian, Department of Agriculture and Horticulture, Sutton Bonington Campus,
     Loughborough LE12 5RD, UK. julian.wiseman@nottingham.ac.uk
                                     Preface




An encyclopedia should properly encompass the totality of human knowledge, or
at least of some particular sector of it. Not so many years ago it would have been
possible to contain all that was known of animal nutrition in a book the size of this,
for the science of nutrition is young, but such has been the pace of its growth that
that is no longer possible. The nutrition of farm animals is a complex subject, reach-
ing into biochemistry, physiology, pathology, veterinary medicine, animal hus-
bandry and agriculture and even, as evidenced in the following pages, beyond
those disciplines. The subject matter of farm animal nutrition is covered in a large
number of text books – most are referred to in the entries of this encyclopedia – but
their arrangement does not lend itself to the rapid recovery of specific pieces of fac-
tual information and it was with that object in view that this encyclopedia was
devised and written. Its aims are completeness, accuracy, succinctness and ease of
access. The aim of completeness – to include as much factual information as possi-
ble – was addressed by embracing all the ramifications of nutrition just mentioned.
Yet, no doubt there are omissions. To achieve a high degree of accuracy authors
were chosen for their expertise in specialized areas of nutrition. But mistakes there
surely are and for those that I have failed to spot I would plead, as that pioneer lexi-
cographer Dr Johnson famously pleaded, when asked by a lady why he had defined
‘pastern’ as ‘the knee of a horse’, ‘Ignorance, Madam, pure ignorance’. To encom-
pass the whole of farm animal nutrition in this space obviously requires succinct-
ness and all the contributors were enjoined to be as brief as possible – though some
found it harder than others. Finally, ease of access is ensured by the alphabetical
arrangement of the entries and the system of cross-references. There is more on this
in the note that follows.
   Although there have been other encyclopedias of nutrition they have been more
in the nature of collections of review articles, valuable certainly, but not providing
the ready access to specific facts and figures that is the essence of this work. This is
the first encyclopedia to be devoted exclusively to the nutrition of farmed animals,
including birds and fish. It contains some 2000 entries, written by about 100 special-
ists and reviewed by an international editorial panel. The entries range from short

                                                                                      xi
xii                                    Preface




definitions of terms to extended descriptions of subjects of major importance. The
entries are illustrated by figures (e.g. chemical structure, anatomy, graphs), tables
(e.g. families of nutrients, feed composition) and photographs (of things that can
best be appreciated visually). Entries are supported by references to important orig-
inal papers and reviews, with suggestions for further reading. The encyclopedia
includes definitions of terms commonly used in nutrition; chemical structures and
functions of nutrients, important metabolites, toxins, etc.; explanations of nutri-
tional processes; their physiological and metabolic bases; descriptions of the major
farmed species, their metabolism and practical feeding; composition and nutritional
value of important crops and feedstuffs; feed processing; feeding systems. It is
intended as a book that users will regularly refer to for information because they
know it will be there.
   Because this is the first time that such an encyclopedia has been published, it
must also be seen as a work in evolution, not yet complete. To further its evolution,
so that future editions can be more nearly complete, more accurate and more infor-
mative, readers are invited, and requested, to submit their suggestions for amend-
ments. Just as the first editor of the Oxford English Dictionary relied upon a host of
contributors to submit material, it seems appropriate to ask the readers of this vol-
ume, some of whom undoubtedly have specialized knowledge, to contribute, if
they will be so kind. Suggested amendments should be addressed to the Editor-in-
chief, care of the publisher.
   This book represents the combined efforts of many people and I would like to
thank, first, the authors, who have distilled their many years of learning into a very
few words. I owe a great debt of gratitude to my fellow editors who have not only
secured the services of the many contributors but helped me to edit the resulting
writing so as to achieve some kind of uniformity of presentation. In addition to the
editors whose names are on the title page, I am most grateful to those who, for vari-
ous reasons, were unable to complete their roles; to the late Dr John Topps, to Dr
Angus Russell, Dr Colin Fisher and Dr Julian Wiseman.
   I wish to express particular appreciation to Rebecca Stubbs, Development Editor
(Books and Reference Works) at CAB International. Her patience in the face of
numerous delays and her helpfulness have made an enjoyable experience of what
could have been an irksome chore. I am also most grateful to Sarah Williams for her
careful work on the manuscript and to Rachel Robinson for production. Finally, I
thank my wife Margaret for her tolerance of all the hours in which I have neglected
her, the house and the garden.
                                                                     Malcolm Fuller
                                                               Stony Brook, New York
                                                                      September 2003
             Notes on Using the Encyclopedia




The entries are in alphabetical order, using English, not American, spelling. Where
there are two or more names for the same subject, the entry appears under the most
common name, alternative names appearing as blind entries, directing the reader to
the common name under which the entry appears. For example ‘Gossypose: see
Raffinose’.
   Within an entry, a bold typeface highlights a word that is an entry in its own right.
For example, in the entry ‘calorimetry’ the passage ‘Distinction must be made
between direct calorimetry, which is the physical measurement of heat given off by
the animal, and indirect calorimetry, in which the measurements are of the chemi-
cal quantities involved in metabolism … ’ indicates that there are also entries on direct
calorimetry and indirect calorimetry.
   Where information related to the content of an entry is to be found elsewhere, but
where the cross-reference is not indicated by a highlighted word in the text, there may
be a footnote beginning ‘See also’ to direct the reader to that other material. For
example, the entry ‘absorption’ does not contain the word ‘digestion’ but the entry
‘digestion’ nevertheless includes information on absorption.




                                                                                      xiii
                                              A

Abalone         A large marine snail or gastro-    chemical and physical nature can vary
pod of the family of molluscs Haliotidae. More     between species, reflecting not only genetic
than 50 species have been identified. Abalone       traits but also diet. For example, abdominal
have a hard shell and a muscular foot. They        deposits of fat in horses and certain Channel
inhabit rocky shorelines, from shallow water       Island breeds of cattle are yellow while those
up to depths of approximately 40 m. Their          of sheep are hard and white and those of pigs
shells are rounded or oval with a large dome       soft and greyish in colour. Body temperature
towards one end. The shell has a row of respi-     is important, with fat being almost semi-fluid
ratory pores. The muscular foot has strong         compared with that at cooler temperatures.
suction power, permitting the abalone to           Brown adipose tissue is not found in abdomi-
clamp tightly to rocky surfaces.                   nal fat stores.                        (MMax)
    Abalones have succulent meaty bodies with
a delicious flavour, placing them in high           Abomasum           The fourth compartment
demand in Japan, China and other Asian             of the ruminant stomach. It communicates
countries. With their capture fisheries in seri-    anteriorly with the omasum through the
ous decline, abalone farming is expanding in       omaso-abomasal opening, and posteriorly
Taiwan, Chile, Iceland, Mexico, USA, Aus-          with the duodenum via the pyloric orifice.
tralia, Thailand and several countries in          Like the stomach of non-ruminants, it is lined
South-east Asia; however, South Africa is the      with a glandular epithelium that secretes
world’s largest producer of cultured abalone.      mucus, hydrochloric acid and proteolytic
In the natural environment abalone graze on        enzymes.                             (RNBK)
benthic (bottom-growing) algae, but formu-
lated diets from a combination of animal and       Abortion          Abortion is defined relative to
plant protein sources have been developed for      the stage of pregnancy when the embryo or
feeding farmed abalone.                   (SPL)    fetus is lost. In cattle, early embryonic death
                                                   refers to deaths occurring from the day of
Abdominal fat            In most domesticated      conception until about 42 days of gestation
species, deposits of abdominal fat can be          (the end of the embryonic period), which coin-
divided between peritoneal and inguinal            cides with the end of differentiation. Embryos
regions; the exception is the duck, in which       lost during this period may be either resorbed
subcutaneous fat deposits, required for ther-      or aborted. A normal rate of early embryo
mal insulation, comprise the largest single        resorption (0–45 days) is 9–12% and abortion
depot and are a special development in this        or resorption after 45–60 days is usually rare
species. The fat of the peritoneum is located      (1–2%). Higher rates are attributed to disease.
within the abdominal cavity and extends ven-       Bovine fetuses discharged from day 42 until
trally over the visceral mass, being attached to   approximately 260 days are generally called
the peritoneal membranes lining the abdomi-        abortions, and from day 260 until normal
nal wall. Inguinal fat lies along the interior     term (281 ± 3 days), premature births.
femoral and tibiotarsal region and extends             Dietary causes of embryonic death, abor-
from the sartorious muscle to approximately        tion or premature birth include poisonous
two-thirds the length of the tibiotarsus. Con-     plants, fungi and synthetic toxicants. Plants
sistency and appearance of fat in terms of its     associated with abortion or premature birth


                                                                                                 1
2                                           Absorption




include Pinus species (P. ponderosa, P. radi-         Absorption of macromolecules can occur
ata, P. taeda, P. cubensis), Juniperus com-        in specific instances; for example, absorption
munis, cypress (Cupressus macrocarpa),             of immunoglobulins from colostrum in new-
snakeweeds (Gutierrezia sarothrae and G.           born mammals is performed by pinocytosis,
microcephala), locoweeds (Astragalus spp.          mainly in the ileum.
and Oxytropis spp. containing swainsonine),           Absorption of some minerals and of degra-
hairy vetch (Vicia villosa), darling pea in Aus-   dation products from microbial fermentation,
tralia (Swainsona spp.) and leucaena (Leu-         such as short-chain fatty acids (SCFA), also
caena leucocephala). Mycotoxins include            takes place in the large intestine. In the horse,
ergot alkaloids from grains and grasses            up to 70% of the absorbed energy is absorbed
infected with Claviceps and Balansia spp.,         as SCFA in the colon. In ruminants, absorp-
loline alkaloids from endophyte-infected tall      tion of these products mainly takes place in
fescue, trichothecenes from Fusarium spp.,         the fore-stomach.
grains and maize silage infected with                 Little water is absorbed from the stomach,
Aspergillus and Penicillium spp. and hay           but it moves freely across the mucosa in both
                                                   directions in the small intestine and large
and straw and mouldy sweet clover
                                                   intestine and generally the osmolality in the
(dicoumarol) contaminated with Stachybotrys
                                                   intestinal lumen is close to that of plasma. In
spp. Xenobiotics believed to contribute to
                                                   the colon, sodium is pumped out and water
embryo or fetal loss include nitrates and
                                                   moves passively with it.                     (SB)
nitrites, high-protein diets (excess urea), car-
                                                   See also: Digestion; Intestinal absorption
bon monoxide, oestrogenic compounds, glu-
cocorticoids, lead, phenothiazines, oxytocin,
                                                   Acceptability: see Palatability
chlorinated pesticides (DDT, dieldrin, hep-
tachlor) and warfarin (coumarins).         (KEP)
                                                   Acetaldehyde           An aldehyde, CH3·CHO.
                                                   It can be produced chemically by oxidation of
Absorption           The process by which
                                                   ethanol CH3·CH2OH. In cellular metabolism,
nutrients are transported from the lumen of        acetaldehyde is an intermediate produced in
the gastrointestinal tract to the blood or lym-    the conversion of ethanol to acetic acid. After
phatic system. Absorption of most nutrients        activation in the cell, acetic acid can be used
occurs predominantly in the jejunum.               as a source of energy. Acetaldehyde can be
Absorption of intact macromolecules is very        toxic.                                    (NJB)
limited. Most are degraded into their con-
stituents by digestive enzymes in the intestinal   Acetate         CH3·COO–.          Acetic    acid,
lumen: proteins to amino acids and small           CH3·COOH, is one of the three (acetic, propi-
oligopeptides; glycogen to maltose, isomal-        onic, butyric) common short-chain volatile fatty
tose and small oligosaccharides; triglycerides     acids found in intestinal contents. This fatty
to fatty acids, 2-monoglycerides and glycerol.     acid accounts for a major proportion (more
Further degradation of proteins and carbohy-       than half) of the short-chain fatty acids pro-
drates occurs at the brush border surface          duced by anaerobic fermentation in the rumen
under the influence of a large number of spe-       or in the large intestine. In cellular metabolism,
cific enzymes for degradation to their mono-        acetate is converted to acetyl-coenzyme A
constituents, amino acids (small amounts of        (CoA) prior to being used in catabolic or ana-
peptides may pass to the blood) and the hex-       bolic processes. Acetyl-CoA is a major meta-
oses glucose, fructose and galactose (fructose     bolic intermediate in the catabolism of fatty
is converted to glucose in the intestinal cells    acids and carbohydrates to carbon dioxide and
before being transferred to the blood). Degra-     water and of amino acids to carbon dioxide,
dation products from lipids are emulsified by       water and nitrogen end products in the pro-
bile salts and lecithin and organized in           duction of the cellular energy in the form of
micelles which diffuse through the unstirred       ATP. In cellular biosynthetic activities, acetate
water layer to the membrane of the brush bor-      as acetyl-CoA is the precursor for all of the
der, where the components are absorbed             carbon in long-chain fatty acids (16–18 car-
except the bile salts.                             bons), ketones and cholesterol.             (NJB)
                                      Acid–base equilibrium                                      3




Acetic acid: see Acetate                           tion, severe diarrhoea, asphyxia, ketosis and
                                                   lactic acidosis. Alkalosis is defined as a blood
Acetoacetate            CH 3 ·CO·CH 2 ·COO – ,     pH > 7.45 and is associated with hyperventi-
one of the three ketone bodies (acetoacetate,      lation, vomiting of gastric acid and diuresis.
β-hydroxybutyrate and acetone) produced in         Three systems within the body are primarily
the incomplete oxidation of fatty acids. In the    responsible for maintenance and regulation of
liver, fatty acids, via their metabolism to        acid–base equilibrium. These are the physio-
acetyl-coenzyme A, can produce acetoacetyl-        logical buffers, the respiratory system and the
coenzyme A which in turn can be converted          renal system. These systems are interrelated
to the other two ketone bodies. Acetoacetate       and provide relatively rapid responses to shifts
and β-hydroxybutyrate can be taken up by           in acid–base equilibrium. The gastrointestinal
other tissues and used for energy.        (NJB)    tract also plays important roles in acid–base
                                                   equilibrium but the responses are of greater
Acetone          CH3·CO·CH3, one of the            consequence to long-term regulation and
three ketone bodies (acetoacetate, β-hydroxy-      involve shifts in absorption and excretion of
butyrate and acetone) produced in the incom-       mineral ions.
plete oxidation of fatty acids. Because acetone        Major physiological buffers include bicar-
is volatile and has a unique sweet odour, it can   bonate, phosphate and proteins. Bicarbonate
sometimes be detected in the breath of ketotic     ions (HCO3–) and hydrogen ions (H+) are in
animals. Acetone is not further metabolized        equilibrium with carbonic acid (H2CO3), a
and is lost from the animal.              (NJB)    weak acid. Carbonic acid is produced by enzy-
                                                   matic action of carbonic anhydrase from CO2
Acetyl-CoA          Acetyl    coenzyme      A,     and H2O. The formation and end-products of
CH3·CO·SCoA, is the metabolically active           bicarbonate can be easily eliminated via respi-
form of acetate. It is produced in the metabo-     ratory or renal systems without an effect on
lism of carbohydrates, fatty acids and some        pH. Since mechanisms exist to maintain a
amino acids. Free acetate is converted to          constant extracellular concentration of bicar-
acetyl-CoA in the cytoplasm of cells and uti-      bonate ions (which are an excellent buffer for
lizes coenzyme A and ATP in its production.        physiological fluids), the bicarbonate buffer
(NJB)                                              does not provide a means for net elimination
                                                   of acidic or basic loads imposed on the body.
Acetylcholine              A neurotransmitter,     In terms of acid–base equilibrium, the bicar-
(CH3)3N+·CH2·CH2OOC·CH3. It is formed in           bonate buffer is considered a futile cycle since
nerve endings by combining acetyl-CoA with         net elimination of bicarbonate as CO2 via the
choline and is found in synaptic vesicles.         lungs is eventually compensated for by renal
These vesicles are released into the synapse in    synthesis of bicarbonate by the kidneys with
response to nerve impulses and initiate a          no net change in H+. Phosphate ions buffer
response in another nerve or muscle.     (NJB)     H+ in physiological fluids and contribute to the
                                                   net equilibrium of acids and bases in the body.
Acid–base equilibrium            The balance       Within physiological pH ranges the concen-
between acids (elements or compounds that          tration of dibasic (HPO4–) phosphate ions is
increase H+ concentration) and bases (ele-         approximately four times the concentration of
ments or compounds that decrease H+ con-           monobasic (H2PO4–), but the kidneys can con-
centration). Neutrality (equal balance of acid     centrate H+ in urine to a pH as low as 4.5. As
and base) is at a pH of 7.0 (H+ concentration      urine pH decreases, the dibasic phosphate
= 1     10 7 mol l 1). However, homeostatic        ions provide a buffer by accepting H+ to form
mechanisms in living organisms tend to main-       monobasic phosphate, thus providing net
tain an extracellular fluid pH between 7.35         elimination of H+ from the body.
and 7.45. Survival of the organism is not pos-         Another major route for a net elimination
sible outside of the range of a pH between         of H+ from the body involves renal production
7.0 and 7.7. Acidosis is defined as a blood         and secretion of ammonium ions from gluta-
pH < 7.35 and occurs with prolonged starva-        mine catabolism. Under acid loads a trans-
4                                              Acid-detergent fibre




porter in renal mitochondria is inhibited,                  References and further reading
resulting in additional degradation of gluta-               Goering, H.K. and Van Soest, P.J. (1970) Forage
mine and excretion of H+ as ammonium                           Fibre Analysis. Agriculture Handbook No. 379,
(NH4+).                                                        US Department of Agriculture, Washington,
                                                               DC.
   The strong ion difference (SID), which is
                                                            Southgate, D.A.T. (1991) Determination of Food
the sum of all strong cations (mol l 1) minus
                                                               Carbohydrates, 2nd edn. Elsevier.
the sum of all strong anions (mol l 1), also                Van Soest, P.J. (1967) Development of a compre-
impacts on the regulation of acid–base equilib-                hensive system of feed analyses and its applica-
rium. The SID affects the partial pressure of                  tion to forage. Journal of Animal Science 26,
blood CO2 and renal electrolyte excretion.                     119.
Shifts in SID impact renal compensation by                  Van Soest, P.J. and Wine, R.H. (1967) Use of
changes in the relative amounts of ammonium                    detergents in the analysis of fibrous feeds. IV.
and phosphate ion excretion.            (TDC)                  Determination of plant cell wall constituents.
                                                               Journal of Association of Official Analytical
                                                               Chemists 50, 50–55.
Acid-detergent         fibre    (ADF)          The
                                                            Van Soest, P.J. and Wine, R.H. (1968) Determina-
detergent fibre analysis scheme was intro-
                                                               tion of lignin and cellulose in Acid Detergent
duced to overcome inadequacies in the use of                   Fibre with permanganate. Journal of Associa-
the traditional acid–alkali crude fibre estima-                 tion of Official Analytical Chemists 51,
tion when applied to fibrous forage feeds for                   780–785.
ruminants (Van Soest, 1970; see table).
   The determination of ADF involves the                    Acid-detergent fibre nitrogen (ADFN)
extraction of food (1 g) by boiling (1 h) in acid-          The amount of nitrogen retained in the acid-
detergent solution (100 ml; 2% cetyltrimethyl-              detergent fibre residue. Also called acid-
ammonium bromide (CTAB) in 0.5 M                            detergent insoluble nitrogen (ADIN), it has
H2SO4). The insoluble residue is filtered,                   been used to determine heat damage to pro-
washed with acetone, dried (8 h, 100°C) and                 teins in feedstuffs. Excessive heating of
weighed. This residue, which includes cellu-                foods containing protein and carbohydrate
lose, lignin and some inorganic elements such               leads to Maillard reactions which cause the
as silica, is described as ADF. The residue can             formation of covalent bonds between alde-
be used for subsequent measurement of cellu-                hyde groups in carbohydrate and free amino
lose after oxidation of lignin by saturated                 group residues on protein, especially lysine.
potassium permanganate solution and                         ADFN is an indicator of these heating
removal of manganese dioxide by oxalic acid                 effects, which decrease the digestibility of
(Van Soest and Wine, 1968).                   (IM)          the protein.                             (IM)


Classification of forage fractions using the detergent fibre methods of Van Soest (1967).

Fraction                                                  Components

Cell contents (soluble in                                 Lipids
  neutral detergent                                       Sugars, organic acids and water-soluble matter
                                                          Pectin, starch
                                                          Non-protein N
                                                          Soluble protein
Cell wall constituents (fibre insoluble in
  neutral detergent)
  1. Soluble in acid detergent                            Hemicelluloses
                                                          Fibre-bound protein
    2. Acid-detergent fibre                                Cellulose
                                                          Lignin
                                                          Lignified N
                                                          Silica
                                   Acidity of the gastrointestinal tract                             5




Acid treatment              Acids are generally        fermentation. A.I. Virtanen of Finland first
applied to forages either to improve the               developed the use of acids in this way in the
degradability of poor quality cereal crop              1930s. In what became known as the AIV
residues or to enhance pH reduction during             method, combinations of sulphuric and
ensiling. They are also used as dietary supple-        hydrochloric acids were added to forages at
ments to help maintain blood pH. The addi-             ensiling to encourage the rapid reduction of
tion of either hydrochloric or sulphuric acid to       pH (< 4) so as to suppress proteolytic activity.
cereal straws reduces hemicellulose content            A number of acid-based silage additives are
but has little effect on either cellulose or           now available. For safety and to limit their
lignin. However, digestibility and intake              corrosive effect, weaker organic acids such as
improve and so, like alkali treatment, acid            formic acid are used, either alone or in combi-
treatment may hydrolyse the ester bonds                nation with fermentation inhibitors such as
between lignin and the other cell wall polysac-        formalin. The application of acids has been
charides. Again like alkali treatment, acid            shown to increase animal performance, due
treatment improves degradability, but suffi-            to reduced losses of nutrients as well as
cient dietary protein must be supplied to              improved protein quality, palatability and
ensure that this potential can be realized. Ani-       intake.                                   (FLM)
mals consuming cereal straw treated with acid
and urea have been shown to have both an               Acidification          Acids are sometimes
enhanced flow of microbial protein to the               added to animal feed ingredients or diets to
small intestine and increased nitrogen reten-          protect the material against microbial deterio-
tion. An additional benefit identified with this         ration or to reduce the pH in the animal’s
combined treatment is that acidification                stomach. Propionic acid can be added to hay
appears to enhance the degree of ammonia-              or cereal grains to prevent the growth of
tion of straw by the urea. When sulphuric acid         moulds and the formation of mycotoxins. This
is used, the sulphur content of the treated            allows such feed materials to be stored safely
material increases, which may be beneficial as          with a higher moisture content than is nor-
sulphur is a vital element in the production of        mally recommended. Short-chain organic
microbial protein. It is generally recom-              acids (e.g. formic, propionic, fumaric and cit-
mended that where additional nitrogen is sup-          ric) can be added to diets for newly weaned
plied, sulphur should be provided at a ratio of        piglets to reduce digestive upsets. The young
S:N of about 1:12. Short-term treatment of             piglet has an immature gut, where enzymatic
cereal straw with organic acids such as formic         activity and hydrochloric acid secretion are
acid have no effect on either digestibility or         not sufficiently developed; piglet feeds often
intake, with the acids being degraded in the           have a high acid-binding capacity and are fed
rumen to methane and carbon dioxide.                   in relatively large meals. Organic acids reduce
    The most common use of acids is their              the incidence of diarrhoea in piglets by their
incorporation into the herbage mass to                 antimicrobial action on the feed itself, by
enhance the rate of pH reduction during ensil-         reducing stomach pH and by acting as energy
ing. Successful preservation of plant material         sources. Lactic acid can be added to dried
as silage depends on rapidly achieving a con-          milk powder for artificial rearing of calves.
trolled fermentation under anaerobic condi-            Lactic acid preserves reconstituted milk, allow-
tions and the conversion of water-soluble              ing ad libitum feeding of cold milk; it also
carbohydrates to lactic acid. At pH 3.8 to             reduces the pH of the calf’s abomasum,
4.3, microbial activity is inhibited, resulting in     thereby assisting clot formation.         (PCG)
well-preserved, stable silage. When the crop
and conditions within the silo permit, no addi-        Acidity of the gastrointestinal tract
tives are needed; but where either these are           The quality of being acid describes a solution
inadequate or to minimize losses in fermenta-          with a pH less than 7.0. The contents of the
tion, the desired pH can be partly achieved by         stomach or abomasum are normally acid
direct acidification. This promotes a lactic acid       because of the secretion of 0.15 M hydrochlo-
fermentation and lowers the energy cost of             ric acid by the parietal cells in the gastric
6                                            Acidosis




mucosa. This acid is bacteriocidal for many        ment backbone and combines with myosin to
ingested organisms; it also provides the neces-    produce muscle contraction in the presence of
sary pH for the conversion of pepsinogen to        adenosine triphosphate (ATP). Actin is the
pepsin and for the latter to start the digestion   second most abundant protein in muscle,
of dietary protein. The gastric mucosa is pro-     making up 10% of the total protein.     (NJB)
tected from self-digestion by an unstirred layer
of mucus, made alkaline with bicarbonate.
    Because of its high content of bicarbonate,
the pancreatic juice secreted into the duode-
num is alkaline, e.g. pH 8.0. In addition, bile
and intestinal juice both tend to be alkaline
and so these three secretions soon neutralize
the gastric contents entering the duodenum
and raise the pH of the duodenal contents to
6.0–7.0. By the time the chyme reaches the         The arrangement of actin, tropomyosin and troponin
jejunum, its reaction is neutral or may become     in the thin filament.
alkaline, depending on the species. This has
an important bearing on the solubility of cal-     Activity, of enzymes: see Enzyme activity
cium phosphate and the absorption of cal-
cium ions from the upper part of the small         Activity, physical          Activity is brought
intestine (see Hyperparathyroidism).               about by muscular contractions in which
    The pH of the contents of the large intes-     chemical energy stores are converted into
tine is close to neutrality; however, in the       mechanical energy, which in turn is converted
horse, and other species in which there is a       into heat as the work is performed. In this
good deal of cellulose fermentation in the cae-    sense it is wasted energy but some activity is
cum and colon with the production of volatile      essential – for example, foraging by free-
fatty acids, the pH of the gut contents in these   range animals, which involves further energy
regions is nearer 6.0 than 7.0.           (ADC)    expenditure. This has led to the development
                                                   of intensive production systems for egg layers
Acidosis: see Lactic acidosis                      and for growing chickens, pigs and calves,
                                                   where activity is minimized.
Acorn          The fruit of the oak tree (Quer-        Although chemical energy can be mobi-
cus spp.). Acorns can be dehulled but are          lized very quickly for vigorous work, this may
more frequently fed whole as, for example, to      not be reflected immediately in the animal’s
Iberian pigs in southern Europe to produce         oxygen consumption, but the delay is only of
highly prized hams. These hams are consid-         short duration and the so-called oxygen debt
ered to have special flavour due to the tannins     is usually made up in a few minutes by
and fatty acids in the acorns. The tissues of      increased respiration. Changes in oxygen
pigs fed acorns have high concentrations of        consumption of an animal thus provide a
  -tocopherol, which reduces oxidative dam-        good indication of the heat produced by activ-
age to the tissue. The crude protein of acorns     ity. Even mild exercise can cause a consider-
is low (about 60 g kg 1) and their digestible      able increase in oxygen consumption, and
energy for pigs is 11–12 MJ kg 1. Acorns           therefore in heat production, and at higher
contain hydrolysable tannins which degrade to      levels of activity increases of up to ten times
produce pyrogallol. The consumption of             the resting oxygen consumption can be sus-
acorns has been responsible for pyrogallol         tained for prolonged periods, e.g. in draft ani-
toxicity in cattle.                        (TA)    mals, sheep being herded, racehorses and
                                                   animals in flight from predators.
Actin          A water-soluble protein (molecu-        There have been few direct measurements
lar weight 43,000) containing 376 amino            of the metabolic cost of activity in farm ani-
acids. It is found in muscle and other tissues     mals. Most estimates take the form of com-
with motile function. It provides the thin fila-    parisons of heat produced under different
                                             Adaptation                                           7




conditions, such as standing vs. lying, walking     Ad libitum feeding              Feeding at will.
vs. standing still, walking uphill vs. walking on   Unlimited access to feed allows animals to sat-
the level. These comparisons are surprisingly       isfy their appetites at all times. Synonymous
consistent, even between species. When cattle       with full feeding. Their intake when feeding ad
and sheep stand up, the effort involved in get-     libitum is termed voluntary food intake.
ting up causes increased oxygen consumption                                                   (MFF)
of some 30% over a few minutes, after which
the standing:lying ratio is of the order of         Adaptation                 The term adaptation
1.12–1.20:1. The metabolic cost of contin-          implies that there is some sort of norm from
ued standing over lying has been estimated as       which the body or system deviates in response
0.07 to 0.14 watts kg 1 body weight (6–12           to changes in the normal environment. Within
kJ kg 1 day 1). In horses, which have the           the normal population a range of values is
ability to sleep whilst standing, there is little   seen for any particular criterion that is exam-
difference in oxygen consumption between            ined, whether it be, say, activity of an
standing and lying.                                 enzyme, a blood parameter or body weight.
    The cost of movement on treadmills has          Thus there is the statistical concept of the
been measured for animals and humans. The           normal distribution. Adaptation implies a shift
results for horses, cattle and sheep may be         in the normal distribution or in the values for
very crudely summarized as the increase in          a particular individual. The former may be a
heat production per kg body weight in moving        long-term phenomenon in response to, e.g.,
a distance of 1 m; it is 1.5–3 J kg 1 m 1 for       climatic change where those animals best
horizontal movement and 25–35 J kg 1 m 1            suited genetically to the change will survive.
for vertical upward movement. Speed of the          Short-term adaptation implies that the physio-
movement has little effect on these estimates       logical systems can respond to changes in
of total energy cost, because the effort of         external factors. These factors include envi-
rapid movement has to be sustained for less         ronmental temperature, light cycle or
time to cover the same distance. All these          intensity, stocking density, the physical envi-
treadmill measurements may seriously under-         ronment and nutrition (particularly in relation
estimate the practical energy cost to animals       to energy or protein intake). In general, the
of moving over soft or otherwise difficult           term can relate to a modification that lessens
ground. Experiments on animals dragging             the negative impact of imposed change or
loads suggest that the mechanical work per-         takes advantage of an opportunity afforded.
formed (i.e. force        distance) multiplied by       One major aspect relates to changes in
three provides an approximate estimate of the       environmental temperature. Homeothermic
extra heat produced by the animal. The meta-        animals tend to have a defined range of tem-
bolic cost of activities of humans, who are         perature – the thermoneutral zone – within
cooperative subjects, has been extensively          which core body temperature remains con-
studied and may provide a guide as to what          stant without any change in heat production.
may be expected in animals.              (JAMcL)    The thermoneutral zone varies for different
                                                    species and stages of development and may
                                                    also be modified by adaptation of an animal to
Further reading
Blaxter, K.L. (1989) Muscular work. In: Energy      prolonged exposure to an environment that
   Metabolism in Animals and Man. Cambridge         falls outside the thermoneutral zone. How-
   University     Press,    Cambridge,    UK,       ever, within the zone, different species have a
   pp. 147–179.                                     wide range of mechanisms by which they can
                                                    adapt to maintain homeostasis. For example,
Acylglycerol        A form of lipid made up         poultry can increase heat loss in warm envi-
of one glycerol molecule combined with three        ronments by increasing blood flow to the
individual (not necessarily identical) fatty acid   comb, wattles and shanks and, conversely,
molecules attached to the glycerol by ester         can reduce heat loss by reducing blood flow,
bonds. Acylglycerols form part of the neutral       changing posture and piloerection, thus
lipid fraction.                             (NJB)   improving body insulation. Pigs, individually
8                                         Additive, feed




housed, alter posture to increase or decrease      McAllister (1984), who observed a reduction
heat loss and, in groups, can significantly         of approximately 25% in calculated mainte-
reduce heat loss by huddling together. Envi-       nance requirement over a 3-week period.
ronmental temperatures below the ther-             Changes in organ size relative to body weight
moneutral zone result in shivering, which is a     have been observed during undernutrition
rapid noradrenaline-induced mechanism for          of a wide variety of species, including poul-
increasing heat production. Prolonged expo-        try, pigs, cattle and sheep, and can be con-
sure to low temperature results in an increase     sidered as contributing to the improved
in basal metabolic rate, due to non-shivering      economy of the system. Conversely,
thermogenesis. This adaptation takes several       increases in energy intake during lactation
weeks to complete in response to a perma-          are associated with increased digestive organ
nent reduction in environmental temperature.       capacity and increased metabolic rate. Simi-
    Feed intake is increased at low tempera-       larly, offering a high-fibre (less digestible) diet
tures and reduced at temperatures close to         to non-ruminants results in increased diges-
or above the upper limit of the thermoneu-         tive organ size and weight, particularly in the
tral zone. In the case of domestic fowl, food      hindgut, and increased energy supply from
intake declines linearly across the normal         microbial fermentation.
range     of    environmental       temperature        In summary, the human or animal body
(15–30°C). Stocking density and availability       has a wide range of mechanisms for coping
of trough space can also lead to marked            with external stressors and a multitude of
changes in food intake. In pigs, for example,      short-term and long-term adaptations have
it has been observed that intakes are              been reported, of which only a few examples
10–15% higher with individually housed ani-        have been discussed above.              (KJMcC)
mals compared with those in groups. It is          See also: Energy intake; Thermoregulation;
unclear whether this is a behavioural adapta-      Voluntary food intake
tion to boredom on the part of individual
pigs or depression of intake due to competi-
tion in groups. However, there is a wide           Key references
                                                   Koong, L.J. and Nienaber, J.A. (1987) Changes of
range of behavioural adaptations associated          fasting heat production and organ size of pigs
with changes in the physical environment             during prolonged weight maintenance. In: Moe,
etc. For example, stereotypic behaviours             P.W., Tyrell, H.F. and Reynolds, P.J. (eds)
such as bar-biting by sows tethered in stalls        Energy Metabolism of Farm Animals. EAAP
and reductions in tail-biting and aggression         Publication No. 32. Rowman & Littlefield, Lan-
by pigs provided with the opportunity to root        ham, Maryland.
are negative and positive examples of such         McCance, R.A. and Mount, L.E. (1960) Severe
adaptations.                                         undernutrition in growing and adult animals. 5.
                                                     Metabolic rate and body temperature in the pig.
    Of particular importance is the ability of
                                                     British Journal of Nutrition 14, 509–518.
the body systems to respond to changes in          McCracken, K.J. and McAllister, A. (1984) Energy
nutrition, especially in relation to energy and      metabolism and body composition of young pigs
protein. One of the most extreme examples            given low-protein diets. British Journal of
of response to undernutrition relates to stud-       Nutrition 51, 225–234.
ies by McCance and Mount (1960) on young           Mount, L.E. (1979) Adaptation to Thermal Envi-
pigs. These pigs were maintained for long            ronment. Edward Arnold, London.
periods on just sufficient quantities of a nor-
mal diet to maintain body weight. Whereas          Additive, feed           Any substance that is
the maintenance requirement (MR) of nor-           regularly added to feeding stuffs to alter their
mal piglets would be around 550 kJ kg 1            characteristics or nutritive value. Within the
metabolic body weight (W0.75), these under-        European Community the term has been
nourished pigs showed an MR of 250 kJ kg 1         assigned a particular meaning, primarily for
W0.75. The speed with which such changes           clarity in feeding stuffs legislation (The Feed-
occur in response to energy or protein depri-      ing Stuffs Regulations 2000 [SI 2000 No.
vation was demonstrated by McCracken and           2481]) as follows.
                                               Additive, feed                                         9




   A substance or preparation used in animal            in the manipulation of viscosity of liquid feed-
   nutrition to                                         ing stuffs, and those with more specific uses
   (a) affect favourably the characteristics of feed    such as E488, polyoxyethylated glycerides of
       materials, compound feeding stuffs or animal     tallow fatty acids, permitted for calves at no
       products,
                                                        more than 5000 mg kg 1 in milk replacer
   (b) satisfy the nutritional needs of animals or
       improve animal production, in particular by
                                                        feeds only.
       affecting the gastro-intestinal flora or the          Vitamins A, D2 and D3 are permitted for
       digestibility of feeding stuffs,                 the supplementation of a variety of feeding
   (c) introduce into nutrition elements conducive      stuffs but mainly in milk replacer feeds. The
       to obtaining particular objectives or to meet-   simultaneous use of E670, vitamin D2 and
       ing the nutritional needs of animals at a par-   E671, vitamin D3, is frequently prohibited.
       ticular time or,                                 An example of more general use is E671, vit-
   (d) prevent or reduce the harmful effects caused     amin D3, which can be used for cattle up to a
       by animal excretions or improve animal envi-     maximum of 4000 IU kg 1 of a complete
       ronment.
                                                        feeding stuff.
This excludes everything not covered by EU                  Trace elements, in the forms listed, can be
Council Directive 70/524/EE concerning                  added to animal feeding stuffs. Their condi-
additives in feeding stuffs.                            tions of use are subject to close control. For
    Recognized and permitted additives are              example, E4, copper, can be added in various
listed in the pertinent directive by different          forms, including basic cupric carbonate, mono-
groups under their allocated EU reference               hydrate (Cu(CH3.COO)2.H2O) and cupric sul-
numbers and name or description together                phate, pentahydrate (CuSO4.5H2O), to the
with qualifying information where appropri-             diets of fattening pigs up to 16 weeks of age,
ate. The qualifying information includes spe-           provided that the total (added plus background
cific additive name, chemical formula, kind of           level) does not exceed 175 mg Cu kg 1 of the
animal for which it may be used, maximum or             complete feeding stuff. For other species and
minimum quantity permitted and any special              categories of farm animals, the total (added
conditions of use. The various categories of            and background) level of copper in the com-
additives are as follows.                               plete diet must not exceed 35 mg kg 1 but for
    Permitted antioxidants, added to feeding            ovines the permitted upper limit is 15mg Cu
stuffs to help prevent oxidative deterioration.         kg 1 of complete feeding stuff.
For example: E304, 6-palmitoyl-L-ascorbic                   Aromatics and appetizing substances
acid, C22H38O7, permitted for use in any                include natural substances and corresponding
feeding stuff.                                          synthetic products as well as artificial sub-
    Permitted colourants, included in feeding           stances such as E954ii, sodium saccharin,
stuffs to modify the colour of animal products          C7H4NNaO3S, which is permitted for piglets
used as human food, such as eggs (yolk                  up to 4 months of age to a maximum inclusion
colour) or salmon and trout (flesh colour). For          of 150 mg kg 1 of a complete feeding stuff.
example: E161I, citranaxanthin, C33H44O,                    Preservatives are divided into two groups.
permitted in the nutrition of laying hens so            The first includes substances used mainly in
long as the content in a complete feeding stuff         the feeding of farm livestock such as E280,
does not exceed 80 mg kg 1 alone or with                propionic acid, C3H5O2Na. Within this group
other carotenoids and xanthophylls.                     hydrochloric acid (HCl) and E513, sulphuric
    Permitted emulsifiers, thickeners and                acid (H2SO4), can only be used in the prepa-
gelling agents, used to manipulate the viscos-          ration of silage. Most of the preservatives in
ity of liquids or the ‘set’ of feed blocks or           the second group are permitted only in feed-
buckets. This category of additive is more              ing stuffs for dogs and cats or other compan-
often used in the preparation of feeding stuffs         ion animals. For example, E217, sodium
for companion animals rather than farmed                propyl 4-hydroxybenzoate, C10H11O3Na, is
livestock. The category is subdivided into              permitted in any feeding stuff for companion
those permitted for use in any feeding stuff,           animals.     E285,     methylpropionic     acid,
such as E415, xantham gum, most often used              C4H8O2, may be used in feeding stuffs for
10                                           Adenine




ruminants at the beginning of rumination at        1.8      109 CFU for each additional 100 kg
levels between a maximum of 4000 mg kg 1           body weight.
and minimum of 1000 mg kg 1 in complete                Zootechnical additives are substances such
feeding stuffs                                     as antibiotics, coccidiostats, other medicinal
    Acidity regulators are permitted primarily     substances or growth promoters which are
in feeding stuffs for dogs and cats. An exam-      listed in one or more of the groups specified in
ple is E500I, sodium carbonate.                    Part I of Annex C to Council Directive
    Permitted binders, anti-caking agents          70/524/EEC concerning additives in feeding
and coagulants are used to improve the             stuffs. They are listed linked to either a person
physical characteristics of feeding stuffs as in   responsible for their marketing, species or cate-
the production of stable, durable pelleted         gory of animal and other constraints of use.
feeding stuffs or the maintenance of meals in      For example: the antibiotic Avilamycin 200 g
a free-flowing form. For example E565, ligno-       kg 1 (MaxusG200, Maxus 200; Eli Lilly and
sulphonates, can be used as binding agents in      Company Ltd) is permitted for turkeys when
the production of pelleted feeding stuffs.         used between 5 mg and 10 mg active sub-
    Permitted enzymes form a relatively large      stance kg 1. Others are known by their generic
category including substances used to improve      names, such as Antibiotic E714, monensin
the digestibility of feeding stuffs or the effi-    sodium, and Coccidiostat E750, amprolium.
ciency of the animal’s digestive process to            All additives permitted for use in animal
make better use of feeding stuffs or reduce the    feeding stuffs within the EU are continually
level of undesirable excretions. For example:      under review, and from time to time regula-
EC 3.2.1.1, -amylase, produced by Bacillus         tions controlling their use may be changed or
amyloliquefaciens (CBS 360.94) with mini-          modified and entries added or removed.
mum levels of activity of 45,000 RAU g 1 in                                                    (CRL)
solid preparations and 20,000 RAU ml 1 in
liquid preparations can be used for fattening
                                                   Further reading
pigs up to 1800 RAU kg 1 of complete feed-
                                                   European Community (1970) Council Directive
ing stuff, provided that the directions for use       70/524 EEC (JO No L270, 14.12.70, p.1
of the additive or premixture indicate the stor-      OJ/SE Vol. 18, p.4) concerning additives in
age temperature, storage life and stability to        feeding stuffs.
pelleting. A dose rate of 1800 RAU kg 1            Williams, D.R. (2000) Feed Legislation, 4th edn.
complete feeding stuff is recommended and it          HGM Publications, Bakewell, UK, 192 pp.
is used exclusively in compound feeding stuffs
destined for liquid feeding systems containing     Adenine        6-Aminopurine C5H5N5, one
starch-rich feed materials (e.g. < 35% wheat).     of the two purine (adenine, guanine) nucleic
    Selected microorganisms can be added to        acid bases found in DNA and RNA. It is also
feeding stuffs to assist or enhance digestion or   part of molecules that are essential cofactors
digestive efficiency, particularly in feeding       in metabolism, including ATP (adenosine
stuffs for ruminants in which organisms such       triphosphate), ADP (adenosine diphosphate),
as yeast (Saccharomyces cerevisiae) may ben-       NAD (nicotinamide adenine dinucleotide),
eficially modify rumen fermentation. For            NADP (nicotinamide adenine dinucleotide
example: Saccharomyces cerevisiae, CNCM            phosphate), FAD (flavine adenine dinucleotide)
1-1077, in a preparation containing a mini-        and CoA (coenzyme A).
mum of 2        106 colony-forming units (CFU)
                                                                        N
g 1, is permitted in feeding stuffs for dairy
cows at concentrations between 5.5          108
and 1.5 10      9 CFU kg 1 of complete feeding                                     N
                                                                  N
stuff provided that the directions for use indi-
cate storage temperature, storage life and sta-
bility to pelleting. The quantity of S.                                            N
                                                                        N
cerevisiae in a daily ration must not exceed
8.4     109 CFU for 100 kg body weight and                                                    (NJB)
                                             Adipose tissue                                             11




Adenosine diphosphate              (ADP):      see    it protects certain internal organs against phys-
Adenosinetriphosphate                                 ical damage and provides thermal insulation.
                                                          The main WAT depots are subcutaneous,
Adenosine monophosphate (AMP): see                    perinephric (perirenal), pericardial, abdominal
Adenosinetriphosphate                                 (mesenteric and omental, sometimes also
                                                      called gut and channel fat), intermuscular and
Adenosine triphosphate (ATP)                 A        intramuscular. In newborn animals there is
water-soluble compound critical to cellular           very little WAT. It is a late-developing tissue
metabolism. It can store chemical energy for a        that accumulates as animals approach their
short time (seconds to minutes) and then              mature body size.
release that energy to support cellular                   The main cell type found in adipose tissue
processes (ATP → ADP + work + heat). The              is the adipocyte. Adipocytes range in size
energy is derived from the electrons removed          from 20–200 m. The size and number of
during the cellular catabolism of carbohydrate,       adipocytes vary between adipose tissue
fatty acids and amino acids. These electrons          depots. Intermuscular adipose tissue contains
are used to reduce oxygen to water in the             a large number of small adipocytes whereas
mitochondrial electron transport chain. In this       perinephric adipose tissue contains a small
process energy is stored in the terminal phos-        number of large adipocytes.
phate bond when adenosine diphosphate                     The main metabolic processes in adipose
(ADP) is reconverted to ATP.             (NJB)        tissue are: (i) fatty acid synthesis and (ii) triacyl-
                                                      glycerol synthesis, jointly known as lipogene-
Adenylate      cyclase      A cytoplasmic             sis; and (iii) lipolysis, the breakdown of
enzyme involved in the production of the sec-         triacylglycerols to yield glycerol and non-ester-
ond messenger cyclic AMP (cAMP) from ATP.             ified fatty acids (NEFA). Adipose tissue is the
The cellular concentration of cAMP is                 major site of de novo fatty acid synthesis in
increased or decreased by the action of hor-          ruminant species. In non-ruminant mammals,
mones on adenylate cyclase activity. Cellular         fatty acid synthesis occurs in both adipose tis-
responses are modified by changes in the con-          sue and liver; whereas in avian species, adi-
centration of cAMP.                    (NJB)          pose tissue is not an important site of fatty
                                                      acid synthesis and triacylglycerols are synthe-
Adhesion receptors             Receptors (which       sized from fatty acids of dietary origin or syn-
may have other functions) by which bacteria           thesized in the liver. In ruminant adipose
adhere to epithelial cells in the gastrointestinal    tissue, acetate is the primary substrate for
tract. Adhesion is mediated by a specific lectin       fatty acid synthesis. In non-ruminant mam-
on either the receptor or the bacterium.     (SB)     mals and birds, glucose is the major substrate.
See also: Chemical probiosis; Gastrointestinal            Brown adipose tissue (BAT) is a specialized
microflora; Probiotics                                 form of adipose tissue. Its function is the gen-
                                                      eration of heat by the oxidation of fatty acids
Adipocyte            A fat cell, a specialized cell   by the process of non-shivering thermogene-
in particular regions of the body in which neu-       sis. It is particularly important in neonatal ani-
tral fats (triacylglycerols) are stored. Adipocyte    mals. In some species (e.g. lambs) the ability to
diameter can vary over threefold depending            generate heat by non-shivering thermogenesis
on lipid content, which varies between the            is lost within 2–3 days of birth; in others (e.g.
adipose tissue sites in the body.            (NJB)    rats) this property persists into adult life. Some
                                                      species, such as the pig, do not have BAT and
Adipose tissue         There are two types of         are particularly susceptible to cold immediately
adipose tissue: white and brown. White adi-           after birth. BAT is pale brown in appearance,
pose tissue (WAT) is the main site of fat depo-       due to the well-developed blood supply and to
sition in the animal body. Its main function is       the presence of numerous mitochondria in
as an energy store, which accumulates in times        adipocytes. It is found in a number of anatomi-
of positive energy balance and is mobilized in        cal locations, e.g. in interscapular, axillary and
times of negative energy balance. In addition,        perinephric regions. Its ability to generate heat
12                                           Adrenal




is due to the ‘uncoupling’ from ATP synthesis      Aflatoxins              A family of bisfur-
of mitochondrial electron transport by uncou-      anocoumarin metabolites of toxigenic strains
pling proteins (UCPs). These proteins cause        of Aspergillus flavus and A. parasiticus.
the disruption of the proton gradient across           The name derives from Aspergillus (a-),
the inner mitochondrial membrane.       (JRS)      flavus (-fla-) and toxin. The major aflatoxins
                                                   (AFs) are AFB1, B2, G1 and G2. The AFs are
Adrenal         The adrenal gland is located       bioactivated by hepatic enzymes to toxic
above the anterior portion of the kidney. It is    metabolites including AFB1-8,9-epoxide, and
made up of two distinct anatomical and func-       AFM1 (in milk). The AFs occur in the field in
tional parts, the cortex and medulla. The cor-     seeds (maize, cottonseed, groundnuts) and in
tex secretes three types of hormones:              storage of grains (maize, soybeans).
glucocorticoids, mineralocorticoids and andro-         Biological effects are liver damage (acute
gens. The medulla produces and releases the        and chronic) and liver cancer (chronic),
catecholamine hormones, dopamine, nor-             reduced growth, impaired lipid absorption,
epinephrine and epinephrine.             (NJB)     with induced deficiencies of vitamins A, D and
                                                   K, causing impaired blood coagulation, haem-
Adrenaline: see Epinephrine                        orrhage and bruises (poultry), and adverse
                                                   reproductive effects. Differences in susceptibil-
Adverse effects of food constituents               ity between species of animals relate to the
Any of the major food constituents (protein,
                                                   activity of hepatic cytochrome P450 enzymes,
carbohydrate, fat, mineral, vitamin, fibre,
                                                   which bioactivate AF to the toxic metabolites.
water) can induce adverse effects if they are
                                                   Rabbits, ducks and turkeys are highly suscepti-
not balanced for the requirements of the con-
                                                   ble to AF toxicity, while rats and sheep are
sumer. If the constituents are not balanced,
                                                   less sensitive. Chronic AF intoxication is
the food may be avoided or, if it is the sole
                                                   caused by 0.25 ppm (dietary) in ducks and
food available, intake will be low. One exam-
                                                   turkeys, 1.5 ppm in broilers, 0.4 ppm in
ple is fibre which, being indigestible or only
                                                   swine and 7–10 ppm in cattle. AF metabolites
slowly digested (by microbes in the digestive
                                                   in liver cross-link DNA strands, impairing cell
tract), imposes physical work on the digestive
                                                   division and protein synthesis. AFB1 metabo-
tract as well as limiting the capacity to eat
food. Other examples are specific plant toxins      lites form DNA adducts, causing liver cancer.
that interfere with metabolism, reducing the       AF has immunosuppressive effects, impairing
overall satisfaction the animal derives from       cell-mediated immunity.                    (PC)
each unit of food eaten. Many plants have
evolved these to avoid being eaten. Another        Age at first egg             The age, usually
way in which food can have adverse effects is      expressed in days, at which an individual bird
by the heat produced by its ingestion, diges-      lays its first egg. The mean age at first egg for
tion and metabolism, especially in a hot envi-     a flock of birds approximates to the age at
ronment in which this extra heat is difficult to    which the flock reaches a 50% rate of egg
lose. A diet excessively high in protein can       production (see table).
have such adverse effects due to the heat pro-
duced in the deamination of the excess amino       Typical mean ages at first egg for domesticated birds fed
                                                   ad libitum, with conventional lighting.
acids. Excessive concentrations of individual
minerals, particularly in plants that accumulate   Species                       Mean age at first egg
the minerals as a means of protection, can
induce specific toxicity symptoms or adverse        Domestic fowl                 19–21 weeks
effects by disturbing the mineral balance.         Duck                          16–18 weeks
                                                   Turkeya                       32–34 weeks
Plants with a high water content, such as
                                                   Quail                         6–7 weeks
young herbage, may adversely effect the
intake of dry matter, particularly if require-     aWhen photostimulated at about 30 weeks and following
ments are high and intake capacity is limited.     at least 8 weeks of exposure to short days.
                                           (JMF)                                                    (PDL)
                                              Algae                                              13




Age at weaning                The age, often       Alcohols        Alcohols have a functional
expressed in days, at which a young mammal         ·COH group. The group includes primary,
ceases to receive its mother’s milk. It is also    secondary and tertiary alcohols, with one, two
used, as in calf rearing, to denote the age at     and three ·COH groups. Long-chain alcohols
which any natural or artificial milk is with-       (up to 30 carbons) are found as esters with
drawn from the ration.                 (PJHB)      palmitic acid. Glycerol and cholesterol are
                                                   alcohols. Ethanol, CH3·CH2OH, is an alcohol
Agglutinins: see Haemagglutinins                   produced by fermentation and can be used as
                                                   a source of metabolic energy. It has a caloric
Alanine                           An amino acid    value of 29.7 kJ g 1 or 23.4 kJ ml 1.
(CH3·CH·NH2·COOH,           molecular     weight                                            (NJB)
89.1) found in protein. It can be synthesized
in the body from pyruvate and an amino
                                                   Aldehydes        Aldehydes have a functional
donor such as glutamic acid. Substantial quan-
                                                   ·CHO group. Many six-carbon (e.g. glucose),
tities of alanine are synthesized in gut mucosa
                                                   five-carbon (e.g. ribose) or four-carbon sugars
and muscle, and the alanine not used for pro-
                                                   (e.g. erythrose) have a functional aldehydic
tein synthesis is transported to the liver where
                                                   carbon. Aldehydes are intermediates when a
the enzyme alanine aminotransferase converts
                                                   functional alcohol carbon is converted to an
alanine to pyruvate. Mitochondrial pyruvate in
                                                   acid carbon. Aldehydes such as formaldehyde
the liver can either be used in the TCA cycle,
                                                   and acetaldehyde are highly toxic and react
or it can be converted (carboxylated) to
                                                   with tissues.                            (NJB)
oxaloacetate, some of which is subsequently
reduced to malate, some transaminated to
aspartate, and some decarboxylated to phos-        Aldosterone         A 21-carbon steroid hor-
phoenolpyruvate. All three of these com-           mone synthesized in the adrenal cortex and
pounds can escape the mitochondrion and            classified as a mineralocorticoid. It plays a role
enter the cytosol to be used for gluconeogen-      in sodium retention and potassium excretion
esis. Integration of these processes involving     by the kidney.                             (NJB)
muscle and liver tissue is often referred to as
the glucose–alanine cycle.                         Aleurone         The single outer layer of liv-
                                                   ing cells surrounding the endosperm of cereal
            O                 N                    grains. Rich in protein, these cells synthesize
                                                   the enzyme -amylase, which is responsible
                                                   for the breakdown of the stored starch in the
                                                   endosperm into maltose and glucose during
                                                   germination. The aleurone layer remains
            O                                      attached to the bran during milling.      (ED)
                                                   See also: Cereal grains
                                         (DHB)
See also: Gluconeogenesis; Pyruvate                Alfalfa: see Lucerne

Albumin         Albumins were originally           Algae        Plant-like organisms that possess
classified as proteins that were soluble in a       chlorophyll a in combination with other
50% saturated solution of ammonium sul-            chlorophylls or accessory photosynthetic pig-
phate. Albumins (five separable proteins)           ments, and have minimal differentiation into
account for approximately half of the protein      defined tissues or organs. They range from
in blood plasma. Plasma albumin plays an           single microscopic cells to among the tallest
important role in regulation of osmotic pres-      organisms known (giant kelps, c. 40 m) and
sure. Bilirubin, free long-chain fatty acids       are mainly aquatic, with some tolerating peri-
and a number of steroid hormones are found         odic or prolonged exposure to air.        (CB)
bound to albumin.                      (NJB)       See also: Marine plants; Seaweed
14                                        Algal toxins




Further reading                                   mechanism of action is often not well under-
Hoek, C. van den, Mann, D.G. and Jahns, H.M.      stood, although the toxic effects are typically
  (1995) Algae: an Introduction to Phycology      mediated through the gills. In contrast, the
  (1997 reprint). Cambridge University Press,     toxins associated with human illnesses by con-
  Cambridge, 627 pp.
                                                  sumption of contaminated finfish (e.g. ciguat-
                                                  era fish poisoning, clupeotoxicity) and
Algal toxins          Toxins of algal origin
                                                  paralytic, amnesic, neurotoxic and diarrhoeic
(also called phycotoxins) are most often pro-
                                                  shellfish poisoning (PSP, ASP, NSP and DSP,
duced by unicellular marine flagellates, partic-
                                                  respectively) caused by ingestion of shellfish
ularly dinoflagellates, but also by members of
                                                  are much better known. The phycotoxins
other major flagellate algal groups, such as
                                                  responsible for these syndromes constitute a
raphidophytes, haptophytes and pelago-
                                                  heterogeneous group of compounds, affecting
phytes. A few species of the diatom genus
                                                  a variety of receptors and metabolic
Pseudo-nitzschia synthesize a potent neuro-
                                                  processes, acting as Na+-channel blockers,
toxin, domoic acid. In fresh and brackish
                                                  Ca2+-channel activators, glutamate agonists,
waters, cyanobacteria (‘blue-green algae’) are
                                                  phosphatase inhibitors etc. These pharmaco-
often implicated as toxic algal contaminants
                                                  logically active compounds also include the
in drinking-water supplies for humans and
                                                  emerging problems associated with ‘fast-act-
livestock. In the marine environment,
                                                  ing toxins’ of poorly defined human health
cyanobacterial toxins are responsible for ‘net-
                                                  significance, such as gymnodimine and
pen liver disease’ in caged salmonids. When
                                                  spirolides. Many of the phycotoxins can be
present in high abundance or during periods
                                                  propagated within marine food webs from
of rapid growth (‘blooms’), algae can cause
                                                  phytoplankton through zooplankton (cope-
water discolorations known as ‘red tides’,
                                                  pods, krill), then from ichthyoplankton to
usually in fresh or coastal waters – these phe-
                                                  large carnivorous fish, and even marine birds
nomena are not always associated with toxic-
                                                  and mammals. Toxin accumulation within fish
ity. Toxic events associated with algae may
                                                  stocks (e.g. anchovies) harvested for fish-meal
be divided into two types: (i) those caused by
                                                  production may even be a risk for aquaculture
the production of specific toxic metabolites;
                                                  of certain species. Except in bivalve shellfish,
and (ii) those resulting from secondary
                                                  where oxidative and reductive transformations
effects, such as post-bloom hypoxia, ammo-
                                                  mediated by both enzymatic and non-enzy-
nia release, or other artefacts of decomposi-
                                                  matic processes have been determined, and in
tion on marine flora and fauna. Phycotoxins
                                                  the case of biotransformation within fish tis-
and their causative organisms are globally dis-
                                                  sues of ciguatoxin precursors from dinoflagel-
tributed in marine coastal environments, from
                                                  lates, metabolism of phycotoxins is poorly
the tropics to polar latitudes, and few areas
                                                  understood.                               (AC)
are exempt from their effects, which may be
                                                  See also: Marine environment; Marine toxins
expanding in geographical extent, severity
and frequency on a global basis. In a few
cases, this may be linked to eutrophication,      Reference and further reading
but there is no general hypothesis to explain     Anderson, D.M., Cembella, A.D. and Hallegraeff,
all such events.                                     G.M. (eds) (1998) Physiological Ecology of
    Among the thousands of extant species of         Harmful Algal Blooms. NATO Advanced Study
marine microalgae, only several dozen pro-           Institute Series, Vol. 41. Springer-Verlag, Hei-
duce highly potent biotoxins that profoundly         delberg, Germany, 662 pp.
                                                  Botana, L.M. (ed.) (2000) Seafood and Freshwater
affect the health of marine ecosystems, as
                                                     Toxins: Pharmacology, Physiology, Detection.
well as human and other animal consumers of
                                                     Marcel Dekker, New York, 798 pp.
seafood products. As an operational category,     Hallegraeff, G.M., Anderson, D.M. and Cembella,
certain toxic microalgae are often called ‘fish-      A.D. (eds) (2002) Manual on Harmful Marine
killers’ because of their potent direct effects      Microalgae. Monographs on Oceanographic
on fish, particularly in aquaculture systems.         Methodology, Vol. 11. Intergovernmental
Such toxins are poorly characterized and the         Oceanographic Commission, UNESCO, Paris.
                                                 Alkali treatment                                                 15




Acute toxicity (LD50) of selected phycotoxins after intraperitoneal injection into mice. Only major toxin analogues
found in shellfish or finfish, and/or the corresponding toxigenic microalgae, for which the pathology in mammals is
known or highly suspected are included. Note that multiple derivatives of varying toxicity are common for most toxin
groups. Data summarized from citations in Hallegraeff et al. (2002).

Toxin group                   Analogue                      Toxicity ( g kg 1)                  Primary pathology

Azaspiracid                   AZA                                  200                          Gastrointestinal
                              AZA2                                 110                          Gastrointestinal
                              AZA3                                 140                          Gastrointestinal
                              AZA4                                 470                          Gastrointestinal
                              AZA5                               1000                           Gastrointestinal
Brevetoxin                    BTX-B1                                50                          Neurological
                              BTX-B2                               300                          Neurological
                              BTX-B3                             > 300                          Neurological
Ciguatoxin                    CTX1                                   0.25                       Neurological
                              CTX2                                   2.3                        Neurological
                              CTX3                                   0.9                        Neurological
Gambiertoxin                  GTX-4B                                 4.0                        Neurological
Maitotoxin                    MTX1                                   0.05                       Neurological
                              MTX1                                   0.05                       Neurological
                              MTX2                                   0.08                       Neurological
                              MTX3                                   0.1                        Neurological
Okadaic acid                  OA                                   200                          Gastrointestinal;
                                                                                                tumour promotion
Dinophysistoxin               DTX1                                 160                          Gastrointestinal
                              DTX3                                 500                          Gastrointestinal
Gymnodimine                                                         96                          Neurological(?)
Pectenotoxin                  PTX1                                 250                          Hepatotoxic
                              PTX2                                 230                          Hepatotoxic;
                                                                                                gastrointestinal
Saxitoxin                     STX                                   11                          Neurological
                              NeoSTX                                12                          Neurological
Gonyautoxin                   GTX1                                  11                          Neurological
                              GTX2                                  32                          Neurological
                              GTX3                                  16                          Neurological
                              GTX4                                  13                          Neurological
Spirolide                     B                                    200                          Neurological (?)
                              des-methyl-C                          40                          Neurological (?)
Yessotoxin                    YTX                                  100                          Cardiotoxic




Alimentary tract: see Gastrointestinal tract                Alkali treatment            The principle behind
                                                            the treatment of cellulosic substrates with
Alkali disease          A chronic form of                   alkali is that it hydrolyses ester bonds between
selenosis, which occurs in cattle and horses                the cell wall polysaccharides (cellulose and
after prolonged consumption of plants with                  hemicellulose) and lignin, rendering the mater-
high selenium concentrations. It is charac-                 ial more susceptible to rumen microbial degra-
terized by alopecia, hoof dystrophy, lack of                dation. Early techniques in the late 19th
vitality, emaciation, poor quality hair,                    century were industrial processes requiring
sloughing of the hooves and stiff joints.                   both heat and pressure. However, in the
Although not widespread, it is of major                     Beckmann process, the first on-farm method-
importance in some localized areas, such as                 ology, cereal straw was soaked for up to 2
parts of the Great Plains of North America.                 days in a dilute (1.5%) sodium hydroxide solu-
                                     (CJCP)                 tion, then washed to remove any excess
16                                        Alkali treatment




alkali. This technique improved degradability       additional benefit is that sodium hydroxide
but considerable soluble (i.e. potentially          treatment has a preservative effect on high-
degradable) material was lost during the wash-      moisture grain, reducing both bacterial and
ing process. The use of more concentrated           fungal growth. Offered to cattle, treated grain
solutions, either sprayed on to chopped or          maintains a higher rumen pH, tends to
shredded straw, or applied by dipping baled         increase the acetic:propionic acid ratio, and
straw into vats which was then allowed to           reduces the incidence of rumenitis in compari-
‘mature’ for up to a week prior to feeding,         son with cattle fed conventionally processed
reduced these losses. The delay ensured that        material. Similarly, when high levels are
residual sodium hydroxide had reacted with          offered to dairy cows, depressions in milk fat
carbon dioxide, to form sodium carbonate.           content are minimized and roughage intake is
Because alkali treatment raises the ash con-        maintained.
tent, the apparent digestibility of organic mat-        The requirement for supplemental dietary
ter improves less than that of dry matter.          nitrogen, and the observation that other alka-
    The response to treatment varies inversely      lis also improved digestibility, led to the devel-
with the quality of the untreated straw. To         opment of systems using either gaseous (NH3)
realize the potential improvement in degrad-        or aqueous (NH4OH) ammonia. Ammonia is
ability, sufficient dietary nitrogen and sulphur     injected into straw stacks sealed with plastic
must also be provided. Sodium hydroxide is          sheeting or film, or into large bales, as either
the most commonly applied alkali, though            gas (straw must contain at least 10% moisture)
potassium hydroxide (often as wood ash), cal-       or solution (100 l of 300 g NH3 l 1). Under
cium hydroxide, alkali hydrogen peroxide and        temperate summer temperatures the process
calcium oxide (lime) have all been used. A dis-     is generally complete in 4–6 weeks and
advantage of the technique is that water con-       results in organic matter digestibility increas-
sumption is increased (a potential drawback in      ing from 45% to 55% and intake by anything
arid regions), leading to increased urine out-      up to 30%. Nitrogen content is also enhanced
put, which generates a problem with quantity        (1.4 vs. 0.8% in dry matter), thereby increas-
and disposal of bedding. The high urinary out-      ing rumen microbial activity and yield. It is
put of sodium may damage soil structure.            recommended that, as nitrogen retention is
    The technique has also been used to treat       directly proportional to the straw moisture
cereal grain. The action disrupts the integrity     content, treatment should occur as soon as
of the seed coat, increasing the accessibility of   possible after combining. Treatment with gas
the starch to the rumen microorganisms with-        can also be undertaken in ‘ovens’. Oven treat-
out the requirement for physical processing.        ment takes only 24 h and enables straw to be
Conventionally harvested grain is blended           treated during periods of cold weather or
with sodium hydroxide, water is then added          under winter conditions. An added advantage
and the material mixed. This reaction pro-          is that ammonia treatment inhibits spoilage
duces considerable heat, following which the        organisms, especially moulds, thereby increas-
grain should be remixed prior to storage. The       ing the storage properties of damp straw.
amount of sodium hydroxide required for opti-           In tropical environments the high ambient
mum digestibility varies with the fibre content      temperatures mean that the treatment of rice,
of the grain husk. About 25 kg t 1 is used          maize or sorghum straws is achieved in 2–3
with wheat and 40–45 kg t 1 for oats.               weeks. Urea, or even urine, can be used as
Treated grain can be fed direct or after mixing     the ammonia source, as the higher tempera-
with water, which causes the seed coat to           tures speed the conversion of urea to ammo-
swell and rupture. The slower release of            nia by urease enzymes present in straw.
starch relative to that from ground or rolled       Urease levels have been enhanced by the
grain interferes less with fibre degradation,        addition of jackbeans to the straw prior to
allowing higher intakes of roughage to be           treatment.
maintained. Residual alkali helps to maintain           Toxic symptoms may arise if high quality
rumen pH, reducing the incidence of acidosis        forages (e.g. grass or lucerne hay) are ammo-
when high levels of grain are offered. An           niated and offered to ruminants. This takes
                                              Allantoin                                                       17




the form of a hyper-excitability, commonly           Alkalosis         A pathological condition in
referred to as ‘crazy cow syndrome’, which is        which the arterial plasma pH rises above 7.4.
totally unconnected with bovine spongiform           The range of alkalosis that is compatible with
encephalopathy (BSE). Roughages with a high          life is 7.4–7.7. An example is metabolic alka-
carbohydrate content prior to ammoniation            losis resulting from excessive loss of gastric
are particularly implicated, with the com-           acid during prolonged vomiting. This also
pound generally associated with this effect, 4-      involves considerable loss of potassium in the
methylimidazole, being formed by the                 urine. Treatment is by intravenous infusion of
interaction of sugars with ammonia in the            isotonic saline containing supplementary
rumen.                                   (FLM)       potassium chloride to correct both the chlo-
                                                     ride and potassium deficits. The bicarbonate
Alkaline phosphatase              An enzyme          excess corrects itself.                 (ADC)
found in intestinal contents that catalyses the
release of phosphate from a wide variety of
phosphorylated cellular metabolites and co-          All-trans retinoic acid            A metabolic
factors (e.g. sugar phosphates, nucleotides,         derivative of vitamin A (all-trans retinol) or β-
ATP). It is also found in tissues such as liver,     carotene via the intermediate formation of all-
bone, and kidney which are sources of plasma         trans retinol. Retinoic acid interacts with
alkaline phosphatase. In bone it is thought to       nuclear retinoic acid receptors (there are four)
contribute to crystal formation.          (NJB)      to affect appropriate genes, which result in
                                                     cellular differentiation.                  (NJB)
Alkaloids          A class of plant secondary
compounds generally characterized as con-            Allantoin        C4H6N4O3, a degradation
taining at least one basic heterocyclic nitrogen     product of purines. It is an intermediate in the
atom and usually possessing some type of             production of uric acid that can be converted
physiological activity. They are found in            in part to urea except in birds and reptiles.
approximately 15% of all vascular plants.
Alkaloids are a heterogeneous group of com-                         O
                                                                                              N
pounds, subdivided and further classified by a
                                                                                 N
similar basic chemical structure containing the
nitrogen atom. Alkaloids comprise several                                                              O
thousand different structures and possess a                             N
                                                                                          N
wide variety of physiological activities and
potency. Some of the key sources of plant
material containing alkaloids affecting animal                               O
nutrition are listed in the table.        (DRG)                                                            (NJB)



Alkaloids.

Alkaloid class                  Plant or organism                           Physiological effect

Diterpene                       Delphinium                                  Neurotoxic
Indole                          Claviceps, Peganum, Phalaris                Neurotoxic, vascular
Indolizidine                    Swainsona, Astragalus, Physalia             Glycosidase inhibitor, teratogenic
Piperidine                      Conium, Lupinus, Nicotiana                  Neurotoxic, teratogenic
Pyridine                        Nicotiana                                   Neurotoxic
Pyrrolizidine                   Senecio, Crotalaria, Heliotropium           Hepatotoxic, pneumotoxic,
                                                                            photosensitization
Quinolizidine                   Lupinus, Thermposis, Cytisus, Baptisia      Teratogenic, myotoxic, neurotoxic
Steroidal                       Solanum, Veratrum, Zigadenus                Teratogenic, cholinesterase inhibitor
Tropane                         Datura, Atropa, Hyoscyamus                  Neurotoxic, blindness
18                                          Allowance




Allowance        Nutrient requirements rep-        cursors of active hormones (e.g. histidine to
resent the best estimates for the particular       histamine, 5 hydroxy-tryptophan to serotonin
species, age and production system based on        etc.).                                  (NJB)
the available scientific evidence. The term
‘allowance’ takes account of the need to           Amino acid            Amino acids contain the
include a safety factor on top of ‘require-        elements C, H, N, O and S. Their basic struc-
ments’ to allow for variations in environmen-      ture in solution is (R·CHNH3+·COO–) which is
tal conditions and individual variability in       referred to as a ‘zwitterion’ because the alpha
requirements. Allowances are usually set at        carbon (·CHNH3+) has a positively charged
5–10% above requirements.             (KJMcC)      nitrogen attached and the carboxyl group
                                                   (·COO–) is negatively charged. The amino
Aluminium          The most abundant metal         acid R group (side chain) can be aliphatic,
in the earth’s crust. Its low solubility ensures   contain hydroxyl (-OH) groups, have sulphur,
that the concentration in most plant and ani-      have basic groups which contain nitrogen or
mal tissues remains low. The only evidence of      have various aromatic rings. Amino acids are
toxicity in farm animals comes from its inter-     the basic units of which protein is constructed
action with essential nutrients, in particular     and amino acids can be modified to provide a
phosphorus and magnesium in ruminants and          wide variety of products that are required for
iron in poultry, possibly leading to deficiencies   an animal to function.
in those elements in range livestock. Neuro-
behavioural disorders have been demonstrated                                O
at high aluminium intakes in laboratory ani-                      R
mals, by those seeking to determine the role
of aluminium in the development of                                              O–
Alzheimer’s disease in humans.           (CJCP)                       N
                                                                                            (NJB)
Amadori products           Intermediates in        See also: individual amino acids
the reaction of phenylhydrazine with mono-
saccharides (e.g. glucose) to form glucose         Amino acid metabolism                Although
phenylosazones. Amadori products are unde-         there are hundreds of naturally occurring
fined intermediates in Amadori rearrangement        amino acids, only 20 are normally found as
in the production of, for example, glucose         components of protein. Other amino acids
phenylosazone from glucose phenylhydra-            not found in protein are products (e.g. tau-
zone.                                  (NJB)       rine) or intermediates (e.g. ornithine or cit-
                                                   rulline) in essential metabolic processes.
Amide        A compound with the specific           Amino acids have the general formula,
carbon–nitrogen linkage R·CON·R. The pep-          R·CHNH2·COOH. In solution they are ‘zwit-
tide bond between amino acids in proteins          terions’, meaning that the ·COO– is negatively
is an amide linkage. Familiar amides are           charged and the ·NH3+ is positively charged.
the amino acids asparagine and glutamine           The metabolism of amino acids involves their
in which an amine nitrogen (·NH2) is linked        incorporation into a wide variety of proteins,
to a carboxyl-carbon, e.g. asparagine,             their release from protein during protein
NH2CO·CH2·CH(NH2)·COOH.               (NJB)        turnover and their use in the production of
                                                   essential peptides (e.g. glutathione) and as
Amine        A compound with the specific           precursors of other amino acids and essential
carbon–nitrogen linkage R·CNH2. The sim-           metabolites. In the body approximately 1% of
plest amine is methylamine (CH3·NH2) in            all amino acids are found as free amino acids
which one of the hydrogens of ammonia has          while 99% are bound in protein, with a small
been replaced by a methyl (CH3·) group. Free       fraction found as polymers such as peptides
amino acids can be considered as amines.           and hormones.
Some amines produced by decarboxylation of             For animals, the main source of amino
amino acids or modified amino acids are pre-        acids is the diet, though in some animals
                                      Amino acid metabolism                                       19




(especially ruminants) amino acids are pro-        are precursors of ketone bodies or give rise to
duced by gut microflora during fermentative         them directly (acetoacetate) and are called
digestion and then become available for the        ketogenic amino acids (leucine, lysine and
animal’s use. Amino acids are absorbed from        tryptophan). Some amino acids give rise to
the small intestine as free amino acids or as      both types of intermediates and are both
di- and tripeptides and released into the blood    glucogenic and ketogenic (isoleucine, phenyl-
mostly as free amino acids but some peptides.      alanine and tyrosine). The main site of catabo-
Cellular uptake of each amino acid is depen-       lism of amino acids is the liver but the
dent on transporter(s) for neutral amino acids     catabolism of the branched-chain amino acids
(both sodium dependent and sodium indepen-         may involve both muscle and liver. The capac-
dent) and for cationic and anionic amino           ity for carrying out transamination with subse-
acids.                                             quent production of the branched-chain
    For non-ruminant animals, amino acids are      ketoacids is higher in muscle while the capac-
classified as dispensable (i.e. can be synthe-      ity to catabolize the branched-chain ketoacids
sized at rates equal to the need), conditionally   via a branched-chain ketoacid dehydrogenase
indispensable (i.e. can be made from the basic     is greater in the liver.
carbon skeleton with nitrogen provided by              Another example of inter-organ coopera-
transamination) or indispensable (which must       tion is seen in the transport of nitrogen from
be supplied fully formed in the diet). The dis-    amino acid catabolism in muscle to the liver
pensable amino acids are alanine, glycine, ser-    via the ‘alanine cycle’. Nitrogen from the
ine, cysteine, aspartic acid, glutamic acid,       branched-chain amino acids and other sources
proline, hydroxyproline and tyrosine. The          is combined with pyruvate to produce alanine,
conditionally indispensable amino acids are        which is transported to the liver: the nitrogen
arginine (for birds, fish and young mammals),       can then be incorporated into aspartic acid
histidine, phenylalanine, tryptophan, leucine,     and then into urea. In urea production one of
isoleucine, valine and methionine. The indis-      the two nitrogens in urea comes from ammo-
pensable amino acids are threonine and             nium and the other from aspartate. The nitro-
lysine, which do not participate in transamina-    gen from amino acid catabolism in mammals
tion reactions. Since animals cannot synthe-       is excreted in urine as urea (CN2H4O) and
size the carbon skeleton of the conditionally      ammonium ion (NH4+). The production of
indispensable amino acids, these are normally      urea is restricted to the liver and involves five
required in the diet in addition to lysine and     enzymes, two of which are in the mitochondr-
threonine. For ruminant animals, the same          ial matrix. This subcellular division in the site
classification applies but a large proportion of    of urea production requires transporters
the amino acids required can be derived from       (ornithine/citrulline, malate, aspartate, gluta-
microbial synthesis in the rumen. Rabbits and      mate) located in the inner membrane of the
laboratory rodents derive a portion of their       mitochondrion and gives rise to the potential
amino acid needs by caecotrophy (see               for transporter control of urea synthesis.
Coprophagy).                                       Other nitrogen-containing compounds found
    Part or all of the carbon skeleton of some     in urine (e.g. creatinine) are not part of a dedi-
amino acids (arginine, alanine, aspartic acid,     cated nitrogen excretion pathway.
cysteine, glutamic acid, histidine, hydroxypro-        In birds, the end-product of nitrogen excre-
line, isoleucine, methionine, phenylalanine,       tion is uric acid (C5H4N4O3). Production of
proline, serine, threonine, tyrosine and valine)   uric acid requires two one-carbon units from
provides carbon for the production of glucose      the folate system and thus competes with
(see Gluconeogenesis). These amino acids           other systems requiring one-carbon units as
are called glucogenic amino acids. Both the        part of their metabolism. Fish excrete nitrogen
liver and kidneys are involved in the produc-      as ammonium or urea depending on whether
tion of glucose from amino acids and from          their environment is fresh or salt water. The
three-carbon intermediates (pyruvate and lac-      excretion of urea by saltwater fish is thought to
tate) from glucose catabolism. Other amino         be related to the higher osmotic pressure of
acids provide intermediates (acetyl-CoA) that      salt water relative to that of the body.
20                                        Amino nitrogen




    A number of amino acids are precursors of      Glucosamine, galactosamine and manno-
such essential products as haem, purine,           samine are examples. Glucosamine is a com-
pyrimidine, hormone and neurotransmitters.         ponent of heparin, while the N-acetyl
Arginine, in concert with methionine and           derivative is found in hyaluronic acid. Galacto-
glycine, gives rise to creatine. Lysine in pro-    samine, as the N-acetyl derivative, is a com-
teins is methylated by S-adenosylmethionine        ponent of chondroitin. Mannosamine, as the
to trimethyllysine which, after the protein is     N-acetyl derivative, is a component of sialic
broken down, becomes part of carnitine. His-       acid.                                     (NJB)
tidine gives rise to histamine. Histidine bound
in certain proteins (e.g. actin and myosin) is     Amino-oligopeptidase: see Aminopeptidase
methylated by S-adenosylmethionine to form
3-methylhistidine which, upon protein degra-       Aminobutyric           acid      Aminobutyric
dation, is released but cannot be re-used for      acid can be found in two forms. -Amino-
protein synthesis. Because it is quantitatively    butyric acid (HOOC·CH2·CHNH2·COOH)
excreted in the rat and human, it has been         is    produced      by    transamination     of
used to estimate muscle protein catabolism.          -ketobutyric acid produced in the catabolism
Histidine, with β-alanine, forms the dipeptide     of threonine and methionine. -Aminobu-
carnosine: β-alanine also combines with 1-         tyrate (H2NCH2·CH2·CH2·COO ) is a neuro-
methylhistidine to form the dipeptide anserine     transmitter formed by the decarboxylation of
and with 3-methylhistidine to form balenine.       glutamate.                               (NJB)
Phenylalanine is a precursor of tyrosine. Tyro-
sine provides the basic structure for DOPA,        Aminopeptidase           A peptidase that
dopamine and norepinephrine. Tryptophan,           cleaves peptide bonds from the N-terminal of
                                                   peptides, e.g. leucine amino peptidase (EC
after conversion to 5-hydroxytryptophan, is
                                                   3.4.11.1), which is attached to epithelial cells
converted into serotonin. Methionine, via its
                                                   of the small intestine.                    (SB)
conversion to S-adenosylmethionine, is a
                                                   See also: Protein digestion
source of methyl carbons for numerous
methylations. Additionally, after conversion to
                                                   Aminotransferases          Enzymes that are
S-adenosylmethionine, methionine provides
                                                   involved in transfer of an -amino nitrogen
sulphur for the biosynthesis of cysteine (the
                                                   from one amino acid to the ketoacid precur-
carbon comes from serine), carbon for the
                                                   sor of another amino acid. Aminotransferases
biosynthesis of spermidine and spermine and
                                                   can be found in many tissues and in the
carbon for purine synthesis via folate-depen-
                                                   cytosolic as well as mitochondrial fractions of
dent one-carbon metabolism.                (NJB)
                                                   cells. The accepted vitamin co-factors for
                                                   transamination reactions are pyridoxine
Amino nitrogen           The amine nitrogen
                                                   5 -phosphate (removal of -NH2) and pyridox-
(-NH2) attached to the -carbon and, in some
                                                   amine 5 -phosphate (addition of -NH2). (NJB)
cases, the terminal carbon of an amino acid.
The reaction of ninhydrin with -amino nitro-
                                                   Ammonia            Ammonia (NH3) is a gas at
gen of free amino acids was an early basis for
                                                   normal ambient temperatures. It is produced
quantifying amino acids.
                                                   industrially and used as a fertilizer for crops by
                          O                        injection into the soil. It is toxic, even fatally,
                 R                                 and is an irritant to membranes exposed to it.
                                                   It reacts with water to become ammonium
                              O–
                                                   hydroxide (NH4OH). In amino acid metabo-
                      N                            lism it can be released as ammonium (NH4+)
                                          (NJB)    from the amino acid glutamine by the enzyme
                                                   glutaminase or from the amino acid glutamate
Amino sugars          Monosaccharides (sim-        by the enzyme glutamate dehydrogenase.
ple sugars) in which a single hydroxyl group       Because ammonium can be incorporated into
(-OH) is replaced by an amino group (-NH2).        glutamate by the enzyme glutamate dehydro-
                                          Anabolic steroids                                       21




genase or into glutamine by glutamine syn-          Amylase          An enzyme ( -amylase; 1,4- -
thetase, ammonium nitrogen (NH4+) in the            D-glucan-glucanohydrolase;       EC     3.2.1.1)
form of ammonium citrate (C6H14N2O7) can            secreted in the saliva of omnivorous animals
be used as a source of nitrogen for the biosyn-     and from the pancreas. The enzyme hydroly-
thesis of dispensable amino acids in non-rumi-      ses starch and glycogen and produces the dis-
nants. In the rumen, bacteria convert urea-N        accharides maltose and isomaltose, and also
into ammonium-N which is then incorporated          maltotriose and -limit dextrins. Preparations
into microbial amino acids and protein, which       of -amylase (EC 3.2.1.2) have been isolated
are later digested and become available to the      from various sources, e.g. bacteria, barley
host in the form of absorbed amino acids.           malt and sweet potato, and are used for struc-
                                          (NJB)     tural investigations of polysaccharides.    (SB)

Ammonia         treatment        The feeding        Amyloglucosidase           An enzyme (EC
value of cereal straw for ruminants is              3.2.1.3) that acts on terminal units of (1→4)-
improved by treatment with ammonium                 linked glucans from the non-reducing end,
hydroxide. Ammonia is applied to straw (bar-        releasing glucose.                        (SB)
ley, oat, wheat) enclosed in a plastic sheet for
4–6 weeks (in temperate summer conditions).         Amylopectin          A branched polymer of
In tropical conditions, treatment of straw (rice,   glucose which has a role as a storage form
maize or sorghum) is achieved in 2–3 weeks.         of carbohydrate. Starch (from plants) and
Ammonia is injected into straw stacks or large      glycogen (from animals) consist of amylose,
bales as gas (straw must contain at least 10%       with linear chains of (1→4) glycosidic bonds,
moisture) or solution (100 l of 300 g NH3 l 1).     together with amylopectin, in which linear
Treatment with gas can also be undertaken in        chains of glucose are interspersed with
‘ovens’. ‘Oven’ treatment takes only 24 h and       branches due to (1→6) glycosidic bonds.
allows straw to be treated in cold winter con-                                              (NJB)
ditions. Treatment increases organic matter
digestibility (by c. 10% units, from c. 45%)        Amylose         A linear polymer of glucose
and intake (by c. 30%) and increases nitrogen       which has a role as a storage form of carbo-
content (from 0.8 to 1.4% of dry matter),           hydrate (energy reserve) found in both plants
thereby increasing the activity and protein         and animals. Found in starch (from plants)
yield of rumen microbes. An added advantage         and glycogen (from animals), amylose con-
of ammonia treatment is inhibition of spoilage      sists of linear chains of glucose units with
organisms, thereby increasing the keeping           α(1→4) glycosidic bonds.               (NJB)
quality of damp straw. Under tropical condi-
tions, urea (or possibly urine) is used as a        Anabolic steroids            Steroid hormones
source of ammonia. Urea is converted to             (often synthetic) that stimulate anabolic
ammonia by the action of the enzyme urease          processes, in particular protein synthesis from
present in straw. Jackbeans can also be used        amino acids, whilst inhibiting catabolism and
as a source of urease.                      (EO)    in this respect act antagonistically to glucocor-
See also: Alkali treatment                          ticoids. These agents promote retention of
                                                    nitrogen, potassium and phosphate. The
                                                    effect is to promote weight gain, providing
Key reference                                       nutritional status is adequate. May act by influ-
Sundstol, F. and Owen, E. (1984) Straw and Other    encing the transfer of amino acids from tRNA
   Fibrous By-products as Feed. Elsevier, Amster-   to ribosomes. Often derived from testosterone
   dam, 604 pp.                                     esters or 17 -methyl dihydro-testosterone
                                                    although oestradiol and its derivatives may
Ammoniated feeds: see Ammonia treat-                also be effective. Typical examples used to
ment                                                promote growth in farm animals, particularly
                                                    in beef cattle, are stilboestrol, trenbolone
Ammonium: see Ammonia                               acetate, boldenone, nor-ethandrolone and
22                                               Anaemia




ethylestrenol. The use of these agents in food-         amino acids. To function nutritionally, ana-
producing animals is banned throughout the              logues must be converted to the amino acid
European Union, and enforcement and moni-               at rates consistent with need. Hydroxy-
toring are achieved by routine testing for              methionine is a synthetic source of methion-
residues and metabolites in meat and in ani-            ine used extensively in the poultry industry. It
mal tissue, faeces and body fluid samples.               supports growth roughly equivalent to that
However, they are still widely used in other            obtained with methionine. Most D-amino
parts of the world.                      (MMit)         acids may be considered analogues of the
See also: Anabolism; Glucocorticoids; Growth;           physiological L-amino acids since all but
Muscle                                                  lysine and threonine can be converted to the
                                                        L-amino acid. The keto acids of all amino
Anaemia            A reduction in the number of         acids except lysine and threonine may be
circulating red blood cells (erythrocytes) or in        considered analogues since when used singly
the haemoglobin content of circulating red              they can support growth approaching that
blood cells. Symptoms include pale mucous               with the amino acid.                     (NJB)
membranes, increased heart and respiratory
rate, poor growth rates and exercise intoler-           Analytical methods: see Chromatography;
ance. It is potentially fatal. Causes include:          Gas–liquid chromatography; Mass spectrome-
● Chronic or acute haemorrhage, either                  try; Near infrared spectroscopy; Neutron acti-
    external or internal, due to trauma, vascu-         vation analysis; Nuclear magnetic resonance;
    lar damage, endo- or ectoparasites, War-            Proximate analysis of foods; Weende analysis;
    farin poisoning, platelet deficiency (e.g. in        also individual constituents
    thrombocytopaenic pupura in piglets) etc.
● Excess erythrocyte destruction (haemolytic            Anchovy           A small, schooling, pelagic
    anaemia), initiated for example by infec-           fish found mainly inshore in bays and estuar-
    tions such as babesiosis (red-water),               ies, but not in the open ocean. More than
    Clostridium        oedematiens         (bacillary   130 species of anchovies are distributed in
    haemoglobinurea), or copper poisoning.              many parts of the world. They are important
● Insufficient synthesis of either haemoglobin           human food and animal feedstuffs (fish meal
    or red blood cells, caused by dietary deficien-      and oil) and also used as fertilizers. Anchovies
    cies, e.g. iron in piglets, copper, vitamin B12     swim through the water with their large
    or cobalt, or by conditions affecting bone          mouths open and strain out small organisms
    marrow, e.g. chronic bracken poisoning,             (plankton) with fine, sieve-like structures called
    radiation, certain drugs, leucoses.                 gill rakers.                               (SPL)
● Poisoning, or dietary excesses, e.g. molyb-
    denum, excess feeding of kale and other             Angora goats             Angora goats are
    brassicas, chronic lead poisoning.                  named after the Turkish province, now
    Vaccination is available against some of the        known as Ankara, in which they originated.
infectious diseases that cause anaemia. Treat-          Like other breeds of domesticated goat
ment may be specifically for the primary                 (Capra hircus) they are thought to be
cause or symptomatic therapy. For acute                 descended from the bezoar or wild goat
anaemia, blood transfusion may be appropri-             (Capra aegagrus). The distribution of Angora
ate. Correction or supplementation of the diet          goats was, for many centuries, restricted to
is essential.                                  (EM)     Turkey. In the mid 19th century they spread,
See also: Blood; Haemoglobin; Iron defi-                 firstly, to South Africa and shortly afterwards
ciency anaemia                                          to the USA. Today they are found principally
                                                        in the Middle East, southern Africa and
Anaerobic digestion: see Fermentation;                  Texas, with smaller numbers in other US
Rumen digestion                                         states and in Argentina. In recent decades
                                                        Angora goat populations have been estab-
Analogues, of amino acids          Carbon               lished in a number of European states and in
skeletons that are immediate precursors of              Australasia.
                                               Anions                                              23




    Mature female Angora goats (does) weigh         housed during winter or in the wet season.
about 40–45 kg and males (bucks) around             Their main nutritional requirements are met
60–65 kg. They are farmed for their fibre,           outdoors from grazing and indoors from con-
mohair (not to be confused with angora fibre,        served forage. Some supplementary concen-
which comes from rabbits). Unlike all other         trates are generally supplied during late
goat breeds, which have coats comprising a          pregnancy and in early lactation.    (AJFR)
mixture of coarse and fine fibres, Angora
goats are single-coated: the mohair fleece is        Animal fat         The lipid isolated from animal
composed of only one fibre type and con-             fat depots, mainly triacylglycerols. Fat rendered
tains, or ideally should contain, no coarse         commercially from beef and sheep carcasses is
hairs. In practice most mohair fleeces contain       commonly called tallow. Beef tallow is hard and
a small proportion of coarse hairy fibres            typically contains, as a percentage of total fatty
known as kemps. These have a different mor-         acids, 26% palmitic, 17% stearic, 43% oleic
phology from the true mohair fibres and are          and 4% linoleic acids. Pig fat, called lard, is
regarded as a fault, because they cause prob-       softer due to its greater content of unsaturated
lems in the manufacture of mohair garments          fatty acids. It typically contains 26% palmitic,
and fabrics. Most Angora goats are white but        14% stearic, 43% oleic and 10% linoleic acids.
some breeders specialize in the production of       Since the occurrence of BSE in Britain, tallow
black or brown mohair. The typical mohair           from ruminant species has not been used in ani-
fleece is white, long and lustrous with wavy         mal feedstuffs but has been replaced by alterna-
locks or staples. Mohair grows rapidly, at a        tive vegetable fats with similar physical
rate of 2–2.5 cm per month, and the animals         properties (e.g. palm oil).                 (JRS)
are generally shorn every 6 months to provide
a fibre that meets the requirements of the           Animal production level (APL)             The
processors and to prevent excessive soiling         amount of metabolizable energy (ME) required
caused by the fleece trailing on the ground.         to support the productive state of the animal,
    The average annual mohair production of         relative to its requirement for maintenance.
adult does is between 4 and 6 kg of greasy          For ruminants, APL = (total ME require-
fibre. The yield (i.e. the weight of the clean       ment)/(ME for maintenance).             (JMW)
fleece, after scouring, as a percentage of the       See also: Plane of nutrition
greasy weight) is typically around 75%, though
this varies between different strains within the    Animal protein            Protein from animal
breed. Mohair fibre diameter increases with          sources. The term includes products derived
age, from less than 25 microns ( m) at the          from milk, eggs, meat and fish. As dietary
first shearing at 6 months of age to 35 m or         protein these products are distinguished from
more at about 4 years old. It is now known          plant protein by a generally better quality, in
that both fleece weight and fibre quality (fine-       terms of both digestibility and biological value.
ness) are influenced by nutrition. High levels of    In general, animal protein sources have higher
feeding, particularly of high-protein diets, lead   concentrations of essential amino acids, espe-
to the production of heavier fleeces with            cially lysine and the sulphur amino acids, than
coarser fibres, i.e. there is an inverse relation-   most plant protein sources.                (MFF)
ship between quantity and quality.
    Like other domesticated breeds, Angora          Anions        Anions can be inorganic or
goats are seasonally polyoestrus. Does come         organic. They carry a negative charge. The
into heat at 21-day intervals during the breed-     major anions in blood plasma are bicarbonate
ing season which, in the northern hemisphere,       (HCO3–), chloride (Cl–), phosphate (PO42–),
extends from about August to February. Gesta-       sulphate (SO42–) and organic acids (R·COO–).
tion length averages about 150 days.                To maintain anion/cation balance, the anions
    The principal mohair-producing countries        are balanced by an equivalent charge in the
have dry climates and in these conditions the       form of cations (positive ions) such as potas-
goats can be kept outdoors throughout the           sium (K+) and sodium (Na+).             (NJB)
year. In other countries Angora goats are           See also: Acid–base equilibrium
24                                           Anoestrus




Anoestrus          A period of infertility, ovar-   Key reference
ian inactivity or sexual quiescence which may       Shinneck, F.L. and Harper, A.E. (1977) Effects of
be seasonal (in sheep, goats, horses etc.) or          branched-chain amino acid antagonism in the
induced by nutritional imbalances, stresses            rat on tissue amino acid and keto acid concen-
                                                       trations. Journal of Nutrition 107, 887–895.
(such as heat, cold, confinement, poor man-
agement etc.), disease, lactation or old age.
                                                    Antagonist           A compound that blocks
Nutritional causes of anoestrus include inade-
                                                    the physiological action of another com-
quate intake of energy, micronutrient imbal-
                                                    pound. For example, acetylcholine released
ances and toxicoses. Xenobiotics that
                                                    by parasympathetic nerves binds intestinal
contribute to infertility include oestrogen-like    muscarinic receptors to stimulate motility.
compounds, phyto-oestrogens from some               Atropine also binds these receptors but does
clovers, zearalenone from Fusarium moulds,          not increase motility. Thus atropine can act as
ergot alkaloids, locoweeds (swainsonine), Leu-      an antagonist by outcompeting acetylcholine
caena (mimosine), mustard family (glucosino-        for these receptors, effectively blocking acetyl-
lates) and selenium deficiencies or toxicoses.       choline actions.                           (JPG)
                                           (KEP)
                                                    Anthocyanins            These plant pigments
Anorexia         Lack of appetite, markedly         are glycosides containing a nucleus (aglycone)
low voluntary food intake or complete absti-        called an anthocyanidin. Anthocyanidins are
nence from food. There are numerous causes,         flavonoids, or water-soluble phenolic deriva-
including infectious or non-infectious disease,     tives. They are generally red, crimson, blue,
unavailability of acceptable, nutritious feed       purple or yellow. They tend to be metaboli-
and certain mental disorders. Seasonal inap-        cally inert in animals but some have antioxi-
petence seen in winter in many species should       dant activity. They form dimers (procyanidin)
not be regarded as anorexia. True anorexia is       which can polymerize to form condensed tan-
rare in non-human animals as there is natural       nins (proanthocyanidins).                 (PC)
selection against it.                     (JMF)
                                                    Antibiotic         Antimicrobial pharmaceuti-
Antagonism           A negative interaction         cal, usually of plant or fungal origin. Although
between a nutrient and other nutrients or           the primary use of antibiotics is in the treat-
between nutrients and non-nutrients. The            ment of infections, certain antibiotics are used
interaction may be related to uptake or to          as feed additives in order to improve growth
use. An example is branched-chain amino             and feed conversion. The modes of action of
acid antagonism in which three- to fourfold         antibiotics used as growth promoters probably
increases in dietary leucine in a low-protein       include reduction in sub-clinical disease, thin-
diet result in decreases in food intake and         ning of the wall of the intestine and, in rumi-
weight gain and in the blood and tissue con-        nants, a change in the microflora and fauna in
centrations of the other branched-chain             the rumen. In the late 1990s, some antibiotics
amino acids, valine and isoleucine, and their       previously licensed in the European Union for
keto acids. Another amino acid example is           use as growth promoters (zinc bacitracin, vir-
the lysine–arginine antagonism in which             giniamycin, avoparcin) were banned because
two- to threefold increases in dietary lysine       of fears that their use might encourage the
result in an increase in the need for argi-         development of antibiotic resistance and prej-
nine. Antagonisms can be found in mineral           udice the treatment of human disease. All
interactions in which one mineral affects the       antibiotics must be used with care and the cur-
rate and extent of uptake of another mineral        rent data sheet should be consulted for
such that more of the other mineral is              dosage, contraindications and other precau-
required in the diet. Examples are zinc–            tions: many may be used by Category A man-
copper, zinc–iron, calcium–zinc, calcium–iron,      ufacturers only. Some may be incorporated
calcium–phosphorus, iron–copper and many            into feed blocks or used as top-dressing of
more.                                   (NJB)       feeds such as silage.
                                       Antimicrobial activity                                     25




    Flavophospholipol is licensed for use in        Immunoglobulin). Antigens that stimulate
pigs, domestic fowls, turkeys, rabbits, calves,     the production of antibodies can be from the
growing and fattening cattle and fur animals.       environment, food, infection or vaccination.
It is a phosphoglycolipid, and is not absorbed         Plasma cells in the mammary gland pro-
from the digestive tract, so is not metabolized     duce antibodies (IgA) shortly before parturi-
by the animal. It changes the pattern of            tion, that are concentrated in the colostrum
rumen microorganisms by inhibiting some             and are also present in declining amounts in
Gram-positive bacteria and by reducing the          early lactation. Circulating antibodies (IgG) are
formation of peptidoglycan.                         also transported and concentrated in the
    Monensin is licensed for use in non-lactat-     colostrum. They provide the potential source
ing cattle. It has had fatal effects when fed to    of passive immunity to most of the domestic
horses, and when fed to cattle within 7 days        species. The relative importance of IgG and
before or after being treated with tiamulin.        IgA varies with species. The greater the num-
Monensin is an ionophore, and is poorly             ber of antigens the dam has been exposed to,
absorbed from the digestive tract, about two-       the more antibodies there are likely to be in
thirds being lost unaltered in faeces.              the colostrum, assuming adequate health and
Ionophores facilitate the movement of ions          nutrition.                                  (EM)
across membranes by forming hydrophobic             See also: Antigen; Colostrum; Immunity
complexes with ions such as potassium and
sodium, and in so doing disrupt bacterial cell      Antigen         Any substance that stimulates
walls, and possibly the cell walls of protozoa.     an immune response. Many different sub-
They thereby change the pattern of rumen            stances can act as antigens, but most are pro-
microorganisms, reducing the production of          teins of more than 20 amino acids.
acetate, butyrate and methane, and increasing       Microorganisms act as antigens but their com-
the proportion of propionate. Since methane         plex structure provides many antigenic sites or
is a waste product, the efficiency of rumen          epitopes. Large protein molecules may also
activity is improved. Ionophores also reduce        have many epitopes.                       (EM)
the total mass of bacteria and thereby decrease     See also: Antibodies; Immunity
the amount of dietary protein degraded.
    Avilomycin is licensed for use in pigs,         Anti-infective        agents     Anti-infective
broiler chickens and turkeys. Salinomycin is        agents in feedstuffs include natural phyto-
an ionophore available for use in pigs and          chemicals and feed additives (e.g. antibiotics).
also used to prevent coccidiosis in broiler         Phytochemicals with anti-infective activity,
chickens.                                (WRW)      especially against protozoa, include phenolic
See also: Additive, feed; Growth promoters          compounds and saponins. They cause lysis of
                                                    protozoal cell membranes. Anti-infective phy-
Antibodies         Long-chain globulin pro-         tochemicals in herbal products may become
teins produced by plasma cells in response to       more important if use of antibiotics as feed
the presence of an antigen (foreign protein) as     additives is restricted.                  (PC)
part of the body’s defence system. Antibodies
are made of two light and two heavy peptide         Antimicrobial activity           The ability to
chains. Constant regions are common to all          kill or impair the growth of bacteria or proto-
antibodies; variable regions are specific to the     zoa. Many natural toxins have antimicrobial
antigen that stimulated their production, and       action and most antimicrobial pharmaceuti-
can form a site that binds with that specific        cals used today are of plant or fungal origin.
antigen to form an antigen–antibody com-            Although many antimicrobials are used to
plex. This aids the elimination or destruction      treat infections, others impair the digestion of
of that antigen.                                    feed, especially in ruminants. Plants such as
    Antibodies are produced in five different        broom snakeweed (Gutierrezia spp.), pine
classes, depending on the structure of the con-     needles and sage brush (Artemesia spp.) con-
stant regions, and this determines the site in      tain toxins that inhibit rumen fermentation
the body at which they have their action (see       and reduce animal production.              (BLS)
26                                      Antinutritional factors




Antinutritional factors           Antinutritional         Phytates are divalent mineral ions com-
factors (ANFs) are feed components that have         plexed with organic phosphorus in seeds.
negative effects on the intake or utilization of     Phytate phosphorus is poorly available to
feeds, or that may be inherently toxic when          non-ruminant livestock. Most (50–70%) of the
ingested. Many common feeds, such as                 phosphorus in cereal grains is in the form of
legume seeds, contain ANFs; many rangeland           phytic acid. Phytates may be soluble (e.g.
plants contain phytochemicals or toxins. The         sodium or potassium) or insoluble (e.g. cal-
most important ANFs are alkaloids, haemag-           cium). Phytates readily complex with phytic
glutinins (lectins), phenolics, phytates, phyto-     acid and inositol in cereal grains, and these
oestrogens, saponins, tannins and trypsin            chelates then bind much of the phosphorus
inhibitors.                                          and zinc in grains, while complexing to a
    Alkaloids are cyclic organic compounds           lesser extent with copper, cobalt, magnesium
containing nitrogen. When ingested they may          and calcium. Phosphorus deficiency is charac-
cause feed refusal, abortion, birth defects,         terized by distorted appetite, reduced weight
wasting diseases, agalactia, and death. There        gains and impaired reproduction. Zinc defi-
are marked animal species differences in reac-       ciency is manifested by reduced weight gains
tions to alkaloids, which may be due to differ-      and skin lesions. Through microbial fermenta-
ences in rumen microbial metabolism or in            tion in the rumen, ruminants are capable of
the absorption, metabolism or excretion of           cleaving phosphorus from phytates, making it
alkaloids or may be directly related to alkaloid     available to the animal. Phytates are particu-
affinity to target tissues such as binding at         larly high in maize and in wheat by-products,
receptor sites. Alkaloids constitute the largest     and are also present in most other cereal
class of plant secondary compounds, occur-           grains. Adding the industrial enzyme phytase
ring in 20–30% of perennial herbaceous               to pig and poultry rations may be economi-
species in North America. Major categories of        cally feasible, because phosphorus is relatively
toxic alkaloids include pyrrolizidine (e.g.          expensive to supplement; it also reduces
Senecio), quinolizidine (e.g. Lupinus), indoliz-     phosphorus elimination in faeces.
idine (e.g. Astragalus), diterpenoid (e.g. Del-           Phyto-oestrogens are plant oestrogens that
phinium), piperidine (e.g. Conium), pyridine         affect reproduction. Phyto-oestrogens inhibit
(e.g. Nicotiana) and steroidal (Veratrum-type)       release of reproductive hormones and com-
alkaloids. Management schemes to prevent             pete with oestrogen at cellular receptors.
losses are usually based on recognizing the          Hence, livestock consuming forages contain-
particular toxic plant, knowing the mechanism        ing phyto-oestrogens exhibit reductions in fer-
of toxicity, and understanding the temporal          tility, including abnormal oestrous cycles and
dynamics of plant alkaloid concentration and         ovulation, and defective development of
consumption by livestock. Once these are             reproductive organs and genitalia. Forages
understood, losses may be reduced by main-           that typically contain phyto-oestrogens include
taining optimal forage conditions, adjusting         lucerne and clover (Trifolium spp.). Cattle are
grazing pressure and the timing of grazing,          much less sensitive to phyto-oestrogens than
strategic supplementation, changing livestock        are sheep, which appear to activate phyto-
species and herbicidal control.                      oestrogens in the rumen to more potent com-
    Phenolic compounds are produced by a             pounds and may also have more sensitive
wide range of plants. Low molecular-weight           oestrogen receptors. Poultry may also be
(MW) plant phenolics are often converted to          affected by phyto-oestrogens; there is some
tannins when plants mature. When ingested,           evidence that quail are adversely affected by
phenolics reduce feed intake and weight gain.        phyto-oestrogens in range plants.
After ingestion, phenolics are absorbed, pro-             Saponins are steroidal or triterpenoid gly-
ducing negative effects on physiological func-       cosides that have considerable biological activ-
tions. Conversely, hydrolysable tannins may          ity. Saponins have a bitter taste, reducing the
be converted to low MW phenolics in the              palatability of feeds. They may also reduce the
gastrointestinal tract of ruminants and may be       digestion and absorption of nutrients, including
toxic (see Tannins).                                 minerals. These effects occur primarily in non-
                                           Antioxidant                                          27




ruminant livestock. Nevertheless, saponins in     buckwheat, barley and maize. There are two
some range plants from the Caryophyllaceae        classes of trypsin inhibitors: the low-MW
(pink) family (e.g. Drymaria, Agrostemma,         Bowman-Birk inhibitor and the larger Kunitz
Saponaria) or in snakeweed (Gutierrezia spp.)     inhibitor. The anti-tryptic activity is destroyed
can have toxic effects in ruminants, including    by moderate heat, which may be applied dur-
loss of appetite, weight loss, diarrhoea, abor-   ing the processing of plant materials. The
tion and photosensitization. The primary live-    Bowman-Birk inhibitors are more heat-stable
stock feed with significant amounts of             than the Kunitz type. Excessive heating may
saponins is lucerne (Medicago sativa), which      reduce protein quality through non-enzymatic
causes frothy bloat. The concentration of         browning reactions. Ruminant livestock are
saponins in lucerne changes seasonally, with      less affected than non-ruminants, because
the highest amounts in midsummer.                 most trypsin inhibitors are degraded slowly in
    Tannins are high-MW phenolic com-             the rumen though some may escape the
pounds that bind strongly with proteins and       rumen and enter the small intestine. In poul-
other macromolecules such as starch, cellu-       try, trypsin inhibitors cause pancreatic
lose or minerals. Two major classes of tannins    enlargement and reduce feed efficiency and
are hydrolysable and proanthocyanidins (con-      growth rates; in pigs and calves, growth rates
densed tannins). Tannins reduce feed intake       are depressed from reduced protein digestibil-
because of astringency (i.e. reduced accept-      ity without accompanying pancreatic enlarge-
ability) and reduce digestibility by the forma-   ment. Trypsin inhibitors from soybeans may
tion of largely indigestible complexes in the     be added to bovine colostrum, resulting in
digestive tract. Deleterious effects vary         increased immunoglobulin absorption in
depending on the type of tannin and the toler-    calves.                                     (JAP)
ance of the animal, but concentrations above      See also: Alkaloids; Haemagglutinins; Lectins
10–20% may be toxic to ruminants. Clinically
affected ruminants may show signs of kidney       Antioxidant         Antioxidants     can     be
failure and elevated serum urea nitrogen.         organic or inorganic and nutrient or non-
Non-ruminant animals may have reduced             nutrient in nature. They function to protect
growth rates with low (i.e. < 5%) concentra-      animal tissue against highly reactive oxygen-
tions; higher concentrations may be fatal.        containing products produced chemically and
Tannins are common in plants, occurring in        by metabolism. These so-called reactive oxy-
both gymnosperms and angiosperms. Woody           gen species (ROS) can be organic or inor-
species and broadleaf plants are more likely to   ganic compounds in which oxygen is a critical
contain tannins than are Gramineae. Com-          component. Their production is linked to the
pounds such as polyethylene glycol (PEG) may      use of oxygen as the primary electron accep-
be added to feed and water to bind and inacti-    tor in aerobic metabolism. Compounds such
vate tannins, allowing high-tannin feeds to be    as superoxide anion (·O2–), hydrogen peroxide
used for grazing or pen-fed livestock. For        (H2O2), hydroxyl radical (·OH), alkoxyl radical
ruminants, tannins may have some positive         (RO·) and peroxyl radical (ROO·) attack cellu-
effects through complexing with high quality      lar lipid, protein, DNA and carbohydrate.
protein (allowing it to bypass rumen degrada-     Chemical attacks on the unsaturated fatty
tion) or through increased nitrogen recycling     acids of cellular membranes produce products
to the rumen.                                     such as the peroxyl radical (ROO·), which ini-
    Trypsin inhibitors are plant proteins that    tiates a chain reaction that can lead to com-
inhibit the pancreatic enzyme trypsin, which is   promised cell membranes and eventually cell
partly responsible for protein digestion.         death.
Trypsin (and other protease) inhibitors bind          The antioxidants available to the cell are
tightly to trypsin and chymotrypsin, inhibiting   vitamin E, vitamin A, carotenoids, vitamin C
their proteolytic activity. Trypsin inhibitors    and glutathione. Vitamin E is a fat-soluble vit-
occur primarily in legume seeds, particularly     amin involved in inhibiting chain reactions ini-
soybeans, but are also found in low concen-       tiated when peroxyl radicals react with
trations in cereal grains such as wheat, oats,    long-chain unsaturated fatty acids that contain
28                                      Antiparasitic agents




three or more double bonds. An identifiable          ROOH. Here 2GSH react with HOOH to
product of this attack is malondialdehyde,          produce 2H2O and GSSG. When HOOH is
which can be measured by assays dependent           not catabolized by glutathione peroxidase it
on thiobarbituric acid (TBA). TBA products          can, in the presence of ferrous iron (Fe2+),
have been used as indicators of oxidative           produce the hydroxyl radical ·OH, which is
damage to membrane lipids. The chain reac-          the most reactive oxygen metabolite and
tion producing malondialdehyde is terminated        thought to be involved in tissue damage as
when a peroxyl radical (ROO·) reacts with -         indicated by production of malondialdehyde
tocopherol to produce an -tocopherol radical        from unsaturated fatty acids and O-tyrosine
intermediate that reacts with another peroxyl       from protein-bound phenylalanine.     (NJB)
radical to produce a non-radical product such
as -tocopherylquinone. To be effective, tis-
sue     -tocopherol concentration must be           Key reference
above a critical threshold. Below the threshold     Liebler, D.C. (1993) The role of metabolism in the
peroxyl radicals propagate and deplete -               antioxidant function of vitamin E. Critical
tocopherol while above the threshold peroxyl           Reviews in Toxicology 23, 147–169.
radicals are suppressed by the more than ade-
quate     -tocopherol reserve. The average          Antiparasitic agents             Parasites may
tocopherol concentration in membranes is            colonize either the internal or external
one -tocopherol per 500–1000 phospho-               medium of animals, or occasionally both, but
lipid molecules (Liebler, 1993).                    are present in greatest numbers outside their
    Another nutrient antioxidant is vitamin C       host animal vector. Currently treatment of
(ascorbic acid). It is not known whether the        infected animals is usually based on
role of ascorbic acid is solely in the recycling    anthelmintic agents but resistance is increas-
of the -tocopherol radical produced by the          ing, particularly in nematode worms. Atten-
interaction of a lipoperoxyl radical (ROO·) or      tion is turning to prophylactic measures, such
whether it has an additional role.                  as the provision of uninfected pasture, and
    Another nutrient-based antioxidant is           biological control, in particular by treatment
reduced glutathione (GSH), which is made up         of the parasite with fungi in its native pasture
of three amino acids in a peptide linkage, -        environment.                             (CJCP)
glutamyl-cysteinyl-glycine. The SH in the
GSH refers to the cysteine portion of the mol-      Antiprotozoal agents                Protozoa are
ecule, which is involved in oxidation/reduc-        single-celled organisms that are often present
tion reactions. In its role as an antioxidant,      in soil and may be transmitted to farm ani-
GSH is converted to oxidized glutathione            mals when feeding or by insect vectors. Many
(GSSG). The enzyme glutathione reductase is         infect the digestive tract; others penetrate vital
involved in interconversion of GSSG to GSH,         organs. A variety of drugs are available to
i.e. GSSG → 2GSH. The reducing equivalents          treat protozoal diseases but they can be diffi-
required to convert oxidized glutathione to         cult to eradicate. Some antibacterial and anti-
reduced glutathione come from glucose-6-            fungal agents have a limited effectiveness in
phosphate via the production of NADPH + H           treating protozoal infections. Chemoresist-
which is converted to NADP when GSSG is             ance is also emerging and new drugs must be
reduced to 2GSH. GSH is involved in conver-         targeted for effective chemotherapy. (CJCP)
sion of the -tocopherol radical to -toco-
pherol with the production of GSSG from             Apo-enzyme           An enzyme form that
2GSH. This could not be shown in animals            requires a co-factor in order to function. The
fed diets deficient in vitamin E. The direct use     intact enzyme protein without the enzyme co-
of glutathione in protection against oxygen-        factor bound to it is called the apo-enzyme.
based damage is the selenium-containing             When the enzyme co-factor is bound to the
enzyme glutathione peroxidase. This enzyme          enzyme protein this combination is called the
is involved in the destruction of hydrogen per-     holo-enzyme. An example is the red blood cell
oxide HOOH (H2O2) and lipoperoxides                 enzyme transketolase. The vitamin co-factor
                                                   Appetite                                            29




thiamine diphosphate binds to the enzyme                     Hunger is often used synonymously with
and aids in the reaction but is not perma-               appetite, but differs in several aspects. Hunger
nently changed by the reaction. This relation-           may be viewed as the ‘stimulus to eat’ that
ship is different from that of other vitamin             arises from internal cues which provide infor-
dependent co-substrates such as NAD or                   mation about energy or essential nutrient sta-
NADP, which are changed to NADH and                      tus. Hunger may be considered the motive to
NADPH, respectively, as a result of the                  eat, in the same way that thirst is considered to
enzyme reaction.                        (NJB)            be the motive to drink. Appetite may arise
                                                         from the same internal cues that are responsi-
Apolipoproteins          Proteins that are               ble for hunger, as well as from the sight or
essential components of the lipid transport              smell of food, or from psychological desires or
system in the body, which involves chylo-                cravings. Appetite often implies a greater selec-
microns and the lipoproteins HDL, LDL, IDL               tivity toward the food(s) consumed than hunger.
and VLDL (high-density, low-density, interme-                In contrast to food intake, which can be
diate-density and very low-density lipopro-              quantified in terms of the amount of food con-
teins). Two general types of lipoproteins are            sumed per unit time, appetite is difficult to
identified: those that are integral (e.g. apo B-          quantify and so the mechanisms controlling
100), which cannot be removed and are criti-             appetite are not differentiated from the mech-
cal to structure and function; and those that            anisms that control food intake. Food intake is
can be exchanged (e.g. apo A, apo C etc.).               controlled, both on a long-term, day-to-day
Apolipoproteins also act as enzyme co-factors            and within-meal basis. On a long-term basis,
and as ligands for lipoprotein receptors on cell         adult animals will adjust their food intake to
surfaces.                                 (NJB)          maintain a relatively stable body weight. On a
                                                         day-to-day basis, animals will eat a relatively
Apparent digestibility            Digestibility deter-   constant amount of energy each day and will
mined simply from the difference between the             correct for daily perturbations in energy
amount of a nutrient consumed (I) and the                intake. Circadian, diurnal or specific daily
amount excreted in the faeces (F), expressed as          feeding patterns also contribute to how and
a proportion of the intake. Thus apparent                when food is consumed within a day – these
digestibility = (I – F)/I. It is also determined at      patterns can vary greatly between species.
the terminal ileum by measuring the loss of the          Within a meal, there are mechanisms that ini-
nutrient in ileal digesta (D); thus apparent             tiate the meal, sustain the meal and terminate
digestibility at the terminal ileum = (I – D)/I.         the meal. Stimuli arising from within the body
Unlike true digestibility or real digestibility,         (internal) as well as from environmental (exter-
apparent digestibility ignores losses of endoge-         nal) stimuli may be involved in initiating a
nous origin.                                     (SB)    meal. Very little is known about the internal
See also: Digestibility                                  stimuli that initiate a meal. None the less,
                                                         these stimuli are probably energy metabolites
Appetite        An instinctive desire for food           in nature, and signal information regarding
or drink, or any other instinctive desire neces-         energy or essential nutrient (e.g. glucose)
sary to maintain life. Regarding feeding,                stores. The internal stimulus responsible for
appetite is an object or objective, such as              initiating the meal probably gives rise to the
obtaining a food or foodstuff. For example,              feeling of appetite or hunger. External stimuli
during a meal, the appetitive phase is the               that may be involved in initiating a meal can
goal-directed behaviour focusing on acquiring            include social eating habits, the sight or smell
food, while the consumatory phase is the act             of food, or other environmental factors. Sig-
of ingestion. During the consumatory phase,              nals from long-term energy stores such as adi-
mechanisms are initiated that help to termi-             pose tissue also influence feeding, as low
nate the meal. The degree of disposition                 levels of insulin or leptin enhance feeding.
towards obtaining food may vary greatly, so                  The appetite for food is controlled by the
that the appetite may be a subtle or over-               central nervous system (CNS), but is also
whelming compulsion.                                     responsive to metabolic, humoral and vagal
30                                              Appetite




signals originating from the periphery. Meta-         the central pattern generator for the rhythmic
bolic modulators include small transient drops        and stereotyped movements of ingestion (e.g.
in blood glucose that precede a meal, as well         mastication, licking, lapping). The caudal
as hepatic glucose and fatty acid metabolism.         brainstem also receives afferent fibres from
Hormonal signals include factors such as              the mouth, stomach and small intestine.
amylin, apolipoprotein AIV, enterostatin,             Higher cortical brain areas are involved in
oestrogen, leptin, glucagon, glucocorticoids,         multiple aspects of food intake, including
insulin and somatostatin. The vagus nerve             making food associations, such as learned
transmits information to the brain regarding          preferences and learned aversions, controlling
gastric or rumen distention and the release of        motor movements necessary for finding or
gastrointestinal peptides during a meal.              catching food, or making appropriate food
    While it is generally thought that animals        choices.
eat to meet their energy demands, there are               Specific appetites arise from the animal’s
numerous circumstances when this is not true.         attempts to maintain an adequate intake or
Highly palatable diets often cause animals to         prevent a deficiency of dietary essential nutri-
overeat and become obese, while extremely             ents such as protein, vitamins and minerals.
unpalatable diets will cause animals to under-        For example, animals maintain a level of pro-
eat. A diet extremely deficient in an essential        tein intake above their requirement when
nutrient will cause anorexia if it is the only diet   allowed to select between different foods –
available. At the same time, animals fed mildly       this is often considered a specific appetite for
protein-deficient diets may overconsume the            protein. Animals deficient in a specific essen-
diet in an attempt to obtain more protein.            tial nutrient will select foodstuffs or diets con-
Appetite is also suppressed during infection          taining the deficient nutrient over foodstuffs
and cancer. Cytokines such as tumour necro-           lacking the needed nutrient – this is also con-
sis factor- , interleukin-1 and interleukin-6         sidered a specific appetite and serves to
appear to be the primary cytokines responsi-          restore homeostasis in deficient animals. All
ble for infection- and cancer-induced                 specific appetites except sodium appetite
anorexia.                                             appear to require post-absorptive feedback
    Neurotransmitters such as norepinephrine,         and learning before an animal will display a
serotonin, dopamine, histamine and GABA               specific appetite for a given food. That is, the
have all been shown to be involved in the con-        animal must first consume and absorb a spe-
trol of feeding. Neuropeptides or peripheral          cific food that contains adequate quantities of
peptides that act at CNS sites to affect food         the needed nutrient. The brain then senses
intake include agouti-related protein, amylin,        some event associated with the repletion of
  -melanocyte-stimulating hormone, bombesin,          the limiting nutrient or the restoration of
cocaine and amphetamine-related transcript            homeostasis. This ‘positive post-absorptive
(CART), corticotropin-releasing factor, entero-       event’ is then associated with some aspect of
statin, galanin, glucagon, glucagon-like pep-         the consumed food (usually taste) and will
tide, insulin, melanin concentrating hormone,         direct the animal toward obtaining and con-
opioids, orexin (hypocretin), neuropeptide Y,         suming this specific food during subsequent
somatostatin, thyrotropin-releasing hormone           meals. In contrast, sodium appetite is innate
and urocortin. Differences in the role and            and does not require post-absorptive feedback
importance of these neurotransmitters and             or learning. Animals deficient in sodium will
neuropeptides vary with species.                      immediately recognize foods containing this
    Numerous brain areas are involved in the          nutrient.
control of appetite. The hypothalamus plays a             Perverted appetites or pica involve the
critical role, particularly the arcuate nucleus,      intake of inedible or non-nutritive material
paraventricular nucleus, lateral hypothalamus,        such as earth, hair, bone, etc. The purpose of
ventromedial hypothalamic nucleus and the             pica is unknown, but under some circum-
dorsomedial nucleus. The caudal brainstem             stances pica may occur during expression of a
also plays an important role in feeding, as it        learned taste aversion or during states of
contains the motor neurones that function as          nutrient deficiency.                          (NJB)
                                             Aquaculture                                           31




Appetite disorders           Appetite disorders      Pomace may be fed directly to livestock,
may be secondary effects of diseases, most of        dried, or sold moist. Some pomace has
which cause a reduction in food intake, or           absorbents (e.g. wood shavings) added to aid
they may be diseases themselves, such as             juice extraction, which increase the fibre con-
anorexia. Many diseases cause a fever, with          tent and reduce the nutrient concentrations.
elevated body temperature. A reduction in            Apple pomace is palatable and suitable for
food intake occurs, which is presumed to             feeding to adult ruminants but it is low in pro-
derive from a direct effect of the elevated tem-     tein (c. 5%) and in minerals. It is also low in
perature on the brain. Diseases involving            dry matter (DM) and has only the moderate
abdominal discomfort, e.g. ovarian cancer,           energy level of ~10 MJ ME kg 1 DM for cat-
also depress intake: the reduction in intake         tle. Moist apple pomace can be stored for up
should alleviate the discomfort, particularly if     to 6 months covered in clamps and its bulk
the food was the source of the problem.              density when moist is < 150 kg m 3 and
Other diseases are metabolic, i.e. in the body       when dried < 350 kg m 3. The pectin and
as distinct from the digestive tract, and again      pentosan contents make it unsuitable for
a reduction in intake is an innate response to       young ruminants, piglets and poultry. Maxi-
metabolic imbalance or discomfort. In a nor-         mum DM inclusion rates as a percentage of
mal animal, this is most likely to be due to the     diet are 20% for dairy and beef cattle, 10%
food but, even if it is not, intake will still be    for lambs and 5% for ewes, sows and finish-
reduced. On the other hand, there are certain        ers.                                      (JKM)
metabolic abnormalities that lead to an
increased intake; for example, insufficient           Aquaculture          The cultivation of aquatic
insulin secretion, as in diabetes, does not          organisms (fish, molluscs, crustaceans, unicel-
allow normal cellular uptake of glucose, with        lular algae, macroalgae and higher plants),
the result that certain cells (liver, hind-brain)    using extensive or intensive methods in order
signal their shortage of energy to the intake-       to increase the production or yield per unit
controlling circuits of the brain. Appetite dis-     area or unit volume to a level above that
orders are not likely to be transmitted              obtained naturally in a particular aquatic envi-
genetically as they cause infertility and prema-     ronment (Mariculture Committee of the Inter-
ture death.                                (JMF)     national Council for the Exploration of the
See also: Anorexia                                   Sea, 1986). The term does not apply to the
                                                     impoundment of aquatic organisms in order
Appetite stimulant             A single com-         to gain access to favourable markets; nor does
pound or group of compounds that flavours a           it include culture of essentially terrestrial
feed to increase the appetite. These include         organisms (e.g. terrestrial plants grown hydro-
yeasts, mixtures of herbal extracts, distillery or   ponically).
brewing by-products and simple sugars.                   Aquaculture includes pond, raceway, cage,
Appetite refers to the desire of an animal or        pen and raft culture. Marine (as opposed to
bird for food or water, but is generally used to     freshwater) aquaculture has been termed ‘mari-
refer to a long-term effect. A number of com-        culture’. Aquaculture encompasses the culture
pounds have been reported to be effective in         of aquatic organisms for stock enhancement,
the diets of young pigs but the literature is        ocean ranching and ornamental purposes. The
somewhat conflicting. Poultry have < 1% of            objectives of aquaculture are to increase pro-
the taste buds found in humans or other farm         duction above levels occurring in natural
animals and these stimulants are ineffective.        ecosystems and to provide a more stable tem-
                                            (SPR)    poral supply of food organisms of consistently
See also: Flavour compounds                          higher food quality under greater human con-
                                                     trol than can be supplied through the natural
Apple          The juice of apples (Malus spp.)      fisheries. These objectives are realized through
is extracted for apple juice or cider, leaving a     selection of species or strains with higher feed
residue of apple pomace that contains the            conversion efficiencies, higher growth rates,
remaining tissue, skins, pips and stalks.            later maturity and greater resistance to disease.
32                                     Aquatic environment




    Commercial aquaculture is an ancient           Further reading
practice, though large-scale farming is rela-      Pillay, T.V.R. (1993) Aquaculture Principles and
tively recent. The earliest known treatise on          Practices. Fishing News Books, Blackwell Scien-
aquaculture is the Classic of Fish Culture in          tific Publications, Oxford, UK.
                                                   Stickney, R.R. (2000) Encyclopedia of Aquacul-
500 BC by Fan Lei, a Chinese politician
                                                       ture. John Wiley & Sons, New York.
turned fish culturist who attributed his accu-
mulation of wealth to pond production of           Aquatic environment              Aquatic envi-
carp. Oyster culture is known to have been         ronments encompass both freshwater (lakes,
practised in Japan and Greece c. 2000 years        rivers, wetlands) and saline (oceans, estuaries,
ago. Seaweed culture is much more recent,          salt lakes and sloughs) conditions. They dis-
the earliest known text being published in         play a wide range of thermal regimes, pH,
1952 in Japan. Fish farming was first carried       salinity and other chemical characters, clarity,
out in Europe by the Etruscans.                    and degree of movement, all of which deter-
    Aquaculture has become the world’s fastest     mine the type of organisms that occupy them.
growing food production sector for over a          A stagnant pond, for example, is a very differ-
decade, with cultivation of 206 different ani-     ent aquatic environment from a fast-flowing
mal and plant species. Total aquaculture pro-      river or exposed ocean coast. Although
duction in 1998 was 39.4 million metric            aquatic habitat is usually judged to be physi-
tonnes (Mt), valued at US$52.5 billion and         cally more stable than the aerial or terrestrial
growing at an average percentage rate of           environment, it is none the less subject to
11% per year since 1984. Finfish have con-          periodic changes. In temperate latitudes, sea-
tributed over half of the total aquaculture pro-   sonal thermal changes may be considerable,
duction by weight (20 Mt), followed by             from freezing to 30°C or more. Water levels
molluscs (9.1 Mt), aquatic plants (8.5 Mt),        rise and fall seasonally, or more frequently in
crustaceans (1.5 Mt) and others (0.3 Mt).          the case of tides, periodically exposing some
Inland aquaculture, mostly carp culture, cur-      inhabitants to air. Estuarine habitats may
rently accounts for about two-thirds of the        experience large fluctuations in salinity within
total production (excluding seaweed produc-        hours. The organisms that live in these envi-
tion), but mariculture is growing rapidly.         ronments influence the physical properties to
    In 1998 Asia produced 35.81 Mt, over           some extent, as in trapping or producing sedi-
90% of total global production. The world’s        ment, obscuring clarity of the water, or chang-
top ten aquaculture producing countries in         ing the content of oxygen and other chemical
1998 were China (27.1 Mt), India (2.03 Mt),        constituents.                              (CB)
Japan (1.29 Mt), the Philippines (0.95 Mt),
                                                   Aquatic organisms             Organisms living
Indonesia (0.81 Mt), Korea Republic (0.80
                                                   in fresh, brackish and sea water are generally
Mt), Bangladesh (0.58 Mt), Thailand (0.57
                                                   divided into plankton, nekton, benthos and
Mt), Vietnam (0.54 Mt) and Korea DPRP
                                                   neuston (invertebrates, fish, mammals, etc.).
(0.48 Mt). Other countries include USA
                                                   Most fish and aquatic invertebrates are poikil-
(0.44 Mt), Norway (0.41 Mt), Chile (0.36
                                                   otherms (body temperature conforms to
Mt), Spain (0.31 Mt), France (0.27 Mt) and         external environment) with their metabolic
Italy (0.25 Mt). Major aquatic organisms cur-      rate increasing as the water temperature
rently under culture include several species       increases. Marine invertebrates are osmocon-
of carp, scallop, clam, oyster, mussel, prawn,     formers; marine fish, however, maintain their
marine shrimp, salmon, trout, sea bream,           plasma hypotonic to that of the seawater
sea bass and tilapia. Based on anticipated         medium by drinking, reducing urinary water
human population growth, it has been pre-          loss and excreting salt through the gills. Fresh-
dicted that aquaculture production of food         water fish osmoregulate by pumping out
fish must exceed 50 Mt by 2025, assuming a          water while retaining the salts. External respi-
global per capita fish consumption of 13.5          ratory surfaces (gills) must be kept moist for
kg per year.                               (RHP)   gas exchange.
                                           Arabinoxylans                                            33




    In the marine environment, many small           anoxic conditions after death. The large bio-
free-floating eggs are often released and exter-     masses of such plants, e.g. Eichhornia (water
nally fertilized. The larvae are widely dispersed   hyacinth), have sometimes been used as a
and feed on plankton, thus reducing the need        supplement to silage and other livestock feed.
for a large yolk sac within the egg. High mor-                                                 (CB)
tality rates are associated with these plank-
tonic larvae. In a freshwater environment,
generally eggs are either retained by the par-      Further reading
                                                    Cook, C.D.K., Gut, B.J., Rix, E.M., Schneller, J.
ent or associated with the bottom and contain
                                                       and Seitz, M. (1974) Water Plants of the
a large yolk sac, which produces more highly
                                                       World. Dr W. Junk b.v., The Hague, The
developed larvae or juveniles at hatch.                Netherlands, 561 pp.
    Aquatic animals usually excrete nitrog-         National Research Council (US) Subcommittee on
enous wastes in the form of ammonia, a solu-           Underutilized Resources as Animal Feedstuffs
ble toxic substance requiring large amounts of         (1983) Underutilized Resources as Animal
water for its removal.                       (DN)      Feedstuffs. National Academy Press, Washing-
                                                       ton, DC, 253 pp.
Aquatic plants           Vegetation that is nor-    Riemer, D.N. (1993) Introduction to Freshwater
mally associated in nature with standing water,        Vegetation, revised edn. Krieger Publishing Co.,
either permanently or at least for prolonged           Melbourne, Florida, 218 pp.
periods during the year. The plants may be
wholly submerged, or with photosynthetically        Arabinogalactans          Branched hetero-
active parts entirely or partly submerged. In       polysaccharides with molecular weight
the broad sense of the term ‘plants’, they are      16,000–100,000, having varying proportions
represented by flowering plants, ferns,              of D- or L-arabinose, and D-galactose; arabi-
bryophytes, algae and fungi. As marine plants       nose may be present in the furanose or pyra-
are generally categorized separately, the term      nose ring form, galactose in the pyranose
‘aquatic’ is often applied to only the fresh-       form. The backbone frequently consists of
water species. The distinction between true         galactose residues. Arabinogalactans are usu-
aquatic plants and those that inhabit wet soils     ally water soluble and they may be covalently
is unclear and ultimately relies on whether the     linked with protein. They may contain small
plant requires some degree of submersion or         amounts of rhamnose and uronic acids. They
merely tolerates it. Some intrinsically terres-     are the major hemicelluloses in plants.
trial plants can be relegated to aquatic habitats                                           (JAM)
by poor competitive ability on drier soils, e.g.    See also: Arabinose; Dietary fibre; Galactose;
Taxodium (bald cypress). Herbaceous vascular        Hemicelluloses
plants dominate the aquatics, spanning a
large number of families and ranging in size        Arabinose             A five-carbon sugar,
and habit from minute floating species, e.g.         C5H10O5, molecular weight 150, in L- or D-
Lemna and Wolffia (duckweeds), to tall emer-         form and as a pyranose or furanose ring.
gent forms, e.g. Oryza (rice) and Typha (cat-       Does not occur free in nature. A major com-
tails). Freshwater algae comprise at least          ponent of plant polysaccharides. Absorbed in
15,000 species but are mostly microscopic           the small intestine by passive diffusion.
and inconspicuous. Fungi are small filamen-                                                    (JAM)
tous species.
    Aquatic plants are important in stabilizing     Arabinoxylans          Branched heteropoly-
shorelines and purifying water. Ironically,         saccharides      with     molecular     weight
where water movement is minimal, they often         6000–30,000, having varying proportions of
contribute to the destruction of their aquatic      arabinose (usually in L form and as the fura-
habitat by accruing sediment, towards               nose ring) and xylose (in D form and as the
hydrarch succession to terrestrial conditions.      pyranose ring). Arabinoxylans frequently con-
Aggressively growing macrophytes can be nui-        tain linear chains of xylose residues and may
sances, clogging waterways and producing            include small amounts of uronic acids. They
34                                            Arachidic acid




are water soluble and are the major con-               Arginine                          An amino acid
stituents of plant cell walls, particularly in         (NH 2 ·NH·C·NH·(CH 2 ) 3 ·CH·NH 2 ·COOH,
cereals and grasses.                    (JAM)          molecular weight 174.2) found in protein. It
See also: Arabinose; Carbohydrates; Dietary            can be synthesized from arginosuccinate (via
fibre; Hemicelluloses; Structural polysaccha-           citrulline). The arginine synthesized in the liver
rides; Xylose                                          is used primarily for urea synthesis, with lesser
                                                       quantities used for the synthesis of creatine,
Arachidic acid                    Eicosanoic           polyamines and nitric oxide. Arginine synthe-
acid, a saturated long-chain fatty acid,               sized in the kidney can be used for body pro-
CH3·(CH2)18·COOH, shorthand designation                tein synthesis, but avian and most reptilian
20:0. It is found in groundnut oil, rape oil,          species cannot synthesize arginine in either
butter and lard.                       (NJB)           kidney or liver tissue and this makes arginine
                                                       a dietary essential amino acid for these
Arachidonic acid               5,8,11,14-Eicosate-     species. Young mammals can synthesize suffi-
traenoic        acid,      molecular       structure   cient arginine to achieve growth rates that are
CH3·(CH2)4(CH=CH·CH2)4·(CH2)2·COOH, a                  about 50% of maximal, whereas adult mam-
long-chain unsaturated fatty acid, shorthand           mals do not require arginine in the diet
designation 20:4, found in fish and groundnut           because biosynthesis is sufficient to satisfy
oils. It is an essential fatty acid for the cat fam-   their needs. Feline species, however, do not
ily, but can be produced from linoleic acid in         synthesize arginine efficiently and therefore
many animals. This makes linoleic acid an              require arginine in their diet.
essential fatty acid and without it a deficiency
of arachidonic acid is expected. Arachidonic                         N                  O
acid is found in high concentration in mem-
branes as part of the phospholipid fraction.                     N       N                  O
Metabolically it is a precursor of the                                              N
prostaglandins, thromboxanes and leuko-
trienes.                                       (NJB)
                                                                                                  (DHB)
Arctic char (Salvelinus alpinus (L.))                  See also: Citrulline; Urea cycle
The most northerly adapted of the salmonid
fish, with a circumpolar natural range. There           Arsanilic acid         Formerly used as a feed
are both anadromous and strictly freshwater            additive, as a coccidiostat in broilers and as a
forms. Eggs should be incubated at less than           growth promoter in pigs and broilers, which
8°C, and the optimum temperature range for             makes use of its antibacterial properties. Feed
growth is 10–13°C. Iceland is the major pro-           efficiency is increased but residues of arsenic
ducer of cultured Arctic char. A major prob-           occur in meat and offal.                   (JMF)
lem for culture to date has been highly
variable growth rates.                 (RHP)           Arsenic        A mineral element (As) with an
                                                       atomic mass of 74.92. It is found naturally in
Arginase          A cytoplasmic enzyme that            small amounts in sea water and rocks. Soils
catalyses the catabolism of the amino acid L-          contain from 1 to 40 mg kg 1 but can accu-
arginine to urea and L-ornithine. The enzyme           mulate more where arsenical pesticides and
is found in the liver of ureotelic animals             herbicides are used. Vegetables and grains
(human, dog, cat, rat, pig, etc.) but not in uri-      contain < 0.5 mg kg 1; freshwater fish con-
cotelic animals such as birds, in which nitro-         tain an average of 0.75 mg kg 1 and seawa-
gen is excreted mainly as uric acid. In                ter shellfish may contain much higher
ureotelic animals the highest activity of              concentrations. Arsenic compounds can leach
arginase is found in the liver but it can also be      into ground water and contaminate well
found in other tissues such as the kidney,             water. This has prompted some regulatory
brain, mammary gland and red blood cells.              agencies to suggest a limit of 10 g As l 1
                                            (NJB)      drinking water for human consumption.
                                      Artificial rearing of mammals                                     35




    Arsenic as arsenate or arsenite is readily         present significant hazards to animal health,
absorbed from the intestine and some of the            causing gastroenteritis and a rapid drop in
As is converted to the methylated form in the          blood pressure.                      (CJCP)
liver before being excreted in the urine. There
is no known metabolic function for As and it           Artificial drying          Artificial drying of crops
is generally considered to be a toxic sub-             (‘parching’ over fire) dates back to biblical times.
stance. However, some investigators have               Green crop drying is normally associated with
found evidence, though weak, that As might             artificially drying with hot air. This method
have limited nutritional benefit in certain ani-        allows green crops to be preserved independent
mal species, especially ruminants. The phenyl-         of weather conditions, at high nutritive quality
arsenic compounds are the least toxic and are          with low conservation losses (as low as 3% of
used as feed additives in the diets of pigs and        the dry matter). While dried grass accounted for
poultry as a growth stimulant, whereas the             200,000 t in 1972 in the UK, this process
water-soluble inorganic compounds are the              declined in popularity during the 1980s due to
most toxic, resulting in their use as pesticides.      the high cost of fossil fuels. Almost 300 l of oil
Although the element is also considered a car-         is required to dry 1 t of dried grass from a crop
cinogen its trioxide form has been used to             of 80% moisture content. Composition of leafy
induce remission of acute promyelocytic                dried grass can be dry matter (DM) 90%, crude
leukaemia in humans. Low concentrations of             protein 18.7% DM, metabolizable energy
selenium and As have been shown to induce              10.6 MJ kg 1 DM. Barn drying provides a
hypomethylation of DNA in isolated intestinal          method of blowing cold air through a stack of
cell models. This mechanism is thought to              cured hay bales to ensure that the moisture con-
give selenium its anti-carcinogenic properties.        tent of the dried hay is < 12%. Hay preserva-
Whether As has similar properties is not               tives and drying agents allow for increased
known. Natural antagonists to intestinal               flexibility in haymaking systems. Under certain
absorption and organ accumulation of As are            conditions, they can greatly increase the effi-
other dietary minerals such as selenium.               ciency of nutrient preservation. The most com-
    Although the inorganic forms of As are             mon preservatives are organic acid-based
more toxic than the organic forms, it has              formulations. Drying agents available are usually
been reported that cattle and sheep can toler-         carbonate-based products, which may also con-
ate various inorganic As compounds in dietary          tain fatty acid esters.                         (RJ)
concentrations up to 280 mg kg 1 for 60
days or more without ill effects. Pigs also tol-       Artificial rearing of mammals                 The
erate rather high amounts of dietary arsenic,          process of substituting intensive technology for
but have reduced food intake at concentra-             the normal care and nutrition provided by the
tions > 500 mg kg 1.               (PGR, CJCP)         dam in neonatal life. The most extreme need
See also: Selenium                                     applies when offspring have been removed
                                                       directly from the womb by hysterectomy to
                                                       establish minimal-disease flocks or herds. It
Further reading                                        also has a function for neonates deprived of
Anke, M., Glei, M., Arnhold, W., Drobner, C. and       maternal care by an accident, a breakdown in
   Seifert, M. (1997) Arsenic. In: O’Dell, B.L. and    maternal health or because of failure of the
   Sunde, R.A. (eds) Handbook of Nutritionally
                                                       dam to lactate. The boundary between artificial
   Essential Mineral Elements. Marcel Dekker,
   Inc., New York, pp. 185–230.
                                                       rearing and very early weaning is not exact.
Nielsen, F.H. (1990) Other trace elements. In:         Very early weaning following a very short lac-
   Brown, M.L. (ed.) Present Knowledge in Nutri-       tation may facilitate the breaking of the disease
   tion. International Life Science Institute, Wash-   chain from parent to offspring, particularly if
   ington, DC, pp. 294–307.                            this is accompanied by intensive medication of
                                                       the offspring. Some success is claimed for
Arsenicals          Arsenic-based compounds            reducing the incidence of some pig diseases
used as pesticides in crops and livestock,             such as porcine respiratory and reproductive
especially for tick control. Arsenical pesticides      syndrome and enzootic pneumonias.
36                                          Artificial rumen




    For successful artificial rearing, the com-        Artificial rumen           A vessel in which
plex physiological needs must be met. The             rumen contents can be incubated under condi-
environment must be controlled so that the            tions resembling those of the rumen in vivo. It
nutritional, social and physical environment          may be a closed or open system operating
provided by the dam can be simulated in the           batchwise or a continuous-flow stirred tank
essential aspects. The immune system of the           reactor (CFSTR) or chemostat that will
neonate at birth is naive. Rearing is greatly         achieve a steady state. Such systems allow
facilitated if the neonate can receive passive        study of the products of rumen fermentation,
immunity via colostrum or by an equivalent            the population dynamics of rumen microflora
dose of relevant immunoglobulins extracted            or studies of the degradation kinetics of com-
from blood. At birth the gut is permeable to          ponents of forage and feeds, methanogenesis
proteins and the globulins can be absorbed            etc. The most complex of these continuous
directly into the bloodstream. The benefits            fermenters involve dialysis of the products to
may be sustained well towards adult life. Off-        mimic absorption and gaseous exchange.
spring that are totally deprived of colostrum         Temperature, pH and redox potential may be
need ‘hospital quality’ care. This should             monitored or controlled. The system may be
include protection from air- and food-borne           used to study isolated pure cultures or mixed
pathogens, a stable temperature and isolation         microbial and protozoan ecosystems. Artificial
from other livestock. The process of normal-          rumen systems allow study of the time course
ization of the environment needs to be very           of change of substrates, gases and organisms.
gradual and in step with the development of           They are usually kept anaerobic using hydro-
active immunity.                                      gen and reducing agents. Simple batch sys-
    Nutrition during artificial rearing is critical    tems are more easily managed. The ‘Rusitec’
to its success. The closer the artificial diet is to
                                                      is an artificial rumen system devised by
the composition of the natural milk of the
                                                      Czerkawski (1986).                         (IM)
species, the better the outlook. Growth rates
tend to be more normal if the artificial diet is
offered in a liquid rather than a solid form.         Reference
Liquid feeding requires particularly diligent         Czerkawski, J.W. (1986) An Introduction to
hygiene. In ruminants, liquid diets carry an             Rumen Studies. Pergamon Press, Oxford, UK,
additional benefit because they stimulate the             236 pp.
reflex closure of the oesophageal groove and
allow the food to bypass a non-functioning            Artificial sweeteners:        see   Attractants;
rumen. The reflex is assisted by a husbandry           Flavour compounds
routine that raises the expectation of being
fed. The protein source in the artificial diet is      Ascites (or hydroperitoneum)             A non-
critical. The casein in milk has clotting proper-     inflammatory peritoneal effusion, seen as an
ties in the presence of the stomach enzyme            accumulation of serous fluid in the abdominal
rennin, and this attribute aids digestion. Pro-       cavity. Though ascites can be part of general-
teins other than those of milk are often less         ized vascular oedema (vascular hypertension
suitable partly because they do not clot and          or hypoproteinaemia), more typically it results
are usually less soluble. Those of vegetable          from chronic passive congestion of the portal
origin tend to be difficult to digest, because         venous system of the liver, often as a sequel to
the molecules are larger than those of the            hepatic diseases such as cirrhosis or veno-
milk proteins and they may provoke an                 occlusive disease. Other traumatic, neoplastic
immune reaction. Milk fats are easily digested,       or vascular diseases that obstruct venous or
particularly if emulsified, but in dry diets lipids    lymphatic draining can also cause ascites but
rich in medium-chain fatty acids tend to be           are relatively rare. Ascites must be differenti-
the most readily digested. Lactose not only           ated from other accumulation of fluid in the
supplies energy but is also readily fermented         peritoneal space, including exudates from
in the gut, encouraging the development of a          inflammatory diseases or urine from a dam-
friendly, lactobacillus-based flora.         (VRF)     aged urinary system.
                                                Ash                                                37




    There are nutritional, infectious, immuno-        dibenzo-p-dioxin ‘chick oedema factor’. Poi-
logical and toxic diseases that result in liver       soned birds developed extensive hepatic
disease and ultimately cirrhosis. As cirrhosis is     necrosis and cholangiolar hyperplasia and
a non-specific change, definitively identifying         portal hypertension. Heart failure is common
the inciting cause is often a diagnostic chal-        in ascites produced in birds poisoned with
lenge. Toxins that are commonly associated            high-salt diets or furazolidone. Ducklings and
with liver disease in livestock include copper        turkeys appear to be most susceptible to fura-
(sheep are most susceptible), gossypol, pitch         zolidone toxicosis.                      (BLS)
(clay pigeons), cocklebur, lantana, sacahuista,
lechugilla, some vetches, blue-green algae,           Ascorbic acid         L-Ascorbic acid is vitamin
aflatoxins and pyrrolizidine-containing plants         C, C6H8O6. It is required in the diet of pri-
(Senecio, Crotolaria, Amsinkia, Cynoglos-             mates, guinea pigs and some bats and birds. In
sum, Echium, Symphytum and Helio-                     humans a dietary deficiency results in the clas-
tropium spp.). One of the common lesions of           sical symptoms of scurvy in which wound heal-
pyrrolizidine alkaloid intoxication is fibrosis        ing     is   impaired     and     subcutaneous
and obliteration of the heptic central vein           haemorrhages are seen as well as muscle
(veno-occlusive disease).                             weakness, swollen gums and loose teeth. L-
    Avian ascites or broiler pulmonary hyper-         Ascorbic acid is a major water-soluble antioxi-
tension syndrome is a disease of rapidly grow-        dant involved in oxidation/reduction reactions
ing broilers. Birds 3–4 weeks old are the most        in the body (ascorbic acid     dehydroascorbic
commonly affected and flock mortality can be           acid + 2H). It participates in many processes,
nearly 20%. Ascites syndrome worldwide                including collagen synthesis, in epinephrine
costs about US$1 billion, with an average             synthesis from tyrosine and absorption of iron.
incidence of 4.7% in broiler flocks. Affected
birds are stunted and lethargic, with abdomi-                   O
nal enlargement and lack of appetite. Post-
mortem changes include marked right                                             O
                                                                                          O
ventricular dilation and hypertrophy, arterial
hypertrophy, ascites (serous fluid distension of                     O
the abdomen), pulmonary congestion and
oedema. Although the aetiology of ascites
syndrome is not completely known, it is                                   O           O
closely associated with right congestive heart                                                  (NJB)
failure. Other proposed contributing factors
include chronic oxygen deficits (housing at ele-       Ash         The mineral elements in a feed, or
vations of 3000 m), poor ventilation, high-           in biological tissue, measured by burning off
energy diets and salt, monensin or                    (‘ashing’) the organic matter and weighing the
furazolidone supplements. Of all these aetiolo-       residue (the ash). During ashing the organic
gies, those that contribute to rapid growth           matter in the material under test is oxidized
appear to be most closely linked to broiler           and minerals present in organic combination
ascites. A likely pathogenesis is that rapid          are changed to inorganic form. The measure-
growth and increased oxygen requirements              ment does not provide any information on the
lead to cellular oxygen deficits, pulmonary            specific elements present and ash may include
arterial hypertension, right heart failure, pas-      carbon from organic matter as carbonate
sive congestion of the abdominal organs and           when base-forming minerals are present in
ascites. A comparable syndrome with similar           excess. As with the measurement of any feed
nutritional and genetic contributing factors is       component, it is important that a representa-
seen in turkeys (round heart disease). Other          tive sample of the feed be used. The sample
toxins have also been shown to cause ascites          should be ground so that it will all pass
in birds. Severe ascites and oedema were              through a sieve with 1 mm diameter open-
reported in the 1960s when thousands of               ings; the sample should then be thoroughly
birds were poisoned with polychlorinated              mixed. A portion (2–3 g) is then dried to con-
38                                        Asian sea bass




stant weight at 103°C and the moisture con-        Aspergillosis             A fungal infection
tent determined. A portion (approximately 2        (mycosis) caused by a number of Aspergillus
g) of the dried feed is weighed into a crucible    spp. It is primarily a respiratory infection,
(nickel or porcelain) and placed in a muffle        especially in birds, but can affect the digestive
furnace. The temperature is raised, stepwise,      and reproductive tracts. Clinical findings
to 600°C. Ashing is allowed to proceed             include dyspnoea, gasping and polypnoea,
overnight (18 h), after which the crucible is      with microscopic evidence of fungal growth in
transferred directly to a dessicator, cooled and   affected tissues. Mastitis and abortion may
weighed and the ash content of the sample          occur in ruminants.                         (PC)
determined as the weight remaining.        (CBC)
                                                   Associative effects of foods                 The
Asian sea bass (Lates calcarifer)             A    effect of one food on the utilization of another
commercially important fish species farmed in       given with it; for example, the change in
several Asian countries and northern Aus-          digestibility of feed A attributable to the pres-
tralia. They belong to the family Centropomi-      ence of food B. Thus, a diet of equal parts of
dae and are commonly known as baramandi,           dry matter (DM) from coarse forage (DM
bhetki or giant sea perch. Asian sea bass are      digestibility 0.45) and a concentrate mix (DM
widely distributed in tropical and subtropical     digestibility 0.75) will not necessarily have a
areas of the Indo-Pacific region inhabiting a       DM digestibility of 0.6. This means that the
wide variety of freshwater, brackish and           metabolizable energy value attributed to an
marine habitats, including streams, lakes, estu-   individual feed is not necessarily its value
aries and coastal waters, but spawning only in     when used as a dietary component.
inshore marine waters. These predatory fish             Although associative effects occur in all
feed initially on small crustaceans and later      species, they are most important in ruminants
                                                   given concentrates and roughages together.
switch to fish. Juvenile sea bass may be canni-
                                                   Ruminants have a unique capacity to digest
balistic.                                (RMG)
                                                   cellulose, which allows them to consume poor
                                                   quality forages, such as crop residues. How-
Asparagine                     An amino acid
                                                   ever, to meet production targets for milk and
(NH2·CO·CH2·CH·NH2·COOH,             molecular
                                                   meat, the poorer the quality of the forage the
weight 132.1) found in protein. It contains
                                                   more necessary will be supplementary carbo-
both an amino and an amide group. It can be
                                                   hydrate feeds. Starch is rapidly fermented in
synthesized in the body from aspartic acid.
                                                   the rumen, causing a fall in the pH of the
                             O                     rumen liquor which, in turn, inhibits the cellu-
                                                   lose-fermenting enzymes. This depresses the
              O                  O                 breakdown of the cellulose contained in the
                                                   forage component of the diet. The effects will
                  N      N                         be greater when large amounts of concentrate
                                         (DHB)     are added and the forage component includes
                                                   mature grasses or crop residues. Adding con-
Aspartic acid          A dicarboxylic amino        centrates to an all-roughage diet can either
acid (COOH·CH2·CH·NH2·COOH, molecular              reduce or increase roughage intake, thus giv-
weight 133.1) found in protein. It can be syn-     ing a ‘substitution’ or ‘replacement rate’,
thesized in the body from oxaloacetate and an      defined as the change in roughage DM intake
amino donor.                                       per unit change in supplement DM intake.
                                                       True associative effects of foods are not
                             O                     easy to estimate, especially when mature for-
                                                   age or crop residues are a major dietary com-
              O
                                 O                 ponent. Such feeds are also generally deficient
                                                   in protein, thereby restricting the growth of cel-
                  O      N                         lulolytic bacteria and limiting the rate and
                                         (DHB)     extent of fibre digestion. Many of the starchy
                                          Automatic feeding                                        39




feeds will probably also contain protein degrad-     to Portugal in the eastern Atlantic and from
able in the rumen, which will tend to correct        Iceland and Greenland to Connecticut in the
this deficiency. To maximize rumen efficiency          western Atlantic. Eggs are spawned in late
from widely divergent foods, a combination of        autumn in freshwater streams. The fry hatch
rapid and slowly degradable proteins is needed.      the next spring and migrate to sea as smolts
The overall effect of combining forages and          after 1–8 years, depending upon latitude.
concentrates depends on the amount of each           Landlocked forms, living the full life cycle in
in the diet and on the quality of the forage         fresh water, also occur. Over 98% of Atlantic
(Galyean and Goetsch, 1993).                         salmon production worldwide is cultured.
    Many feeds are subjected to some form of                                                  (RHP)
physical processing. For grains, this is usually     See also: Salmon culture
either rolling or grinding, which allows the
rumen microbes easier contact with the grain         Attractants          Animals have innate pref-
contents, potentially resulting in an increase in    erences and aversions that can be used to
the extent and rate of digestion. With fodder,       make feeds attractive or repellent. Sweet
particularly      roughage,    whilst    grinding    flavours are commonly added to foods for
increases the surface area open to microbial         young animals, especially weaned piglets and
attack in the rumen, it removes the ability of       calves, as most animals have an innate prefer-
the animal to select the more nutritious plant       ence for sweetness. This flavour normally indi-
components. It can also make the feeds more          cates the presence of sugars which are readily
dusty and, therefore, less palatable.                available sources of energy. Even in the
    Positive associative effects of foods can        absence of such sugars, sweet flavours can
also be described as synergy, when the effect        induce animals to prefer foods containing
of the combination in the diet is greater than       them, as long as they do not also have antinu-
when either food is fed alone. Benefits can be        tritional factors such as high fibre, toxins, or
measured either as increased intake or as            nutritional imbalances. There is a belief (or
digestibility, or a combination of both.     (TS)    hope) that the inclusion of palatability agents
                                                     in a food will increase feed intake but this has
                                                     rarely been demonstrated to last for more
Reference
Galyean, M.L. and Goetsch, A.L. (1993) Utilization   than a few days. However, improving the
   of forage fibre by ruminants. In: Jung, H.G.,      attractiveness of one food when it is offered
   Buxton, D.R., Hatfield, R.D. and Ralph, J. (eds)   as a choice with one or more other foods may
   Forage Cell Wall Structure and Digestibility.     increase the short- and long-term preference
   USDA Agricultural Research Service and the US     for the flavoured food, depending on the rela-
   Dairy Research Center, Madison, Wisconsin.        tive nutritional value of all the foods on offer.
                                                                                                 (JMF)
Ataxia       A gait disorder in which the
movement of the animal is uncoordinated,             Atwater factors        These factors describe
typified by a swaying gait. It occurs in young        the metabolizable energy per gram of pro-
lambs and goat kids suffering from swayback,         tein, fat and carbohydrate (4, 9 and 4 kcal,
which is caused by copper deficiency.                 respectively). They are used in relation to
                                       (WRW)         human diets but are not commonly used in
See also: Copper; Gait disorders                     animal nutrition.                    (JAMcL)

Atherosclerosis         A condition in which         Automatic feeding          Mechanical meth-
atheromas, consisting of fatty material, occur       ods of providing feed to animals without
in the wall of arteries. It is not normally a        human intervention. For poultry, the most
problem in farm animals.               (WRW)         common form is the chain feeder, in which
                                                     compound feed, as mash or crumbled pellets,
Atlantic salmon (Salmo salar (L.))                   is conveyed round the house in an open-
A typically anadromous salmonid fish of the           topped metal duct. The feeder is controlled by
North Atlantic, ranging from the Arctic circle       a time clock so that animals can be fed at
40                                             Availability




Intensively reared poultry normally have both feed and water provided automatically.



fixed times, even when the stockman is not              feeding, predetermined amounts of meal or
available. This system allows equal access to          pellets are released into troughs, or on to the
feed by all the birds and is normally used for         floor of the pen. Liquid feeding systems are
breeding birds in lay and for layers during            also easily automated for both ad libitum and
rearing. Spin feeders distribute pellets over          restricted feeding. Electronic systems can be
the floor of the house. These are only suitable         used to control the intake of loose-housed ani-
for birds on restricted intake, such as broiler        mals such as dry sows: each animal has an
breeders during rearing, to ensure maximum             electronic tag which identifies it and triggers
distribution in the minimum time. With pan             the release of a predetermined amount of
feeders a central auger conveys feed into a            food when the animal enters the feeding sta-
number of suspended feeding dishes known               tion, but also denies it access if it has already
as pans. These can be adjusted to hold a               eaten all its allotted food.
given quantity of feed to ensure that all the              A similar system is commonly used for
pans receive the same amount of feed. As the           dairy cows, which are fed a predetermined
last pan empties, it triggers the drive mecha-         ration when they enter the milking stall. Fully
nism to refill the pans. Pans are the preferred         automatic systems are less common for other
system for ad libitum feeding, as in broiler           farm animals, though self-feeding and con-
houses.                                                trolled grazing are widely used for cattle and
    For pigs, the most usual system for ad libi-       sheep, and many systems of feeding are
tum feeding is similar to pan feeders, having          mechanized.                                   (KF)
an overhead conveyor that replenishes self-
feeders, which are hoppers in which the feed           Availability        ‘Availability’ and ‘bioavail-
flows by gravity into a trough to which the             ability’ are terms used to describe the percent-
pigs have continuous access. For restricted            age of a nutrient in a feed ingredient that is
                                                 Ayu                                                  41




digested, absorbed and metabolically utilized          tion, such as bone ash, haemoglobin, bone
so that it is available for growth, maintenance,       manganese concentration and liver accumula-
reproduction or production (milk, eggs, work).         tion of vitamin A, respectively.
‘Relative bioavailability’ refers to how well a           The term ‘available’ is used in a more
nutrient in a feed ingredient is used relative to      restricted sense in connection with lysine, to
a known standard. For example, a growth                describe the percentage of lysine in a feed
assay might be used to compare the utilization         ingredient that is not chemically conjugated in
of threonine in soybean meal to that of threo-         ways that make it unusable in metabolism.
nine fed as pure L-threonine, which is com-            ‘Available lysine’ used in this sense does not
pletely available. This is commonly a slope            include any measure of its digestibility.
ratio assay, which involves feeding at least                                                     (DHB)
three doses of L-threonine in the linear area of       See also: Nutrient bioavailability
the growth response curve (usually between
40 and 70% of the requirement). A criterion            Available: see Availability; Bioavailability
of response such as weight gain or protein
accretion is then related to supplemental thre-        Avidin        A natural glycoprotein found in
onine intake to generate a standard slope.             egg white. It tightly binds biotin and has been
Graded doses of soybean supplying similar              shown to induce biotin deficiency in chicks
amounts of threonine are also fed and again            and rats when fed raw. There are also anec-
the response is related to threonine intake.           dotal reports of avidin-induced biotin defi-
The slope for soybean meal threonine is                ciency in other livestock. As avidin is easily
divided by the slope for standard L-threonine          denatured by heat, cooking or biotin supple-
to provide an estimate of relative bioavailabil-       mentation is recommended when animals are
ity. A similar procedure can be used with a            fed raw egg whites.                       (BLS)
single level of soybean meal. In this assay, the
resulting weight gain is inserted into the             Ayu (Plecoglossus altivelis)              Also
regression for free threonine to give the              known as ‘sweet fish’ or ‘pond smelt’, a mem-
bioavailable threonine intake. This value is           ber of the salmon family, native to East Asia.
then divided by the actual measured threonine          This anadromous fish spawns in fresh water
intake to arrive at an estimate of relative            and after a year returns to the sea, where it
bioavailability.                                       feeds on benthic organisms such as diatoms
    With amino acids, relative availability deter-     and blue-green algae. Ayu are cultured in
mined by growth assay should be similar to             either freshwater or seawater ponds and their
true digestibility measured directly. However,         optimum water temperature range is
growth assays do not work well for many                15–25°C. Larvae hatched in captivity require
nutrients, such as phosphorus, iron, man-              acclimation to sea water before being fed live
ganese and vitamin A. For such nutrients,              food organisms such as rotifers and artemia.
response criteria are needed that respond lin-         The average market size is 50–150 g.
early to graded doses of the nutrient in ques-                                                  (SPL)
                                                      B

B-complex vitamins            The B-vitamin                 Bagasse            The fibrous residue remaining
complex is a group of eight water-soluble                   after sugarcane has been milled and the juice
vitamins which, like all vitamins, must be                  extracted. It is normally used as a fuel in sugar
provided in sufficient amounts in the diet.                  mills, in the manufacture of fibreboard or
They are thiamine, riboflavin, niacin, pyri-                 paper, as animal bedding and as a ruminant
doxine, folate, biotin, pantothenic acid and                feed. Untreated bagasse has a very low
vitamin B12. Each of these is intimately                    digestibility but this can be improved by treat-
involved as a coenzyme or co-substrate in                   ment with high-pressure steam or alkali
one or more reactions in cellular metabo-                   (sodium hydroxide).                          (EO)
lism. For example, thiamine is converted to                 See also: Sugarcane
thiamindiphosphate and pantothenic acid to
coenzyme A. Co-factors such as these are                    Bakery products           Wastes from bread,
                                                            cake, biscuit and pasta making. Typically
not changed as a result of the chemical
                                                            these are high in starch and oil but composi-
reaction in which they participate. These
                                                            tion varies and each product should be
enzyme co-factors play critical roles in
                                                            analysed before it is used in animal diets.
metabolism. Because of their participation
                                                            These products can be fed to ruminants and
in cellular metabolism they are widely dis-
                                                            non-ruminants but their high levels of oil can
tributed in nature.                    (NJB)                reduce rumen fibre degradation rates. They
                                                            are an excellent source of energy but the qual-
Backfat          The layer of subcutaneous fat              ity of the protein and starch can be reduced
lateral to the spine. The thickness of this layer           by heat processing. Fresh products are very
is a good predictor of the total body fat con-              palatable but should be used before they
tent of the carcass and this measure is often               become mouldy or rancid. Palatability may be
used in grading the carcasses of pigs, for                  reduced when the products are dried and
which a common point of measurement is the                  ground. The main factors limiting the use of
P2 position, 6.5 cm lateral to the spine at the             bakery products are the high oil content and
level of the last rib.                     (SAE)            risk of contamination from packaging. Their
                                                            high oil concentrations can reduce the vitamin
Bacteria: see Gastrointestinal microflora                    E level of the diet.                     (JKM)



Composition of bakery products.

                                                   Nutrient composition                          Energy
                                                       (g kg 1 DM)                            (MJ kg 1 DM)

                      Dry matter      Crude
                       (g kg 1)       protein         Oil         Starch           Sugar    MER         MEP

Bread                  650–680       120–125         30          260–280           75–80      14         16
Bakery waste           500–890        10–150       10–250        200–600           50–250    9–19       18.5
Confectionery          800–900         5–200       10–250          0–100          150–250   12–18        –

MEP, metabolizable energy for poultry; MER, metabolizable energy for ruminants.


                                                                                                             43
44                                               Bale




Bale          A large bundle of material bound       protein content is highest in Dencrocalamus
with twine or wire. There are four basic types       strictus. In bamboo leaves, the dry matter
of bale: (i) the traditional small rectangular hay   (DM) is 550–600 g kg 1 and the nutrient
bale 0.35 m         0.45 m       0.9 m weighing      composition (g kg 1 DM) is crude protein
20–30 kg; a small round bale 0.45 m                  180–190, ether extract 5–40, crude fibre
0.60 m; (iii) a large square bale 1.5 m              220–290 and ash 118–170, with MER of
1.5 m        2.4 m weighing 400–700 kg; and          11.3 MJ kg 1 DM.                       (JKM)
(iv) a large round bale 1.2 m        1.2 m weigh-
ing 400–700 kg. For ensilage, bales are
                                                     Key reference
either wrapped in polythene film or placed
                                                     Bhargava, A., Kumbhare, V., Scrivastava, A. and
into polythene bags and sealed, to ensure
                                                        Sahai, A. (1996) Bamboo parts and seeds for
anaerobic conditions.                         (DD)      additional source of nutrition. Journal of Food
                                                        Science and Technology 33, 145–146.
Balenine          -Alanyl     3-methylhistidine,
the dipeptide formed of 3-methylhistidine with
                                                     Banana (Musa                 paradisiaca L.)
  -alanine. It has also been called ophidine.
                                                     Bananas and plantains (cooking banana) are
Protein-bound histidine in muscle is methyl-
                                                     grown in the tropics as staples for human
ated in the 3 position and is released as free       consumption and for export. By-products fed
3-methylhistidine when actin and myosin are          to livestock are surplus and reject fruit, peels,
broken down in normal protein turnover.              leaves and pseudostems.
Other compounds of similar structure are                 Banana (and plantain) fruit are mainly
carnosine ( -alanylhistidine) and anserine ( -       starch (c. 70% in dry matter), some of which
alanyl 1-methylhistidine). Balenine is found in      is converted to sugars with ripening. As pro-
the blood and tissues of pigs.                       tein (< 4% in dry matter), minerals (especially
                                                     Na) and fibre contents are low, supplementa-
                    O         O                      tion is necessary when feeding. Normal usage
                                                     is for pigs; supplementation with a protein
                     N       H                       source of appropriate amino acid spectrum is
                                                     important. Ripe bananas promote higher
                                                     growth than green ones, probably because of
                    O                                ‘active’ tannins in unripe bananas. Cooking
     N                                 N
                                                     slightly improves green bananas for pigs.
                                 N
                                                     Chopped green bananas are highly palatable
                                                     for cattle, but less so for sheep and goats. For
                                            (NJB)
                                                     ruminants, urea is a suitable (and less expen-
                                                     sive) source of much of the supplemental pro-
Bamboo           Plant of the family Gramineae       tein. Banana-based diets require fibre
(grasses), chiefly of warm or tropical regions.       supplementation to ensure normal rumen
Bamboos are the largest grasses, sometimes           function. Bananas can be ensiled. Peels can
reaching 30 m in height. The stalks are round        be fed when ripe, but not green. Leaves are
with evergreen or deciduous leaves. Uses             fed to ruminants during scarcities, but low
include wood for construction, paper produc-         protein and high tannin make for low
tion and fuel. The sprouts are eaten as food.        digestibility and low intake. The pseudostem
Bamboo may be fed to ruminants either fresh          of banana comprises fleshy leaf sheaths that
or as silage of boiled bamboo shoot shell.           surround the stem, and also stem after the
Bamboo has a high potential nutritional value        fruit is harvested. It is high in moisture (>
and rumen degradability. The addition of             90%) and is fed, freshly chopped, to rumi-
wheat bran increases the rumen degradability         nants and pigs. The dry matter is low in pro-
of dry matter and protein. In bamboo seed,           tein (< 4%) and mostly nitrogen-free
the carbohydrate and vitamin C contents are          extractives (c. 60%). Ensiling is also possible.
highest in Bambusa arundinacea and the                                                            (EO)
                                                 Barley                                                45




Key references                                         malt culms (or malt sprouts) and brewers’
Babatunde, G.M. (1992) Availability of banana and      grains. Malt culms comprise the dried rootlets
   plantain products for animal feeding. In: Roots     and sprouts of germinated barley grains pro-
   and Tubers, Plantains and Bananas in Animal         duced in the malting process. Brewers’ grains
   Feeding. FAO Animal Production and Health           are the spent grains from the mashing and fil-
   Paper No. 95. Food and Agriculture Organiza-
                                                       tration and are widely used to replace both
   tion, Rome, pp. 251–276.
Gohl, B. (1981) Tropical Feeds. Food and Agricul-
                                                       forage and concentrates in the diets of rumi-
   ture Organization, Rome, 515 pp.                    nants. The production of malt whisky from
                                                       the distillation of barley malt alone or a mix-
                                                       ture of cereals (grain distillation) produces a
Barley         Barley (Hordeum sativum) is a           number of wet and dry by-products for use in
member of the Gramineae (grass) family. It is          the animal feed industry. These include dis-
cultivated primarily for its grain, which is used      tillers’ wet spent malt (malt draff) or grains
for human and animal food. The grain (ker-             (grain draff) and light grains (dried draff), pot
nel) comprises the seed and pericarp (seed             ale syrup, malt distillers’ dried solubles, super-
coat) and is surrounded by a hull (or husk) rep-       draff and distillers’ (malt or grain) dark grains.
resenting 0.1–0.15% of the grain weight. The           Also produced are malt culms (dried rootlets
hull is composed of two structures, the palea          and shoots) and malt residual pellets, consist-
and lemma, collectively referred to as glumes,         ing of pelleted malt culms, thin and broken
and these fuse with the outer coat of the              grains (after dressing) with barley hulls and
developing grain to produce a covered kernel.          dust. Barley feed is the by-product arising
The chemical composition and nutritive value           from the preparation of pearl barley for
of barley grain (see table) is influenced by the        human consumption. This comprises three
presence of the hull.                                  grades of dust produced during processing
    Livestock feeding represents the single            and contains approximately 140 and 100 g
most important market for the world’s barley           kg 1 dry matter (DM) of protein and fibre,
production (~ 50% of the total), the remain-           respectively. Dried brewers’ grains and dis-
der being used for human food consumption              tillers’ dark grains can be fed at a level of 20%
and for malting purposes. Barley contains lit-         diet DM in growing cattle and dairy cows and
tle of the gluten protein whose elastic proper-        10% diet DM for calves and sheep. Their high
ties are important in bread making. Barley             unsaturated fatty acid contents may cause a
flour is therefore used to make unleavened or           reduction in fibre degradation in the rumen
flat bread, and porridge in North Africa and            and a depression in feed intake. Copper toxic-
parts of Asia, where it is a staple food grain.        ity may arise from feeding distillers’ grains to
    By-products of barley arise mainly from the        sheep. For pigs, the use of distillers’ grains is
brewing, distilling and pearl barley industries.       generally restricted to feeding to sows, due to
Brewing gives rise to two main by-products:            the high fibre content.




Barley is grown primarily for animal feeding and brewing: by-products of brewing are also used for animal
feeding.
46                                               Basal metabolism




Chemical composition and nutritive value of barley grain and barley by-products (as g kg   1   dry matter unless
specified). (After MAFF, 1990.)

                                                                                   Energy value (MJ kg 1 DM)
                            DM                                            GE
Feed type                 (g kg 1)    CP      Starch       NDF       (MJ kg 1 DM) Ruminantsa Pigsb     Poultryc

Barley grains
All seasons                 864      129       562         201            18.5          13.3         15.4       –
Winter                      857      130       585         178            18.5          13.5         15.4      14.3
Spring                      869      128       572         207            18.5          13.2         15.5       –

Barley by-products
Fresh brewers’ grains       250      218        38         619            21.3          11.5           –           –
Draff                       248      211        18         673            21.5          10.2           –           –
Distillers’ dark grains     907      275        26         420            21.3          12.2           –           –
Malt culms                  906      290        57         556            18.9          11.1           –           –
Pot ale syrup               483      374         –           6            20.0          15.4           –           –

Forages
Straw (all seasons)         867      41.5       10.9       811            18.4             6.4         –           –
Straw (spring)              862      42.6       17.8       811            18.5             6.6         –           –
Straw (winter)              874      37.6        2.2       809            18.3             6.2         –           –
Whole-crop silage           394      90.3      234         575            19.1             9.1         –           –
aAs metabolizable energy; b as digestible energy; c apparent metabolizable energy (corrected to zero).
CP, crude protein; DM, dry matter; GE, gross energy; NDF, neutral-detergent fibre.


   In addition to the use of barley and barley               that the subject must be in a thermoneutral
by-products in livestock diets, barley may also              environment, have not eaten for 12 h and be
be grown as a forage crop or ensiled as a                    lying down but not asleep; usually it is mea-
whole-crop forage. Barley straw is also pro-                 sured soon after the subject has awoken from
duced following harvesting of the grain and                  a night’s sleep. Compliance with these condi-
can be utilized for feed purposes.         (ED)              tions demands a cooperative subject and is vir-
                                                             tually impossible with animals. Nevertheless,
                                                             the concept of basal metabolism still provides
Further reading                                              a useful starting point, not only for interbreed
Givens, D.I., Clarke, P., Jacklin, D., Moss, A.R. and        and interspecies comparisons, but also for
   Savery, C.R. (1993) Nutritional Aspects of                consideration of the additional energy needed
   Cereals, Cereal Grain By-products and Cereal
                                                             for food ingestion, digestion, lactation, preg-
   Straws for Ruminants. HGCA Research
                                                             nancy, exercise and environmental discomfort,
   Review No. 24. HGCA, London, 180 pp.
                                                             all of which increase metabolic rate above the
MAFF (1990) UK Tables of Nutritive Value and
   Chemical Composition of Feedingstuffs.                    basal level. Nor is BMR the minimum level; the
   Rowett Research Services, Aberdeen, UK, 420               rate drops, for example, during sleep and in
   pp.                                                       starvation. Metabolic rate is higher in growing
McDonald, P., Edwards, R.A., Greenhalgh, J.F.D.              animals and productive adults than in those fed
   and Morgan, C.A. (1995) Animal Nutrition,                 maintenance rations, and although it is obvi-
   5th edn. Longman, Harlow, UK, 607 pp.                     ously greater in large than in small animals,
                                                             the latter have a much greater BMR per unit
Basal     metabolism          The irreducible                weight. Brody’s (1945) classic graph, repro-
energy cost of maintaining the body during                   duced here, shows that when body weights
complete rest. It was originally intended to                 and ‘basal’ metabolic rates are plotted on a
provide a standard condition of measurement                  double logarithmic grid, the results from
for human subjects, which would make possi-                  mature animals of different species ranging
ble comparisons between individuals, ages,                   from mice to elephants fall close to a straight
sexes, races, social groups etc. The conditions              line. Brody’s regression equation, converted
for measuring basal metabolic rate (BMR) are                 into SI units, may be written as:
                                                                                       Bean                                                                   47




                                                                                Body weight (lbs)
                                                           0.1         1.0         10      100                 1000      10,000

                                                         Cal = 39.5 lb0.734                    horses
                                                                                                            elephants            100,000
             (cal day–1 and cal kg–1 day–1)                                                  dairy bulls
                                              10,000     BTU = 156.8         lb0.734        beef cows
                                                                                          beef steers              beef steers
                                                                                                                 dairy cows
                                                         Cal = 70.5 kg0.734                ponies
                   Basal metabolism




                                                                                                                                           Basal metabolism
                                                                                                                                 10,000
                                                                                        humans                 swine




                                                                                                                                             (BTU day–1)
                                               1000                                                    sheep
                                                                          goose                 dogs
                                                                         cat                                                     1000
                                                                   rabbits                    20% deviation lines
                                                                   ducks                domestic fowl
                                                100         guinea pigs
                                                             pigeons                          cal k
                                                       canaries                                    g –1 =
                                                                                rats                        70.5 –0.2            100
                                                        sparrows                                                        66
                                                 10                   dove
                                                               mice                                                            20
                                                   0.01       0.1            1.0        10            100        1000        5000
                                                                                Body weight (kg)
Brody’s (1945) graph relating basal metabolism of mature species to body weight.

    BMR = 3.41 (weight in kg)0.734 Watts                                                     Brody, S. (1945) Bioenergetics and Growth. Rein-
    or                                                                                          hold Publishing Co., New York.
    BMR = 295 (weight in kg)0.734 kJ/24h.
    It is emphasized that the ‘basal’ metabolic                                              Beak         In birds, synonymous with ros-
rates considered by Brody do not fulfil the con-                                              trum or bill. The beak includes the upper and
ditions as originally defined for humans. They                                                lower projecting mandibles, which are cov-
probably most nearly represent either fasting                                                ered by horny layers of keratinous tissues and
metabolism of animals that are free to stand or                                              grow continuously. When food is gathered by
lie at will but not recently fed, or resting                                                 the beak, it is mixed with saliva containing
metabolism of normally fed animals lying                                                     digestive enzymes secreted from glands
down. The interspecies comparison may not                                                    around the mouth.                      (MMax)
be so exact as it at first appears from Brody’s
graph; the dashed lines on either side repre-                                                Bean          Beans include field bean (Vicia
sent 25% divergences of BMR from the pre-                                                    faba, L. spp.), horse bean (V. faba var.
dicted values. More recent measurements                                                      equina Pers) and broad bean (V. faba var.
suggest that for some species BMR tends to be                                                minuta (Alef ) Mansf.). Beans are legumes
consistently different from the values predicted                                             mainly grown for human consumption but
by the Brody relationship (approximately 20%                                                 some varieties are grown for animal feed.
higher in cattle and 20% lower in sheep).                                                    There are winter and spring varieties of bean
Brody’s regression does, however, demon-                                                     which have contrasting agronomic character-
strate that tissue of small animals is metaboli-                                             istics suitable for different sites, but yield and
cally more active than that of large ones; BMR                                               harvest date differences are small. Beans are
per unit of body weight of mice is 25 times as                                               a good source of protein and energy, with
great as that for elephants. The exponent                                                    high levels of lysine, but they are low in
0.734 found by Brody is frequently rounded to                                                methionine and cysteine. Spring varieties are
0.75, and body weight to the power 0.75,                                                     higher in protein than winter varieties.
known as metabolic body size, is often used                                                  Beans are rich in thiamine and phosphorus
for interspecies comparisons.           (JAMcL)                                              and are often used to replace peas in animal
                                                                                             diets. They contain tannins and trypsin
Further reading                                                                              inhibitors, which may reduce protein
Blaxter, K.L. (1989) Energy Metabolism in Ani-                                               digestibility, though new low-tannin varieties
   mals and Man. Cambridge University Press,                                                 are grown. Urease, phytates, haemagglu-
   Cambridge, UK.                                                                            tinins and glucosides are regularly present in
48                                       Beckmann process




raw beans. These anti-nutritional factors limit     and Limousin. These all originated in Europe
dietary inclusion rates, particularly in diets      but, as they have been exported worldwide,
for non-ruminants, but they can be inacti-          further selection for local conditions (espe-
vated by heat processing. Field beans can be        cially hot climates) has created a number of
included in dairy, beef and ewe diets at 20%        sub-breeds. Whilst under ideal temperate con-
of total diet, in finisher pig and sow diets at      ditions these are far better suited to the pro-
10%, in grower pig diets at 7.5%, and in            duction of beef than many general-purpose
lamb, calf and breeder and layer chicken            native cattle, under tropical conditions and
diets at 5%. A blend of extruded beans and          stresses they are not as productive, and may
full-fat rapeseed (50:50) known as ‘Extrupro’       be subject to devastation in situations such as
is used as a high-energy and high-protein           drought. To avoid this, cross-breeding of
supplement for all ruminants. The dry matter        imported improved breeds with local cattle
(DM) content of spring beans is 840–880 g           can be used, or where conditions are particu-
kg 1 and the typical nutrient composition (g        larly unfavourable the improvement of the
kg 1 DM) is crude protein 210–290, crude            local cattle is normally the best option. A
fibre 70–90, ether extract 10–25, ash                good example of this is the Chinese Yellow
25–41, neutral detergent fibre 100–211,              Breed which has an excellent feed conversion
starch 300–400 and sugars 15–55, with               ratio and can survive on poor quality feeds
MER 10.5–14.0 and MEP 13.5 MJ kg–1.                 such as rice straw which is plentiful in China.
                                        (JKM)       Many improved breeds cannot be productive
                                                    on such a poor diet so improvements in pro-
Beckmann process               This technique,      ductivity depend on selection within the
named after the German chemist Ernst Beck-          breed, supported by limited cross-breeding
mann, uses alkali to hydrolyse the ester bonds      programmes.
between lignin and cell wall polysaccharides to         Large scale cross-breeding programmes
improve the degradability of cereal straws.         have created tropical beef breeds such as the
Cereal straw is soaked for up to 2 days in a        Brahman, Droughtmaster, Brangus and Santa
dilute (1.5%) solution of sodium hydroxide          Gertrudis. Brahman were created by selecting
and then washed to remove excess alkali,            and crossing productive tropical cattle, whilst
prior to feeding.                        (FLM)      the other three were developed by cross-
See also: Alkali treatment                          breeding the Brahman with European breeds
                                                    such as Shorthorn and Aberdeen Angus.
Beef        Meat from cattle, mostly from spe-          Animals used for beef production normally
cialized beef breeds.                               come from one of two sources: specific beef
                                                    breed dams mated to beef breed sires; or
Beef cattle          Cattle used to produce         dairy cow dams mated to beef breed sires.
meat. Beef cattle are produced either for sale      Animals that are 100% dairy or of multipur-
or for on-farm consumption throughout most          pose breeds can also be used for beef,
of the inhabited world, except in areas of          depending on the circumstances and the avail-
Africa infested with tsetse fly where try-           ability of bloodstock, though with poorer pro-
panosomiasis prevents all but a few resistant       ductivity.
breeds from being kept, and areas where the             The systems in which beef cattle are kept
Hindu religion is practised (India) as cattle are   vary from extensive ranches to intensive feed-
considered to be sacred and are not eaten.          lots. In between these extremes are other sys-
   Ideally beef cattle are large, well-muscled      tems such as suckler cow production, family
animals, with good conformation (i.e.               farm fattening of store cattle, and smallholder
muscling around the shoulders and especially        (backyard) rearing. Ranches are found where
the hind quarters), fast rates of growth, and       land is cheap and feeds are of low nutritive
good feed conversion ratios. These attributes       value, whereas feedlots are found where feed-
are found to varying degrees in most specialist     stuffs are cheap (often near to agri-industrial
beef cattle breeds, which include Aberdeen          wastes) but land is expensive (often due to its
Angus, Hereford, Belgian Blue, Charollais           location near to major cities). Backyard pro-
                                           Bicarbonate                                            49




duction occurs where families fatten a small       epinephrine is instead thought to act via -
number of cows on whatever vegetation,             adrenergic receptors (the other major class of
wastes and residues are available.                 catecholamine receptors). The -adrenergic
    Typical feeding regimes for beef cattle        receptors are further broken down into three
combine fodder, either fresh or preserved,         classes: 1, 2 and 3. There are both
with some concentrates. Fresh, grazed grass is     broad-based and selective pharmacological
used where the climate permits, with such          agonists for each type. The classic -agonist is
cereals and by-products as are available and       isoproterenol. Synthetic -adrenergic agonists
cost-effective. Straw can also be used as a        such as clenbuterol, cimaterol and rac-
bulk feed if the rest of the ration is designed    topamine have major effects on the growth
to cover its deficiencies. It is important not to   and metabolism of skeletal muscle and adi-
feed too much concentrate which causes fat         pose tissue of food animals.            (NJB)
to be laid down rather than lean tissue. The
shorter the production cycle the greater the        -Alanylhistidine: see Carnosine
risk of this. However, in some cultures fatty
meat is preferred.                        MMal     Beta-oxidation          The metabolic processes
                                                   involved in catabolism of free fatty acids. Even-
Beet, fodder: see Fodder beet                      chain fatty acids are cleaved into a common
                                                   two-carbon intermediate, acetyl-CoA. Odd-
Beet, sugar: see Sugarbeet                         chain fatty acids produce mainly two carbon
                                                   units (acetyl-CoA) but the terminal three-carbon
Behaviour, feeding: see Feeding behaviour          unit is released as propionyl-CoA. Since this
                                                   process occurs in the mitochondrion, all cells
Behenic acid          Docosanoic acid, a satu-     (with the exception of the mature mammalian
rated long-chain fatty acid, CH3·(CH2)20           erythrocyte) are thought to catabolize fatty acids
·COOH, shorthand designation 22:0. It is           in this way.                                (NJB)
found in oils such as groundnut and rapeseed
oils, some milk fats and marine animal oils.       Betaine        A water-soluble compound,
                                                           +
                                         (NJB)     (CH3)3·N·CH2·COO–, widely distributed in
                                                   plant and animal tissues. In metabolism,
Benzoic acid          C7H6O2, an unsaturated       betaine is derived from the oxidation of
six-carbon ring with a carboxyl carbon             choline in a two-step process. One of the
attached. It is found in berries and gum ben-      methyl groups of betaine can be used by the
zoin and is used as a food preservative. Ben-      liver enzyme betaine homocysteine methyl-
zoic acid is not apparently catabolized by         transferase to methylate L-homocysteine to
animals but is conjugated with glycine in the      form L-methionine. The remaining two methyl
liver to form hippuric acid, which is excreted     groups of betaine are converted into one-car-
in urine. Hippuric acid makes up a greater         bon units of the folate system.        (NJB)
fraction of urinary nitrogen in grazing rumi-
nants than in simple-stomached animals.            Bicarbonate        Bicarbonate is formed in
                                         (NJB)     animals from CO2 produced in the catabolism
                                                   of carbohydrates, fats and amino acids. The
Beta agonists          Beta agonists ( -adren-     carbon dioxide produced is dissolved in water
ergic agonists) are substances that activate -     and, with the aid of the erythrocyte enzyme
adrenergic receptors. They include both            carbonic anhydrase, carbonic acid (H2CO3) is
the naturally occurring catecholamines (i.e.       produced. Carbonic acid can dissociate into
dopamine, norepinephrine and epinephrine)          bicarbonate HCO3– and hydrogen H+ ions.
and synthetic compounds that are structurally      The carbonic acid–bicarbonate system
similar to them. Epinephrine appears to be         (H2CO3 → H+ + HCO3–) is one of the three
the natural agonist for these receptors. Nor-      major blood buffering systems. This system
epinephrine also activates them but only at        differs from the haemoglobin and protein
high (pharmacological) concentrations. Nor-        buffer systems because the blood concentra-
50                                                Bifidobacteria




tion of CO2 is maintained and is continually                Binding agents            Materials added to com-
replenished. It is controlled by respiratory rate           pound feed at relatively low rates of inclusion
and the plasma concentration of HCO3– is                    (0.05–2.5%) to increase the durability and
controlled by the kidney. Bicarbonate plays a               hardness of the pellets. Improved durability
major role in maintaining the pH of blood                   allows further mechanical handling during
near 7.4.                                  (NJB)            transport, transfer into storage systems and
                                                            feeding. Hardness is important to avoid pellet
Bifidobacteria:                  see Gastrointestinal        destruction due to pressure when stored in bulk
microflora                                                   bins. It is not always correlated with durability.
                                                                Binding agents are also thought to increase
Bile        Bile is made in the liver, stored in            press capacity and pelleting efficiency as some
the gallbladder and secreted into the small                 allow more fat and steam to be added to the
intestine at the level of the duodenum. It con-             meal during conditioning. The table below
tains sodium and potassium salts of the bile                gives common binding agents.                  (MG)
acids cholic acid and chenodeoxycholic acid.
The salts of deoxycholic acid and lithocholic               Binding proteins            Proteins that specifi-
acid are also found in bile but these bile acids            cally interact with some other molecule (e.g.
are the result of microbial metabolism of                   another protein) or atom (e.g. a mineral).
cholic acid and chenodeoxycholic acid,                      Binding proteins are varied in their function.
respectively, in the intestinal contents. The               They can be involved in a variety of physio-
bile pigments, bilirubin and biliverdin, are                logical functions. Interaction of a binding pro-
products of haemoglobin degradation. Limited                tein with its ligand can result in a
amounts of inorganic salts, fat, lecithin, fatty            conformational change in the binding protein
acids and cholesterol are also found in bile.               that alters its function. Enzymes can be con-
The bile acids are conjugated with one of two               sidered specific binding proteins for substrates
amino acids: glycine or taurine. These conju-               and, when they bind them, cofactors.
gates are referred to as glycocholic and tauro-
cholic acids. Bile acids can be reabsorbed
from the intestinal tract at the level of the               Regulation of gene expression (DNA or RNA
ileum and returned to the liver by the portal               binding proteins)
circulation, from which they can be secreted                Transcription factors can regulate the produc-
again in bile; this is called the enterohepatic             tion of messenger RNA (mRNA) by turning
circulation. Bile enhances lipid digestion due              on or off the expression of specific genes.
to the formation of fatty acid-containing                   RNA binding proteins can influence the pro-
micelles that can diffuse through the unstirred             duction of mature mRNA by affecting RNA
water layer on the mucosal surface where the                splicing, polyadenylation (addition of multiple
fatty acids are subsequently taken up by the                adenosine residues to an mRNA precursor) or
enterocytes.                               (NJB)            RNA transport. In addition, RNA binding pro-


Binding agent                                                                                   E number

Citric acid                                                                                     E330
Sodium, potassium and calcium stearates                                                         E470
Silicic acid (precipitated and dried)                                                           E551a
Colloidal silica                                                                                E551b
Kieselguhr (diatomaceous earth, purified)                                                        E551c
Calcium silicate (synthetic)                                                                    E552
Sodium aluminosilicate (synthetic)
Kaolin and kaolinitic clays (free from asbestos and containing at least 65% complex hydrated    E559
   aluminium silicates whose main constituent is kaolinite)
Natural mixtures of steatite and chlorite free of asbestos                                      E560
Vermiculite
Lignosulphonates                                                                                E565
                                           Bioavailability                                          51




teins are critical in mRNA translation into pro-    or nutrient to a standard, which is usually the
tein. RNA binding proteins are critical for the     nutrient in its pure and fully available form.
function of the ribosome, for putting the           The test may use a single measurement (mean
proper amino acid on to a specific tRNA              ratio method) or a set of several intakes of the
(aminoacyl tRNA synthetases) for binding to         standard (slope ratio assay). In the simplest
specific regions of mRNA.                            slope ratio assay, a purified or semi-purified
                                                    standard such as reagent grade compound,
Cell signalling                                     crystalline amino acid, etc., is fed in a series
Protein–protein interactions are critical for       of diets to give three or more levels of a nutri-
                                                    ent that produce a linear increase in the cho-
transmission and decoding of hormone signals
                                                    sen criterion (e.g. growth) in response to
by cells. Examples include binding of hor-
                                                    increasing amounts of the nutrient. The test
mones to their receptor (insulin binding to the
                                                    material is also incorporated into one or more
insulin receptor) and for the interaction of the
                                                    diets at levels that would be expected to yield
hormone receptors with other proteins that
                                                    a linear response but are less than the known
transmit the signal into specific cellular
                                                    or estimated optimum dietary level for maxi-
actions.
                                                    mal response. Provided that there is a linear
                                                    relationship between the nutrient intake (x)
Transport of compounds                              and the animal’s response (y) with both the
Binding proteins exist for certain vitamins (vit-   test and the standard nutrient sources, the
amin D binding protein) or minerals (transfer-      relationships can be expressed as ytest = atestx
rin) and are important in moving such               + btest and ystd = astdx + bstd, respectively,
compounds between organs and cells or, in           where atest is the slope and btest is the intercept
some cases, within cells.                           of the regression equation with the test source
                                                    and where astd and bstd are the slope and inter-
                                                    cept with the standard nutrient source. It is
Cell structure
                                                    also assumed that the two lines generated by
A variety of filament systems organize the
                                                    these equations intersect at 0,0. To ensure the
cytoplasm of cells and can alter cell shape. An
                                                    validity of the assay, this assumption is tested
example is microtubules (MTs) made of the
                                                    in the analysis of the results. Therefore the
protein tubulin. MTs form hollow fibres that
                                                    ratio of the slopes, 100 atest/astd, is an esti-
are used to transport proteins to different
                                                    mate of the bioavailability of the test nutrient,
locations in the cell. MTs are also important in
                                                    when the bioavailability of the standard is
chromosome separation during cell division. A       assumed to be 100% (Littell et al., 1995).
variety of MT binding proteins exist that can           Variations of the slope ratio method include
alter MT function.                        (RSE)     the standard curve and mean ratio assays. In
                                                    the former case, several data points are gener-
Bioavailability          That proportion of a       ated with the standard nutrient source to obtain
dietary nutrient that is absorbed and may then      a standard linear response. A single level of the
be utilized by an animal for physiological func-    test feed is given such that the intake of the
tion(s). The method of assessing bioavailability    nutrient falls within the range of the standard.
depends on the species and its physiological        The response value (ytest) is then compared
state. The animals that are of most interest to     with the value expected from the same amount
nutritionists are usually those that are growing    of pure nutrient, using the regression equation
or producing (meat, milk, eggs, etc.). Conse-       for the standard source. Thus, bioavailability =
quently, growth, efficiency of feed utilization,     100 ytest /(astd xtest ). In some cases, a direct
output of milk or eggs or changes in tissue         comparison of a test source of a nutrient is
concentration of some nutrient (e.g. calcium        made to a standard source of that nutrient,
in bone) are frequently chosen as parameters        each having only one data point. In this case,
of measurement.                                     the validity of the assay is heavily dependent on
   In most bioavailability assays the chosen        the amount of the nutrient in the test source
parameter is used to compare a test feedstuff       compared with the standard. If the amount is
52                                               Biogenic amines




small, the assay is usually less accurate. It is               Journal of the World Aquaculture Society 30,
important to recognize that, in addition to the                58–64.
nutrient of interest, the test feed may contain
other constituents that contribute, positively or           Biogenic amines             Decarboxylation prod-
negatively, to the animal’s response. This diffi-            ucts of amino acids with hormone-like actions.
culty can be minimized by arranging that the                Histamine is formed by decarboxylation of L-
diets used to establish the standard curve are              histidine. Histamine affects cells by binding to
deficient only in the nutrient being tested and              histamine receptors (H1, H2 or H3) found in
that antinutritional factors in the test feed are           peripheral tissues and the brain. Tyrosine is
inactivated.                                                converted to L-dopa (dihydroxyphenylalanine),
    Sometimes, the bioavailability of certain               which is decarboxylated to dopamine which, in
nutrients for fish is more easily estimated by               turn, can be hydroxylated to become norepi-
conducting controlled digestibility trials.                 nephrine. These processes are carried out in
Although this does not technically fulfil the                catecholamine-secreting neurons and in the
definition of bioavailability it is useful because,          adrenal medulla. The products act on - and β-
for many nutrients, digestibility is the main               receptors. Tryptophan is hydroxylated to 5-
component of availability.                                  hydroxytryptophan which is decarboxylated to
    More accurate estimation of the true                    form serotonin (5-hydroxytryptamine), which
digestibility of a given nutrient may be deter-             is found in the brain and in serotonergic neu-
mined by the use of isotopes. The method has                rons. It has its effect through cellular serotonin
been particularly useful in determining true                receptors. In the pineal gland, serotonin is
absorption of various essential minerals, espe-             converted to melatonin. The neurotransmitter
cially of trace minerals. Ideally the source of               -aminobutyrate is derived from the decar-
the nutrient in question is one in which the                boxylation of glutamic acid.                 (NJB)
nutrient has been biosynthesized in the pres-
ence of either a stable or radioactive isotope              Biological value (BV)             A measure of
and is therefore intrinsically labelled with the            protein quality. The term has a strict definition,
nutrient. The concentration of the intrinsic                but is also used more loosely as a synonym for
label in both diet and faeces can be used to                protein quality. BV is calculated by measuring
calculate the true digestibility of the nutrient            the faecal and urinary nitrogen losses of two
tested. In the presence of another isotope of               groups of growing rats: one given a protein-
the same nutrient that has been previously                  free diet, the other a diet containing the test
injected into the bloodstream of the subject                protein at a concentration of 10%:
animal and allowed to reach equilibrium, one                    BV = 100 (Ni – (Nu – Nue) – (Nf – Nfe)) /
can calculate the endogenous loss of the nutri-                 (Ni – (Nf – Nfe))
ent via the intestine.                       (JSJr)         where, for the rats given the test diet, Ni is
See also: Availability; Nutrient bioavailability            the nitrogen intake, Nu is urinary nitrogen
                                                            excretion, Nf is faecal nitrogen excretion; and,
                                                            for the rats given the protein-free diet, Nue is
Key references
Halberg, L. (1981) Bioavailability of dietary iron in
                                                            urinary nitrogen excretion (endogenous uri-
    man. Annual Review of Nutrition 1, 123–147.             nary nitrogen), Nfe is faecal nitrogen excretion
Klieber, M. (1961) Nutritive food energy. In: The           (metabolic faecal nitrogen).
    Fire of Life. John Wiley & Sons, New York,                  Thus, endogenous urinary nitrogen and
    pp. 253–265.                                            metabolic faecal nitrogen are added to the
Littell, R.C., Lewis, A.J. and Henry, P.R. (1995)           nitrogen retained to give the total amount of
    Statistical evaluation of bioavailability assays. In:   nitrogen utilized. This is divided by the nitro-
    Ammerman, C., Baker, D. and Lewis, A. (eds)
                                                            gen truly absorbed (i.e. faecal nitrogen is cor-
    Bioavailability of Nutrients for Animals:
                                                            rected for endogenous loss) to give the
    Amino Acids, Minerals and Vitamins. Acade-
    mic Press, San Diego, California, pp. 5–33.             biological value, which is therefore indepen-
Small, B.C., Austic, R.E. and Soares, J.H. (1999)           dent of digestibility. BV is related to the sim-
    Amino acid availability of four practical feed          pler measure, net protein utilization (NPU):
    ingredients fed to striped bass Morone saxatilis.           BV = NPU true digestibility.
                                               Black gram                                         53




   Although originally designed and strictly         Birth weight          The weight of an animal
defined as a test with rats, it has also been         at the moment it is born. Within species, this
adapted for use with other animals.    (MFF)         weight will depend on the breed of the ani-
See also: Protein quality                            mal’s parents and the genetic material that it
                                                     inherits from them. The uterine environment
Biotechnology           A technology that uses       also has a significant effect on birth weight. If
biological systems and processes to produce          an embryo is transferred from one female to a
substances of medical, biological, nutritional       smaller one, the birth weight of the resulting
and other commercial significance. It includes        newborn is likely to be lower than if it had
use of cell and tissue culture, cell fusion, mole-   been carried to term by its own dam. Manipu-
cular biology, and recombinant deoxyribonu-          lation of ova and embryos prior to transplant-
cleic acid (DNA) technology to generate              ing has been known to increase birth weights
unique organisms with new traits or organ-           by up to 50%, resulting in severe problems at
isms that have potential to produce specific          parturition. Fetal requirements for energy,
products. The most common applications               protein and minerals increase rapidly, espe-
include fermentation to produce antibiotics,         cially during the last third of gestation.
brewery products and cheese. Genetic engi-           Because of this, restricting energy intake to
neering allows the isolation of a desired gene       the mother can reduce birth weight; while
and its insertion into the DNA of another            increasing the energy intake of the ewe in the
organism which is then grown for the com-            last 6 weeks of pregnancy, for example, can
mercial production of insulin, hormones, vac-        increase the birth weight of lambs. Specific
cines etc. The same technology is used to            nutritional deficiencies can cause debility,
produce microorganisms that degrade haz-             deformation and death of the newborn, rather
ardous wastes, as well as genetically modified        than reduced birth weight per se. As litter size
plants and animals.                          (SPL)   increases, the birth weight of each individual
                                                     in the litter tends to decrease. Early parturi-
Biotin         C10H16N2O3S, one of the water         tion results in lower birth weights. Newborn
soluble B-vitamins. It is the vitamin co-factor      animals of lower than average birth weight
for pyruvate carboxylase, which forms                are more likely to die.                 (PJHB)
oxaloacetate, and for acetyl-CoA carboxylase,
                                                     Biuret          Biuret is the common name for
which is the first step in fatty acid biosynthe-
                                                     imidodicarbonic diamide or carbamylurea,
sis. It is also the co-factor for propionyl-CoA
carboxylase which is involved in the conver-         NH2·CO·NH·CO·NH2. It reacts with an aque-
sion of propionate to succinate, which can be        ous solution of copper sulphate and sodium
a source of glucose carbon. In addition it is a      hydroxide to give a purple-coloured complex.
co-factor in the carboxylase step of leucine         Proteins and some amines react in a similar
catabolism. It is normally synthesized in ade-       manner to biuret, thus forming the basis of
quate quantities by the intestinal bacteria. It      the colorimetric method for the quantitative
occurs normally in a variety of foods.               determination of proteins. The method is sim-
                                                     ple, robust and reliable but lacks selectivity
                              H
                                                     since all proteins react in a similar manner.
                                   N                                                           (JEM)
                       S                   O
                                   N                 Black gram           An annual dicotyledonous
                                                     plant (Vigna mungo), native to central Asia,
                              H                      grown for forage, silage and hay. It is an
                                                     important feed for livestock in India, with
                                                     dietary inclusion rates of up to 17% (Saran et
                                                     al., 2000). It is also grown in chicken pas-
     O                                               tures. Fodder is derived mainly from the stem
              O                                      and leaves but the seeds, pods and pod husks
                                            (NJB)    are also used. Black gram is usually fed to
54                                          Blindness




cattle as a fodder but it may also be consumed     Bloat        Bloat is most commonly observed
by other species, including chickens. The          in ruminants, as a disorder of rumen function
silage of black gram in the dough stage has a      that causes swelling or tympanites of the
dry matter (DM) content of 273 g kg 1, with        rumen. It sometimes occurs in pigs, when the
crude protein (CP) at 139 and crude fibre (CF)      small intestine becomes colonized by gas-pro-
at 191 g kg–1 DM. The pods of the black gram       ducing bacteria. In cattle it can be observed as
plant have much lower levels of CP at 90 and       an acute swelling between the last rib and the
CF at 299 g kg–1 DM. Black gram seeds have         hip on the left side. The animals are restless,
a CP level of 261–268 and a very low CF level      find lying uncomfortable and may eventually
of 53–56 g kg–1 DM. The pod husks have a           die of heart failure or of suffocation due to
CP level of 166 and CF 246 g kg–1 DM. (JKM)        inhaling rumen contents.
                                                       Bloat in ruminants is caused by consump-
                                                   tion of either large quantities of rapidly
Key references                                     digested carbohydrate (gassy, feedlot or cereal
Göhl, B. (1981) Tropical Feeds. FAO, Rome.
                                                   bloat) or pasture legumes (pasture or frothy
Saran, S., Singh, RA., Singh, R., Rani, S.I. and
   Singh, K.K. (2000) Feed resources for rearing
                                                   bloat), which create a stable foam in the
   livestock in the Bundelkhand region of Uttar    rumen. Gassy bloat is usually due to sudden
   Pradesh. Indian Journal of Animal Sciences      consumption of cereals, particularly if they
   70, 526–529.                                    have been excessively processed, which accel-
                                                   erates bacterial digestion. This may occur if
Blindness             Nutritional problems that    an animal loses its appetite for a period, and
cause blindness in animals generally do so by      then compensates by overeating. This type of
interfering with the function of the nervous       bloat can be treated by releasing the gas with
tissue comprising the visual centre of the cere-   a stomach tube or in an emergency by a
bral cortex, the optic nerve or the retina. Thi-   rumen trocar and cannula. Sometimes bloat
amine deficiency can result from inadequate         can be caused by an obstruction in the
dietary thiamine in non-ruminants or, in rumi-     oesophagus, such as a piece of food that is
nants, from the presence of thiaminases (e.g.      stuck. This can often be removed by passing a
from eating high-concentrate diets, bracken        stomach tube to release the gas.
fern or raw fish), which destroy thiamine               Pasture bloat is of more economic impor-
before it can be absorbed. Polioencephaloma-       tance as it can affect a large group of animals
lacia, or degeneration of the cerebral cortex,     at the same time. Lucerne is the most likely of
ensues, destroying vision. Sulphur toxicity can
                                                   all legumes to cause bloat, with cows some-
also induce polioencephalomalacia. Lead poi-
                                                   times dying within a few hours of entering a
soning, from ingestion of used crankcase oil
                                                   field for grazing, but it can also be caused by
and grease or discarded lead batteries, results
                                                   young leafy grass that has recently received
in loss of visual cortex function. Arsenical
                                                   nitrogen fertilizer. Some legumes contain tan-
compounds, once used as pig growth promot-
ers and to control swine dysentery, can, in        nins, which reduce the speed of protein diges-
large amounts, cause degeneration of the           tion and probably discourage animals from
optic nerve. Vitamin A deficiency causes reti-      grazing those plants. Tannins are present in
nal degeneration, leading to night blindness.      sufficient quantities in bird’s-foot trefoil to pre-
Eventually the optic nerve may become              vent the production of a stable foam, and their
involved and vision lost completely. Water         content in white clover increases sufficiently at
deprivation followed by rapid replenishment        flowering to make it safe to graze. If a mixed
of water (also known as sodium toxicosis) can      grass-and-clover sward has enough clover to
cause oedema of the brain tissues, blocking        cause bloat (probably more than 50% of the
vision. In the nervous form of ketosis, blood      herbage by mass), it should not be grazed for
glucose levels may fall to the point at which      long periods but should either be conserved, if
the function of the visual cortex is depressed,    there is sufficient mass, or rested for a few
resulting in partial blindness.           (JPG)    weeks until the clover inflorescences appear,
See also: Lead; Night blindness; Thiamine          after which it can be grazed or conserved.
                                                  Blood                                                55




    Cows are most likely to become bloated in          from the tissues to excretory organs. Blood
the late evening after a day’s grazing and also        also aids in the maintenance of pH, fluid and
after a wet period when they avidly graze to           electrolyte balance in the body, aids tempera-
make up for lost time. Wet grass reduces saliva        ture control and is important in defending the
production, and the saliva contains a mucin            body against pathogens.
that disperses foam in the rumen. Herbage                  Blood can be divided into a cellular compo-
that has been frozen is particularly likely to         nent and a fluid component. These can be
cause bloat, as the rupture of plant cell walls        separated by centrifugation. The cellular com-
releases a lot of potassium. Potassium-rich            ponent normally makes up 30–55% of blood
feeds, such as molasses, are notorious for             volume, depending on species. The fluid com-
causing bloat, whereas grasses rich in sodium          ponent, plasma, will coagulate on exposure to
appear to be less likely to cause it. The precise      air, to form serum and a fibrinogen clot. With
mechanism has not yet been determined but              platelets (thrombocytes), and by the action of
may relate to the stimulation of saliva produc-        the coagulation cascade, fibrinogen forms a
tion by sodium-rich feeds, and the foam-dis-           clot when blood vessels are damaged. This
persing properties of the salivary mucin.              can act as a self-defence mechanism to pre-
    Forage supplements will usually slow down          vent further blood loss.
the rate of digestion and reduce bloat but, if             Cells that are found in the blood fall into
there is adequate herbage, grazing supple-             three groups: red blood cells (erythrocytes),
ments may not be eaten by some cows in suffi-           white blood cells (leukocytes) and platelets
cient quantities, particularly if they are based       (thrombocytes). There are around 500–1000
on straw or other low quality forages. Mineral         times as many red blood cells as white. Ery-
oils also help to disperse the foam and can be         throcytes are biconcave disc-shaped cells mak-
added to a concentrate feed or sprayed on to           ing up around 32% of blood volume.
the pasture or the cows’ flanks, to be licked off       Mammalian erythrocytes have no nuclear
as needed. Linseed oil is often used. A propri-        material but those of birds, fish and reptiles
etary product, poloxalene, also breaks up the          do. They are formed from cells that originate
foam and can be used as a drench for clinical          principally in the bone marrow and survive in
cases or included in feed blocks as a preventive       circulation for 3–4 months. Structurally they
measure. Often simply walking the cow from             are envelopes containing haemoglobin, the
the field to the farmstead to receive medica-           iron-containing pigment that colours the
tion will alleviate the swelling. It is important to   blood and absorbs oxygen. Oxygen is trans-
keep a bloated cow on her feet if possible, as         ported from oxygen-rich areas, the lungs, to
death can follow soon after recumbency.                oxygen-deprived areas where O2 is exchanged
    There are reported breed differences in the        for CO2, which is then returned to the lungs.
susceptibility of cattle to bloat: Jersey cows             Leukocytes, which are larger than erythro-
are particularly prone to the disorder. Cows           cytes, are nucleated and are involved in body
can get used to feeds that are liable to make          defence. They are divided into two major
them bloat; this may be by altering their              groups: granulocytes, which originate from
behaviour to spread their meals out more               bone marrow precursors, and lymphocytes,
evenly over the day. Lactating cows are par-           which come from lymphatic tissues around
ticularly susceptible, due to their high intakes.      the body.
Pasture bloat remains a serious problem in                 Granulocytes include neutrophils (polymor-
countries like New Zealand, where the cattle           phonuclear leukocytes), which are phagocytic
rely on pasture with little or no fertilizer           cells that are present in circulating blood but
applied and a high legume content.          (CJCP)     also able to migrate from blood vessels into tis-
                                                       sues. Classically, numbers rise in response to
Blood         The fluid transport system of the         bacterial infection. Eosinophils, with red-staining
body, circulating within the cardiovascular sys-       granules, are also phagocytes but are associated
tem. It transports nutrients from the gut, oxy-        with parasitic infections and some allergic condi-
gen from lungs, hormones from endocrine                tions. Basophils contain histamine that is
glands to body tissues and waste products              secreted during allergic reactions. Monocytes
56                                           Blood flow




are phagocytic and migrate from blood vessels       See also: Anaemia; Haemoglobin; Immunity
to tissues, where they are called macrophages;
they tend to be involved in chronic infections.     Blood flow           The degree to which an
    Lymphocytes are present in circulating          organ or tissue, via its network of capillaries,
blood but are also found in lymphoid tissues,       is perfused by blood. Blood flow can be mea-
e.g. Peyers’ patches in the intestinal wall,        sured by the flow (as ml min 1) in the artery
spleen, tonsils and lymph nodes. They are           supplying it, or in the vein draining it, using
involved in specific immunity, either as B cells     various tracer dilution techniques, or by an
in the humeral response, e.g. antibody-secret-      ultrasonic or electromagnetic flow probe
ing cells (plasma cells), or as part of the cell-   implanted around the blood vessel.         (DS)
mediated immune system.
    Blood groups are recognized in animals          Blood meal           A deep red/brown granu-
and are used in thoroughbred identification.         lar powder obtained from blood collected at
Blood transfusions can be used, particularly to     slaughterhouses. It is processed by gentle
treat blood loss or shock, but usually only         heating until fully coagulated; the excess
once, due to the formation of antibodies to         water is drained off by pressing and finally
the ‘foreign’ blood group.                          the residue is dried and ground. It is occa-
    Some of the measurements made on blood          sionally further ground to form a very fine
include: (i) haematocrit or packed cell volume      powder known as blood flour, which is more
(PCV), which measures the proportion of             soluble although harder to handle. Blood
blood that is in cells; (ii) red, white and total   meal is a good food material that is readily
(TBC) blood cell counts; (iii) differential white   eaten by all animals, although it can be
blood cell counts, which determine the differ-      unpalatable at first. Modern drying methods
ent types of white blood cell present and can       apply heat gently, which allows blood meal to
give an indication of the morphology; (iv)          be produced with a minimum of heat dam-
haemoglobin levels – in total for the blood         age. The dry matter is almost pure protein,
and, in combination with red cell counts, for       with high concentrations of essential amino
individual red blood cells (MCH); and (v) blood     acids except isoleucine. Excessive heat sub-
chemistry, enzyme and hormone levels.               stantially reduces its digestibility but mild heat
    Disorders of the blood include anaemia          improves its value to ruminants by reducing
(lack of red blood cells), leukaemia (a malig-      solubility in the rumen.
nant disease of lymphoid tissue that is espe-           Under       The     Bovine        Spongiform
cially common in the cat, where, unlike in          Encephalopathy (No. 2) Order 1996 (SI
humans, there is rarely an increase in num-         1996 No. 31663) it was still permitted to
bers of leukocytes in the blood) and thrombo-       feed blood meal to both ruminant and non-
cytopaenia (lack of platelets – causes include      ruminant animals in the UK and Europe,
poisoning). Haemolytic disease of the new-          although this practice was not common. How-
born can result from an incompatibility             ever, following the Processed Animal Protein
between the blood of the sire and dam and is        Regulations 2001 of 1 August 2001, this
thought to be the cause of some late abor-          practice is no longer permitted in the EU for
tions in cattle. In foals, puppies and piglets,     animals kept, fattened or bred for the produc-
antibodies in colostrum cause haemolysis of         tion of food.
red cells; exchange transfusions have been
                                                    Typical analysis for blood meal.
performed to save severely affected foals.
Haemophilia is rare, but is seen in dogs and        Component (units)                           Weight
cats. Haemolysis is the destruction of red cells
with the release of haemoglobin; some infec-        Dry matter (g kg 1)                          900
                                                    Metabolizable energy (MJ kg 1 dry matter)     13.2
tions and poisons can cause this. Blood circu-
                                                    Crude protein (g kg 1 dry matter)            940
lation can carry pathogens or pathogenic            Ash (g kg 1 dry matter)                       10
substances round the body, leading to               Oil (ether extract) (g kg 1 dry matter)       10
pyaemia, septicaemia, viraemia or toxaemia.
                                             (EM)                                                  (MG)
                                        Body composition                                             57




Blood plasma             The fluid portion of       pared. For some purposes, the empty body,
unclotted blood consisting of 93% water and        that is liveweight minus gut contents, is an
5–7% protein with electrolytes, nutrients such     appropriate base line. After slaughter, the
as glucose, amino acids, lipids and some vita-     empty body minus the major internal organs
mins, hormones, metabolic waste products           may be regarded as the eviscerated body. If
and small amounts of gases. Albumin, fibrino-       the skin and hair are removed and an
gen and globulins are the three major pro-         allowance is made for the evaporative loss of
teins. Globulins (particularly IgG) are produced   cooling, then a ‘carcass weight’ is obtained.
by the humeral immune system in response to        Carcass weights may be reported with the
the stimulus of specific antigens and can be a      head on or off.
source of passive immunity.                 (EM)       The simplest chemical description of body
See also: Immunity                                 composition is in terms of proximate analysis
                                                   – dry matter (or water content), fat (lipid), pro-
Boar          An entire male pig (see also         tein (usually as N 6.25) and ash. With small
Pigs). In the growing phase, boars require         species, it is practicable to homogenize the
higher quality diets than castrates or gilts       entire body and take aliquots for analysis.
because of their higher protein deposition         More detailed analyses can reveal the status of
rate. They also have a lower appetite and thus     the reserves of macro- and micronutrients.
can usually be fed ad libitum to slaughter             Studies of tissue-related composition are
without incurring carcass grading penalties.       often undertaken to give a link between the
Their higher protein:fat ratio in liveweight       chemical composition and the economic value
gain makes them the most efficient type of          of the carcass. The major differences in body
pig in terms of feed utilization, and the pre-     composition amongst animals of the same
ferred option in countries where age at            species usually relates to the ratio of fat (lipid) to
slaughter is low enough to minimize the risk       fat-free (lipid-free) body, or that of ‘adipose tis-
of boar taint in the meat. When used as            sue depots’ to ‘lean tissues’. Elsley et al. (1964)
breeding animals, their feed requirements will     showed a remarkable stability between the ratio
depend on liveweight, housing temperature          of bone to muscle and in the ratios of lean parts
and mating frequency. Under practical farm         of the carcass to one another in sheep and pigs
conditions, boars are usually fed a restricted     that had been grown on profoundly different
amount of 3–4 kg day 1 of the same diet as         nutritional regimes. The composition of the fat-
the gestating sows, given in one or two daily      free component of the body appears relatively
meals. Both extreme overfeeding and under-         constant both within and across species. This
feeding can adversely affect libido, while pro-    applies whether the fat is defined as chemically
longed underfeeding can also reduce sperm          determined fat (lipid) or as dissectible fat. Blaxter
production. Adequate levels of calcium, phos-      (1989) gave percentage values for the concen-
phorus and biotin are essential for soundness      tration of water and protein in the fat-free (lipid-
of legs. Semen quality can be beneficially          free) body for a number of species. These were,
affected by dietary supplements of n-3 fatty       respectively, for hens, 71.9 and 22.1, for rab-
acids and by antioxidants such as vitamin E        bits 72.8 and 23.2, for sheep 71.1 and 21.9,
and selenium.                             (SAE)    for pigs 75.6 and 19.6, for oxen 71.4 and
                                                   22.1 and for the horse 73.0 and 20.5. The
Body composition           Body composition        close similarity suggests a powerful functional
can be defined either in chemical or tissue-        relationship across all species.
related terms. In an agricultural context, it is
not always easy to define what should be con-       Factors affecting the proportion of fat in the
sidered as ‘the body’ because there are a          body
number of major components of liveweight,          Fatty tissue is late maturing and is characteris-
such as the gastrointestinal tract, that are of    tically increased in mature animals. Young ani-
little value. The degree to which these are        mals prioritize lean growth and tend to be
included or excluded in an analysis can cause      vulnerable if food becomes scarce, because
confusion when different results are com-          they have small energy reserves. A feature of
58                                         Body condition




early selection for domestic animals was to         Key references
prize those that had a propensity to fatten         Blaxter, K.L. (1989) Energy Metabolism in Ani-
easily, because these had a greater survival            mals and Man. Cambridge University Press,
capability and in adverse times were a ready            Cambridge, UK.
                                                    Elsley, F.W.H., McDonald, I. and Fowler, V.R.
food source for starving humans. Modern
                                                        (1964) The effect of plane of nutrition on the
selection techniques have favoured leaner ani-
                                                        carcasses of pigs and lambs when variations in
mals to such an extent that some functionality          fat content are excluded. Animal Production 6,
has been lost. For example, in domestic pigs,           141–154.
sows have become so lean that they cannot
sustain a normal or extended lactation. Hill        Body condition          A simple, often largely
sheep too are disadvantaged if they are exces-      subjective assessment of the fat and muscle of
sively lean, since they lose some of the insu-      an animal, to judge its readiness for slaughter
lating value of subcutaneous fat when               or breeding. It may be expressed as a body
over-wintering and the ewes have difficulty          condition score.                          (MFF)
maintaining body condition if required to
suckle in the early spring.                         Body density: see Specific gravity
    Entire males are usually leaner than
females, which in turn are usually leaner than      Body fat         A term used to describe both
male castrates. The quest for carcass leanness      the amount of lipid in the body and the
has led to a reversal of castration policy in       amount of adipose tissue, which consists of
some countries and male pigs are left entire in     a matrix of connective tissue, blood vessels
several countries. Bulls too are left uncastrated   and specialized cells (adipocytes) in which lipid
in some production systems for the same rea-        is stored, mainly as triglycerides. The adipose
son, though this can bring management diffi-         tissue is subdivided into the subcutaneous,
culties because of their unpredictable              abdominal, intermuscular and intramuscular
aggressiveness.                                     depots. Subcutaneous fat is not uniformly dis-
    Nutrition can greatly affect the ratio of       tributed and in some species may be concen-
fatty tissues to lean body mass. Fat propor-        trated in specialized depots such as the hump
tions are greatly increased in growing pigs         or tail. The main abdominal fat stores are the
and poultry when the diet is deficient in pro-       omental and perirenal depots. Fat pads also
tein or in critical amino acids. Generous           surround other organs. Inter- and intramuscu-
feeding on high-energy diets can have the           lar fat are important to the cooking and eating
same effect, whilst restricted feeding usually      qualities of meat.                        (MFF)
produces a leaner carcass but slower growth
rates.                                              Body fluids          A general term embracing
    Although changes in nutrition have little       both intracellular and extracellular water and
effect on the composition of lean tissues, the      including blood, urine, saliva, sweat and other
fatty acid composition of the adipose tissue        secretions, water in the digesta and water
of non-ruminant animals can be profoundly           associated with tissues. The term is particu-
altered by the nature of the dietary fats.          larly used with reference to the maintenance
Diets rich in polyunsaturated fatty acids such      of normal hydration and osmotic balance.
as n-6 linoleic or linolenic acids can transfer                                            (KJMcC)
high concentrations of these fatty acids to
the depot triglycerides. The very long-chain        Body temperature: see Temperature, body
n-3 fatty acids of fish oils (eicosapentaenoic
and docosahexaenoic) can also be incorpo-           Body water          Body water includes all
rated in the triglycerides of the adipose           water contained in the body fluids and body
depots of pigs and poultry. Some nutrition-         tissues of the animal, though the term is
ists believe that this could confer a nutritional   sometimes taken to exclude water in the ali-
advantage to the animal fat as a component          mentary tract. Total body water can be esti-
of human diets.                            (VRF)    mated in living animals by dilution techniques
                                          Bone formation                                           59




(usually using labelled water, 2H2O or 3H2O).      Bone density          The amount of mineral
Body water content can be measured after           per unit of bone volume. The classical method
slaughter by desiccating samples of the            for measurement of bone density is based on
homogenized carcass. The water content of          Archimedes’ principle, requiring weights of
animals varies inversely with their fat content,   the bone in air and in water. Anatomical fea-
generally decreasing with age. The water con-      tures of bone such as the medullary cavity,
tent of the fat-free body is more constant but     trabecular spaces and the Haversian system
also decreases somewhat with age.                  create inaccuracies in measurements. Clinical
                                       (MMacL)     techniques such as dual-energy X-ray absorp-
                                                   tiometry (DXA) are used to estimate bone
Bomb calorimeter             An instrument for     mineral density, but these measurements are
measuring the heat of combustion (i.e. the         based on area (cm2) not volume (cm3). Esti-
gross energy) of a small sample of com-            mates of bone density by DXA are highly cor-
bustible material (e.g. food, body tissue, fae-    related with ash density, but bone mineral
ces). The bomb itself is an airtight stainless     density estimates are only weakly associated
steel container inside which the pre-weighed       with fracture incidence in humans.      (TDC)
sample (usually compressed into a small pellet)
is placed so that it is in contact with a firing    Bone diseases               Nutritionally related
device. Oxygen is admitted at high pressure        bone diseases fall into one of three categories:
through a valve and the bomb is then placed        those affecting the growth plate; failure to
in the calorimeter vessel, which is a copper       remodel mature bone properly; and diseases
                                                   characterized by retention of cartilage plugs
can containing water. This entire system is
                                                   within bone.
then placed on an insulated stand inside an
                                                       Rickets is the failure to mineralize endo-
outer vessel whose walls form a temperature-
                                                   chondral cartilage of growth plates; it is usu-
controlled water jacket. The temperature of
                                                   ally caused by vitamin D or phosphorus
the calorimeter and bomb is allowed to equili-
                                                   deficiency in young animals. Calcium defi-
brate with that of the water jacket and the
                                                   ciency may also induce rickets. Manganese
bomb is then ‘fired’ by means of a brief elec-
                                                   and copper deficiency reduce elongation of
tric pulse. The sample is completely oxidized
                                                   growth-plate cartilage by reducing proteogly-
in its oxygen-rich environment and the heat
                                                   can and collagen synthesis.
from its combustion causes a proportional rise
                                                       Bone is continuously undergoing resorption
in the temperature of the system comprising
                                                   and replacement by new bone in a process
the bomb, calorimeter vessel and water. An         called remodelling. Osteoporosis, primarily the
automatic control system is used to cause an       result of calcium deficiency, occurs when bone
equal rise in the temperature of the water         is resorbed but is not replaced by new bone.
jacket, which ensures that there is no heat        Since bone is a major depot of calcium this
loss from the calorimeter system; its tempera-     serves as a means of maintaining calcium
ture rise is thus a measure of the heat of com-    homeostasis. Osteodystrophy and osteomalacia
bustion of the sample. It is necessary to          occur when bone is resorbed and is replaced by
calibrate the device by means of test firing        bone matrix but not by bone mineral and are
with samples of a substance of known heat of       typically associated with vitamin D or phospho-
combustion. The whole procedure takes about        rus deficiency. In osteochondrosis (mammals)
30 min for completion and can yield esti-          and tibial dyschondroplasia (birds), areas of phy-
mates of heat of combustion accurate to            seal or epiphyseal cartilage fail to mineralize and
0.5%.                                  (JAMcL)     remain as weak points within the bones. This is
                                                   associated with diets (and genetics) that encour-
Further reading                                    age very high rates of growth.                (JPG)
McLean, J.A. and Tobin, G. (1987) Indirect         See also: Rickets
  calorimeters. In: Animal and Human Calorime-
  try. Cambridge University Press, Cambridge,      Bone       formation        Bone      formation
  UK, pp. 24–30.                                   involves a coordinated series of steps including
60                                            Bone meal




synthesis, secretion, posttranslational modifica-     to receptors on osteoblast cells, which release
tions, and repair (maintenance) of a complex         a localized factor to stimulate osteoclastic
extracellular matrix which can become mineral-       activity and hence increased bone resorption.
ized with hydroxyapatite-like crystals. Pre-         These signalling arrangements function to
osteoblast cells proliferate and differentiate as    couple bone formation and resorption for
they become embedded in an extracellular             modelling and remodelling of bone.       (TDC)
matrix. The embedded, fully differentiated
osteoblasts are called osteocytes. Signals direct-   Bone meal            Bone meal and products
ing the extent and location of new bone forma-       made from bone are most commonly used as
tion are mediated by osteoblasts, but formation      sources of phosphorus. Phosphates of rock
is coupled with removal of pre-existing calcified     origin (rock phosphate or lime phosphate)
hyaline cartilage in growth plates (endochon-        may, unless thoroughly treated, contain dan-
dral ossification), or stimulation of systemic hor-   gerously high levels of fluorine, whereas those
mones and growth factors that modulate               from bone are completely safe. Bone meal for
osteoblast proliferation (bone modelling, by         use as a phosphorus supplement is produced
endochondral and intramembranous ossifica-            by heating, drying and finely grinding fresh,
tion), or removal of existing mineralized bone       defatted bones from warm-blooded land ani-
by osteoclasts (bone remodelling). Additional        mals. This extracts most of the protein and
signals may originate with embedded osteo-           fat to leave monohydrogen phosphate
cytes that direct localized responses to mechan-     (CaHPO4·xH2O), also known as monocalcium
ical loads or fracture healing responses.            phosphate. This process is now tightly con-
    The bone extracellular matrix is composed        trolled within the EU under The Processed
of 40% collagen (primarily type 1 collagen) and      Animal Protein Regulations 2001 of
10–15% non-collagen proteins, which include          1 August 2001 and now includes treatment
proteoglycans (85% chondroitin sulphate,             with dilute hydrochloric acid (4%) over a
7–12% core protein and 5–7% keratan sul-             period of at least 2 days, after which the resul-
phate), glycosylated proteins and gamma-car-         tant liquor is treated with lime to form a pre-
boxylated proteins. The helical structure of         cipitate of dicalcium phosphate. Because of
collagen (see Collagen) provides tensile             these new regulations the most common
strength and, upon mineralization by growth of       sources of phosphorus now used in animal
hydroxyapatite-like crystals within the helix,       feed within the EU are from de-fluorinated
compressive strength. Proteoglycans (also            natural phosphates and composed of equal
called ground substance) are complex branched        parts of monocalcium and dicalcium phos-
polymers with negatively charged side-chains         phate (CaHPO4-Ca(H2PO4)2·H2O).              (MG)
that maintain the hydration state of the matrix.
    Mineralization follows secretion of the          Bone resorption: see Bone formation
extracellular matrix with initiation and
growth of hydroxyapatite-like crystals               Boron          A non-metallic element (B) with
(3Ca3(PO4)2·Ca(OH)2). The mineralized matrix         an atomic mass of 10.811. It does not occur
functions in both structural and storage             free in nature but combines readily with oxy-
roles. Deposition and resorption of mineral          gen to form boric acid, B(OH)3, and borate
responds to changes in mechanical loads              salts, B(OH)4 . Boron also forms esters with
and to systemic signals involved in calcium          oxygen-containing compounds, or will link
and phosphate homeostasis.                           with four oxygen atoms in adjacent hydroxyl
    Two systemic hormones, parathyroid hor-          groups to form identifiable biological com-
mone and 1,25 dihydroxyvitamin D3, are               pounds. Some of these B-containing com-
involved in bone formation through their             pounds can be isolated from nature, including
direct action on osteoblast metabolism.              boromycin, an antibiotic produced by certain
Osteoblasts also mediate systemic signals that       bacteria. Certain plant species have an
are transmitted through local signalling path-       absolute requirement for B, and recent experi-
ways to osteoclasts. For example, agents that        mental results suggest that B serves a physio-
increase bone resorption, such as PTH, bind          logical function in animals as well.
                                         Botanical composition                                      61




   Chicks raised on diets marginally deficient         of tall inflorescence-bearing stems. Vegetative
in vitamin D and without B showed more                development is arrested at this stage but, if
anomalies in bone maturation than chicks fed          conditions are right, a second flowering
marginal vitamin D and adequate B (3 mg               occurs in late summer. This is followed by a
kg 1). However, B would not substitute wholly         reduction in tillers during the winter. In the
for vitamin D. Additional dietary B (5 mg             semi-arid tropics lack of grazing material,
kg 1), compared with no B, enhanced body              often caused by drought, is the major limita-
weight gain in broilers.                              tion to grazing. For herbivores, leaves and
   Recent studies also have shown that B              young stems are the major source of nutri-
deprivation is detrimental to normal develop-         ents, with conservation of forage and supple-
ment of the embryos of the South African              mentary feed gaining in importance as their
clawed frog (Xenopus laevis), the zebrafish            nutritive value, or availability, falls.
(Danio     rerio)     and    rainbow     trout            The nutritive value of a grass sward will
(Oncorhynchus mykiss). Dietary requirements           depend not only on rainfall and fertilizer appli-
for farm animals have not been established.           cations but also on the frequency of defolia-
                                        (PGR)         tion, either by cutting or grazing. The more
                                                      often defoliation takes place, the greater is the
                                                      proportion of young leaves and shoots in the
Further reading
                                                      aerial part of the plant. Lignification of stems
Nielsen, F.H. (1997) Boron. In: O’Dell, B.L. and
   Sunde, R.A. (eds) Handbook of Nutritionally        will be minimized. Fewer defoliations, whilst
   Essential Mineral Elements. Marcel Dekker,         resulting in increased lignification, will lead to
   New York, pp. 453–464.                             an increased yield of dry matter.
Rossi, A.F., Miles, R.D., Damron, B.L. and Flunker,       Storage organs in food crops are generally
   L.K. (1993) Effects of dietary boron supplemen-    modified stems or roots, with non-lignified
   tation on broilers. Poultry Science 72,            secondary thickening. They are normally har-
   2124–2130.
                                                      vested and stored for use in the winter period.
                                                      For livestock, this group includes such crops
Botanical composition                Plants are
                                                      as fodder beet and mangels. Modern conser-
made up of a number of components, of
                                                      vation techniques and a consequent reduction
which the most important are meristematic
                                                      in the use of rotations has reduced the impor-
tissue, parenchyma and lignified tissue. The
                                                      tance of these crops as livestock feed but
first two are important as food material and
                                                      many are valued as vegetable crops.
are most plentiful in leaves, young stems, stor-
                                                          Seeds contain only small quantities of cel-
age organs and seeds. Lignified tissue has lit-
tle or no feeding value.                              lulose, making them edible by both humans
    Plants with upright stems and aerial buds         and animals. They usually contain very little
can only be grazed or cut once, whereas               water and, if kept dry, they remain dormant,
those that tiller can usually be defoliated sev-      allowing long-term storage. The most impor-
eral times during the growing season.                 tant crops in this group are the cereals and
Whereas annuals only produce tillers above            oilseeds. Seeds are valuable sources of starch,
ground (stolons), perennials can also produce         protein and fats (oils). Many of the crops
underground tillers, or rhizomes. In temperate        grown for their seeds for human consump-
climates the growing season lasts as long as          tion also contribute valuable by-products for
ambient temperatures are sufficient to main-           livestock feeding (e.g. oilseed cakes; bran and
tain growth. However, first flowering is con-           other miller’s offals; straws and stovers).
trolled by a combination of the amount of                                                          (TS)
vegetative growth and increasing day length.
The grazing season, as distinct from the grow-        Further reading
ing season, is dependent on rainfall being            Gill, N.T. and Vear, K.C. (1958) Agricultural
insufficient to cause damage through treading.             Botany. Camelot Press, London.
In spring, tillers develop rapidly and, if there is   Hopkins, A. (2000) Grass: Its Production and Uti-
no defoliation, this is followed by the growth            lization. Blackwell Science, Oxford.
62                                            Botulism




Botulism          Intoxication caused by toxins          mals. CAB International, Wallingford, UK,
elaborated by Clostridium botulinum, a                   pp. 325–339.
Gram-positive, spore-forming anaerobic bac-
terium which inhabits soils, litter, feed and the   Bracken fern (Pteridium aquilinum)
digestive tract. There are seven types of C.        A perennial rhizome-forming herb found in
botulinum, producing specific toxins: A, B,          many parts of the world. Its fronds are palat-
C, D, E, F and G. Types A, B and E are most         able to livestock but contain several toxins
important in humans, type C in most animal          that cause disease syndromes. The toxins
species and D in cattle. The incidence of botu-     include a thiaminase, ptaquiloside, an uniden-
lism is highest in birds. Botulism causes pro-      tified bone marrow suppressant, and possibly
gressive motor paralysis, characterized by          a cyanogenic glycoside. Ptaquiloside is a car-
progressive weakness and paralysis, and death       cinogen that causes urinary tract neoplasms in
by respiratory or cardiac paralysis.         (PC)   cattle that have grazed bracken for several
                                                    weeks. This has been called enzootic haem-
Bovine       spongiform      encephalopathy         aturia, as affected cattle often bleed into the
(BSE)           A fatal degenerative disease of     urinary tract. Poisoned animals also develop
cattle, related to other transmissible spongi-      leucopaenia,       thrombocytopaenia        and
form encephalopathies such as ovine scrapie,        anaemia. Bracken fern poisoning in horses is
and Creutzfeldt-Jakob disease of humans.            primarily neurological, probably caused by thi-
Neurones in the brain are progressively             amine deficiency. Sheep are relatively resis-
destroyed, leading to apprehension, hyper-          tant to bracken poisoning but some develop
sensitivity, ataxia and coma of affected ani-       bright blindness due to degeneration of the
mals, usually after several years of incubation.    retinal neuroepithelium.                  (LFJ)
BSE can be transmitted to a wide variety of
mammals by feeding diseased tissues. As the         Brackish water           Water that is less salty
infective agent is not destroyed by cooking,        than sea water (34–35 g l 1). Brackish waters
there is concern to avoid human infection.          are usually found in those portions of estuar-
The disease in cattle reached epidemic pro-         ies where fresh and salt water mix. This mix-
portions in the UK in the early 1990s due to        ing zone is typically called the middle estuary;
the inclusion in compound feeds of meat and         it is bracketed by the lower estuary, which is
bone meal made from carcass offal that              characterized by oceanic influences and is
included infected material, and it has              essentially sea water, and the upper estuary,
occurred sporadically in other countries. It        where there is a tidal influence but no intru-
was controlled in the UK by banning the use         sion of sea water.                        (RHP)
of meat and bone meal in animal feed. Simi-
lar bans on the inclusion of meat products in
animal feeds, and regulations excluding older       Further reading
cattle, bovine offals and nervous tissue from       Fairbridge, R.W. (1980) The estuary: its definition
the human food chain, are now in force in               and geodynamic cycle. In: Olausson, E. and
many countries. Animal feeding practices                Cato, I. (eds) Chemistry and Biogeochemistry
have had to adjust to the loss of these valu-           of Estuaries. Wiley Interscience, New York, pp.
able but potentially dangerous feedstuffs.              1–35.
                                  (RFEA, AJFR)
See also: Blood meal; Bone meal; Meat               Bran         The collective name for the layers
products                                            of tissue (pericarp, testa and aleurone)
                                                    removed during the processing of cereal
                                                    grains (e.g. wheat bran during flour process-
Further reading
                                                    ing). An important by-product for animal feed-
Hunter, N. (2000) Transmissible spongiform
  encephalopathies. In: Axford, R.F.E., Bishop,     ing that is generally low in starch content and
  S.C., Nicholas, F.W. and Owen, J.B. (eds)         energy value.                              (ED)
  Breeding for Disease Resistance in Farm Ani-      See also: Cereals
                                                         Breadfruit                                           63




Branched-chain amino acids                  The                  kales, turnips, forage rape, radishes and
three indispensable amino acids L-leucine                        mustard. Oilseeds include rapeseed, also
(CH3)2·CH·CH2·CHN+H3·COO–, L-isoleucine                          known as canola (Brassica napus, Brassica
CH3·CH2·CH·(CH3)·CHN+H3·COO– and L-                              campestris) and mustard seed (Sinapis
valine (CH3)2·CH·CHN+H3·COO–. They are                           spp.). All of the brassica family contain glu-
closely related in structure and metabolism,                     cosinolates which degrade readily to thio-
sharing the same enzyme (the branched-chain                      cyanates, isothiocyanates, nitriles and their
keto acid dehydrogenase) in their catabolic                      alkyl, alkenyl and aryl residues. These can
pathway. This enzyme complex is found in                         cause adverse effects such as goitre in animals
both the liver and extrahepatic tissues. The                     and humans. Some of the forage materials,
three interact in metabolism, such that an                       such as kale, also contain S-methylcysteine
excess of leucine alters the utilization of the                  sulphoxide (40–60 g kg 1 dry matter) which
others: this is called an amino acid antago-                     degrades in the rumen to yield dimethyl
nism. In cases where only one keto acid of the                   sulphoxide and then dimethyldisulphide,
amino acid is used, it will adequately serve as                  which causes haemolytic anaemia. The glu-
a source of the amino acid.               (NJB)                  cosinolates and their aglycones smell and taste
                                                                 pungent, flavouring the meat, milk and eggs
Branched-chain fatty acids            Branched-                  of animals that consume them. The oils of
chain fatty acids are not widely distributed but                 rapeseed and mustard seeds can contain sub-
are found in rumen contents, where they are                      stantial proportions of erucic acid but new cul-
produced during the catabolism of branched-                      tivars have low concentrations of erucic acid
chain amino acids by rumen microorgan-                           (< 50 g kg 1 of the oil) and glucosinolates
isms. Isobutyric acid, (CH3)2·CH·COOH, is                        (< 10 mol g 1 seed).                       (TA)
derived from the catabolism of L-valine; and
isovaleric acid, (CH3)2·CH·CH2·COOH, is                          Bread: see Bakery products
derived from the catabolism of L-leucine. (NJB)
                                                                 Breadfruit           A round green seedless
Branched-chain        keto     acids        The                  fruit approximately 20 cm in diameter, pro-
transamination products of the branched-chain                    duced by the breadfruit tree, which grows up
amino acids leucine, isoleucine or valine. The                   to 20 m high and has large tough lobed
transamination partner may be one of the other                   leaves. The fruit is cooked and used by peo-
branched-chain keto acids or -ketoglutarate.                     ple in a similar manner to potatoes, and is a
The transamination product of leucine is -                       staple food in the Pacific islands. It is related
ketoisocaproate, (CH3)2·CH·CH2·CO·COO ;                          to jackfruit (Atrocarpus integrifolia). Bread-
that of isoleucine is -keto- -methylvalerate                     fruit can be fed to all classes of livestock but
CH3·CH2·CH·(CH3)·CO·COO ; while that                             is often used for pigs. Dried fruit is ground to
of       valine      is        -ketoisovalerate,                 make meal for storage. The meal has a pleas-
(CH3)2·CH·CO·COO .                        (NJB)                  ant odour and is a good source of energy.
                                                                 Breadfruit meal has low protein, fat and fibre
Brassicas     The brassica family includes                       contents but is very high in carbohydrates
cabbages, Brussels sprouts, cauliflowers,                         (see table).



Typical composition of breadfruit products (g kg   1   dry matter).

                               DM(%)         CP            CF         Ash        EE         NFE     Ca       P

Breadfruit, ripe                 29.8        5.7           4.9         6.8      1.0         81.6    0.12   0.15
Breadfruit meal                  84.9        3.2           5.5         3.1      0.9         87.3    0.08   0.16
Breadnut, fibre and skins         13.4        6.5          18.1        11.2      4.5         59.7
Breadnut, seeds and shells       31.4       11.1          14.3         4.0      6.0         64.6

CF, crude fibre; CP, crude protein; DM, dry matter; EE, ether extract; NFE, nitrogen-free extract.
64                                       Brewery by-products




    Breadfruit is seedless but another variety,      residues of maize and rice. Fresh brewers’
called the breadnut, contains seeds. Fruits of       grains have a low DM content (250 ± 31.3 g
the breadnut have a rough surface covered in         kg 1 fresh weight) and high protein and fibre
conical spines, unlike the smaller bumps on          contents (218 ± 34.2 and 618 ± 63.9 g kg 1
the surface of a breadfruit. Both the seeds and      DM, respectively). They are widely used in rumi-
pulp of the breadnut are edible. The breadnut        nant feeding as a forage or concentrate feed
fruit has higher protein, fat and fibre contents      replacer or for buffer feeding and have an esti-
than the breadfruit, particularly so in the case     mated energy (ME) value of 11.5 ± 0.65 MJ
of the seeds.                               (LR)     kg 1 DM. They can be fed in their fresh state or
                                                     following ensilage or drying.               (ED)

Reference                                            Further reading
Gohl, B. (1981) Tropical Feeds. FAO Animal Pro-      MAFF (1990) UK Tables of Nutritive Value and
  duction and Health Series, No. 12. FAO, Rome.        Chemical Composition of Feedingstuffs. Rowett
                                                       Research Services, Aberdeen, UK, 420 pp.
Brewery by-products              Malt culms and      Moss, A.R. and Givens, D.I. (1994) The chemical
brewers’ grains are the main by-products of            composition, digestibility, metabolisable energy
brewing malted or unmalted cereal grains, par-         content and nitrogen degradability of some pro-
ticularly barley, and other starch-rich products.      tein concentrates. Animal Feed Science and
Other by-products include spent hops, waste            Technology 47, 335–351.
beer and brewers’ yeast, the latter usually
being incorporated with other by-products            Broiler chickens          Domestic fowl (Gal-
such as brewers’ grains. The by-products of          lus gallus) that are produced specifically for
brewing malted barley are shown in the figure.        meat production. The term ‘broiler’ originally
    Malt culms, also called malt sprouts, com-       referred to a size of bird that was suitable for
prise the dried radicle (rootlets) and plumule       rapid oven cooking (as opposed to roasting
(sprouts) of the germinated barley grains and        and frying) but now refers to all strains and
generally represent approximately 5% of the
                                                     sizes of chicken that are reared only for their
weight of malted barley. They are a good
                                                     meat. Broiler chicken strains were first pro-
source of protein (290 ± 56.9 g kg 1 dry mat-
                                                     duced around 1950 by crossing White Cornish
ter, DM), with a high fibre (556 ± 50.7 g neu-
tral-detergent fibre kg 1 DM) content and an          (also known as Indian Game) with Plymouth
estimated energy (ME) value of 11.1 ±                White Rock breeds. However, specialist poul-
0.95 MJ kg 1 DM. Because of their high fibre          try breeding companies now hold and select
content, they are generally fed only to rumi-        their own pedigree lines of birds that are pri-
nants and then, because of their bitter taste,       marily used in their selection programmes to
only at low levels. Wet brewers’ grains, also        produce commercially available broiler chick-
called draff, are the spent grains and the insolu-   ens. The efficiency of poultry meat production
ble fraction, including protein, following the       is improved if the broiler chickens are fast
removal of the wort, and may also contain            growing and deposit mostly lean tissue, rather

                  Barley
                         Malting               Malt culms (malt sprouts and hulls)
                  Barley malt
                         Mashing and filtration                 Brewers’ grains
                  Wort
                         Fermentation                 Brewers’ yeast
                            yeast                                Spent hops
                            hops
                  Beer
By-products of brewing malted barley.
                                             Broiler chickens                                         65




Day-old chicks require a temperature of 32°C, decreasing to 22°C at 20 days of age.


than fat, in their body growth. Continued              needs to be given to the birds during this time:
selection and development of broiler strains           either the whole rearing area is heated to the
has given birds that grow very fast, compared          required temperature or a number of small
with other strains and breeds of chicken, and          localized areas of heat are provided, using
tend to be slaughtered at weights that are less        heaters with a high radiant heat output. Day-
than half of their mature body weight.                 old chicks require a temperature of 32°C and
    Poultry breeding companies produce two             this requirement decreases by about 0.5°C per
lines of birds that provide either the females         day until they reach 20 days of age. Thereafter
or the males. The two lines are housed                 the broiler chickens are able to withstand a
together to produce fertile hatching eggs,             range of temperatures, although the most effi-
which are then transported to machine incu-            cient conversion of food inputs into bird growth
bators for a 21-day incubation period. The             occurs at a house temperature of 18–24°C.
hatched chicks, each weighing about 45 g,              For this reason, many broiler chickens are pro-
are taken to a rearing farm, where they are            duced in controlled environment houses in
grown to their slaughter weight. Slaughter             which a combination of good insulation, to
weights can vary from 1 to 3 kg, depending             retain the body heat emitted from the birds,
upon market requirements, but most broiler             and powered ventilation, to bring in cooler out-
chickens are slaughtered at about 2 kg.                side air, is used to maintain a desired optimum
    Most broiler production systems use solid          temperature. Other systems of partial environ-
floors covered with a thin layer of absorbent lit-      mental control and outdoor production may
ter material, such as wood shavings or straw.          also be used but these often incur higher pro-
Rearing in cages is possible for birds that are to     duction costs. Controlled environment housing
be slaughtered around 1 kg, but not suitable for       must have precise control of ventilation rates to
heavier weights of broilers. Floor-rearing sites       remove toxic gases (carbon monoxide, ammo-
may rear large numbers (tens of thousands) of          nia, etc.) and water vapour from the house.
birds in one flock and individual birds are             This type of building allows for control of light:
allowed to move around freely within the rear-         long day lengths with relatively dim light are
ing house. Day-old chicks have only a thin layer       frequently used in commercial broiler produc-
of down covering their body and have not               tion systems. Systems of cooling incoming air
enough feather growth to enable them to con-           can also be used in controlled environment
trol their body temperature adequately until           houses that are operated in climates with high
they are about 20 days of age. Additional heat         ambient temperatures.
66                                         Brouwer formula




    Broiler chickens are allowed ad libitum          34 days having eaten 3.1 kg of feed, and a
access to feed and water during their rearing        female bird should reach 2 kg in approxi-
period. Containers need to be distributed fre-       mately 38 days having eaten 3.4 kg of feed.
quently and evenly around the flock because                                                   (SPR)
many birds are not prepared to walk long dis-        See also: Chick; Chicken
tances to the feeders and drinkers. Feed is
moved mechanically within the house within           Key references
pipes that supply and fill small pans or in           Hunton, P (1990) Industrial breeding and selection.
open tracks that slowly move feed around the            In: Crawford, R.D. (ed.) Poultry Breeding and
house and give feeding access to the birds              Genetics. Elsevier, Amsterdam.
                                                     Sainsbury, D. (1992) Poultry Health and Manage-
throughout their length. Pipes are used to
                                                        ment, 3rd edn. Blackwell Scientific Publications,
convey water to hanging drinkers that allow
                                                        London.
up to 20 birds to drink at once or to small cup
or nipple drinkers designed for single bird use.
                                                     Brouwer formula             A formula for calcu-
    Broiler chickens remain in the rearing unit
                                                     lating heat production, proposed by Profes-
until they reach their slaughter weight. They
                                                     sor E. Brouwer, and recommended for general
are then caught and transported to a slaughter
                                                     use in 1965 by an international committee of
and carcass processing facility. One slaughter
                                                     scientists. As first published the equation
and processing site may receive birds from
                                                     relates heat production (M, kcal) to oxygen
many rearing sites. The transport of live
                                                     consumption (O2, litres), carbon dioxide pro-
chickens is relatively expensive and so the
                                                     duction (CO2, litres), methane production
broiler rearing farms are often clustered in
                                                     (CH4, litres) and urinary nitrogen (N, grams):
fairly close proximity to the slaughterhouse.
                                                         M = 3.666          O2 + 1.200        CO2
    Compound feed mills supply a number of
                                                         0.518 CH4 1.431 N
the broiler rearing units. A single feed is usu-
                                                         In SI units the equation is:
ally supplied at any one time, though the nutri-
                                                         M (kJ) = 16.18        O2 + 5.02      CO2
ent composition of the feed is changed as the
                                                         2.17 CH4 5.99 N
chickens grow. Broiler feeds are almost invari-          The equation has become widely accepted
ably based on cereals or other high-starch           for those farm animals that excrete urinary
feeds, but a variety of other feedstuffs may be      nitrogen in the form of urea (i.e. most of
included to meet the birds’ requirements for         them). Slight variations on the formula are
amino acids, fatty acids, minerals and vitamins.     more appropriate for use with poultry (based
The feeds are mostly pelleted. In general,           on uric acid) and fish (based on ammonia).
intakes of pelleted feed are higher than for                                                 (JAMcL)
mash feed and feed efficiency is improved.            See also: Indirect calorimetry
This also provides an opportunity to heat-treat
the feed, thus reducing contamination by
potentially harmful bacteria such as Salmo-          Further reading
nella. Typically a broiler chicken starter feed      Brouwer, E. (1965) Report of the Sub-committee
contains around 12.8 MJ metabolizable                   on Constants and Factors. In: Blaxter, K.L. (ed.)
energy (ME) kg 1 and 230 g protein kg 1,                Energy Metabolism. Proceedings of the 3rd
whereas a broiler finisher feed contains around          Symposium.     Academic      Press,     London,
                                                        pp. 441–443.
13.2 MJ ME kg 1 and 190 g protein kg–1.
    Poultry breeding companies are continually
improving the growth potential of their com-         Brown adipose tissue (BAT)              A spe-
mercial broiler stocks, so it is difficult to define   cialized adipose tissue found most promi-
the characteristics of broiler growth. Commer-       nently in some newborn vertebrates. Brown
cial flocks also vary in their growth perfor-         fat has mitochondria that can become uncou-
mance due to a variety of management,                pled so that the protons produced from sub-
health and dietary variables that occur              strate catabolism, which are normally used for
between flocks. However, a male broiler               ATP production, are released and the energy
chicken should reach 2 kg in approximately           that is normally utilized for the conversion of
                                               Buffer                                              67




ADP to ATP is lost as heat. This specialized        and the finger-like villi, the brush border
fat participates in non-shivering thermogen-        increases the absorptive surface about 600-
esis and because it is highly vascularized the      fold. A number of specific hydrolytic enzymes,
heat produced is distributed to the body via        including peptidases (aminopeptidases, dipep-
the blood.                               (NJB)      tidase and tripeptidase) located in the brush
                                                    border and carbohydrases (maltase, isomal-
Browning          Browning, known as non-           tase, sucrase, lactase, trehalase) attached to
enzymatic browning, carbonyl-amine brown-           the brush border, complete the degradation of
ing or the Maillard reaction, occurs when a         proteins and carbohydrates into amino acids
reducing sugar is heated in an aqueous              and monosaccharides, respectively. Entero-
medium with amino acids or proteins. The            kinase, which initiates the activation of pan-
reaction involves a condensation between the        creatic enzymes in the duodenum, is also
aldehyde group of a reducing sugar and a free       secreted from the brush border.           (SB)
amino group of an amino acid. In free amino
                                                    Buckwheat             Buckwheat       (Fagopyrum
acids or proteins, the -amino group of lysine
                                                    esculentum) is not a cereal but the seeds
is involved. The result is a decrease in the
                                                    have similar nutritional characteristics to
digestion and absorption of dietary lysine.
                                                    cereal grains. Buckwheat, also called saracen
                                          (NJB)
                                                    corn, has triangular seeds with a fibrous hull
See also: Maillard reaction                         (~ 20% of seed weight) surrounding a kernel,
                                                    which is generally used for flour manufacture.
Key reference                                       By-products of buckwheat include buckwheat
Lawrie, R.A. (1970) Proteins as Human Food.         hulls and buckwheat middlings but only the
   Butterworths, London.                            latter are generally suitable for feeding. Straw
                                                    is also produced following seed harvest.
Browsing         Eating of leaves and twigs             Buckwheat may be grown as a green forage
from trees and bushes. Most livestock species       crop. It is high in carbohydrates with, typically,
prefer either to browse or to graze, though         549 and 129 g starch and crude fibre kg 1 dry
                                                    matter (DM), respectively. The protein content
many (including cattle and goats) are adapt-
                                                    is low (131 g kg 1 DM) and both the seed and
able. In semi-arid rangelands, leaves and fine
                                                    by-products tend to be deficient in calcium. The
stems are usually available into the dry sea-
                                                    grains are used for animal feeding and are
son, with the new season growth starting just
                                                    processed by grinding before feeding to most
before the onset of the rains. Browse plants
                                                    classes of livestock except poultry, to which they
often contain phenolic compounds.         (TS)
                                                    are fed whole. Their low palatability means they
                                                    are generally mixed with other cereals before
Brunner’s glands          Small glands in the       feeding. Buckwheat middlings have a high feed
duodenum that produce an alkaline secre-            value and are rich in protein (~ 300 g kg 1 DM)
tion of sodium bicarbonate (NaHCO3) that            and are generally used as part of the diet of
enters the duodenum through ducts located           dairy cows. The hulls are generally used only as
between the villi. The secreted bicarbonate,        fuel, bedding or packaging.                   (ED)
together with that from pancreatic secretions,
neutralizes the hydrochloric acid in the digesta    Further reading
that enter the duodenum from the stomach.           Centraal Veevoederbureau (1991) Veevoedertabel.
The glands are lacking in birds.            (SB)       CVB, Runderweg 6, Lelystad, The Netherlands.

Brush border           The brush-like surface       Buffalo: see Water buffalo
structure, formed by numerous microvilli, on
the membrane of the villi (the finger-like pro-      Buffer       A molecule that controls pH,
jections of the gut epithelium). The structure      modulating the concentration of protons (H+)
of the brush border substantially increases the     in solution by either releasing or taking up
absorptive surface area of the small intestine.     protons. Buffers can be inorganic (e.g. car-
Together with valve-like folds of the intestines,   bonic acid, H2CO3) or organic (e.g. acetic
68                                                Bulk




acid, CH3·COOH) molecules that participate              its probable metabolizable energy concentra-
in acid/base reactions, giving off or taking up         tion, because the starch-containing endo-
protons. Buffers vary in the pH they are able           sperm in a grain has a higher density than
to maintain and their capacity to control pH.           the fibrous seed hull. However, there are
To work as a buffer the parent molecule must            many confounding factors and bulk density
partially dissociate and come into equilibrium          seems to be poorly related to energy concen-
with its components, i.e. CH3·COOH                      tration or nutritive value. Terms used to
CH3·COO– + H+. It is the capacity of acetic             describe bulk density are bushel weight or
acid in solution to dissociate into an acetate          specific weight (kg per hectolitre). The latter
anion and a proton that makes it a buffer.              is used in international trading of cereals. For
                                          (NJB)         example, the accepted minimum for feed
                                                        wheat is 72 kg hl 1 and for bread-making
Bulk        Approximately 25% of a typical              wheat is 76 kg hl 1.                      (SPR)
poultry feed consists of components that cannot
be digested by chickens. Certain ingredients            Bull        The mature male of any species of
may be added to increase the indigestible com-          Bovini (cattle) and of certain other species.
ponents and increase the bulk density of the            The term is usually applied after the animal
feed and these are described as bulking agents          has reached sexual maturity. The primary
or feed diluents. Examples of these materials           function of the bull is to produce spermatozoa
are sand or clay, ground straw or sawdust, or           and introduce them into the female reproduc-
cereal grain hulls such as wheat or oat bran.           tive tract at oestrus in order to fertilize any
   Birds respond to an increase in the bulk             ova (sing. ovum, q.v.) that are shed some
density of their diet by increasing their volun-        hours after the end of oestrus. The bull’s
tary feed intakes and so there is no change             reproductive tract consists of primary, sec-
in their nutrient intakes. However, the figure           ondary and accessory sex organs
shows that this compensation may not be                     The primary sex organs consist of a pair of
exact.                                     (SPR)        testes, which are suspended in the scrotum
                                                        between the hindlegs. The testes contain sem-
Key reference                                           iniferous tubules, which produce the sperma-
Leeson, S. and Summers, J.D. (1997) Commercial          tozoa, and cells that produce testosterone,
   Poultry Nutrition, 2nd edn. University Books,        which gives the bull its libido. The secondary
   Guelph, Ontario.                                     sex organs are made up of the epididymis,
                                                        where spermatozoa are stored and matured,
Bulk density         The bulk density of an             and the duct system, including the penis,
individual sample of a feed such as a cereal is         which transport the semen to the cow’s
widely used in the feed trade as a measure of           vagina at mating. The accessory sex organs


                   Gut fill limits    Bulk density within range           A need for a
                   the increase       where food intakes are              minimum of gut fill
                   in food intake     altered to maintain a               increases nutrient
                                      constant nutrient intake            intakes


                                     Feed intakes
         Intakes




                                     (g bird–1 day–1)




                                        Nutrient intake


                                         Increasing nutrient density
                                           Decreasing bulk density
                                                     Butterfat                                           69




comprise the seminal vesicles, prostate and                acid and -hydroxy butyrate; longer-chain fatty
Cowper’s (bulbo-urethral) glands, which add                acids are absorbed from the bloodstream for
buffers, nutrients, hormones and osmo-regula-              direct incorporation into milk triglycerides. The
tors to the semen.                                         butterfat content of milk varies between species,
    After puberty, semen production is essen-              being typically 3.9% in cows, 4.5% in goats and
tially a continuous process, although it can be            7.4% in sheep. Milk from dairy cows is eco-
impaired by severe malnutrition, which proba-              nomically most important and butterfat content
bly explains why there may be seasonal fluctu-              of milk from these animals is affected by geno-
ations in semen production of bulls living in              type, stage of lactation and nutrition.
harsh environments.                                            Cattle of the Channel Islands breeds pro-
    The bull’s hormonal status means that it               duce milk with a higher butterfat content (5%)
grows faster than the cow, reaches a higher                than the more numerous Holstein or Friesian
mature weight and is more active, leading to               breeds (3.9%); there is generally an inverse
higher maintenance requirements.         (PJHB)            relationship between genetic merit for milk
                                                           yield and butterfat content of milk.
                                                               Immediately after calving, cows produce
Key reference                                              colostrum, which has a very high fat content
Peters, A.R. and Ball, P.J.H. (1995) Reproduction          (6.7%). The butterfat content of normal milk
   in Cattle, 2nd edn. Blackwell Science, London.          declines over the first month of lactation and
                                                           then increases steadily throughout the rest of
Butterfat      The lipid fraction of milk, from            lactation.
which butter is made. Butterfat is secreted in the             By far the greatest influence on butterfat
mammary gland as globules that are lighter than            content of milk comes from nutrition. Since
the whey fraction and therefore form a cream               acetic acid and -hydroxy butyrate are major
layer in whole milk. Butterfat consists of triglyc-        precursors for de novo synthesis of milk fat,
erides that are synthesized in the mammary                 dietary factors that influence the production of
gland from glycerol and a mixture of fatty acids           these acids in the rumen, such as digestible
ranging in chain length from 4 to 22. Shorter-             fibre intake, have direct effects on the butter-
chain fatty acids (up to 16 carbon atoms) are              fat content of milk. Intake of long-chain fatty
synthesized in the mammary gland from acetic               acids is positively related to their content in




                                                      Prostate   Rectum

                   Seminal vesicles

                         Ampullae
                            Bladder
                            Urethra                                               Cowper’s
                                                                                  glands
                     Vas deferens

                    Penis                                                          Retractor
                                                                                   muscles


                                      Testis
                                 Scrotum

                               Epididymis

The reproductive tract of the bull (lateral view).
70                                           Butyrate




milk, but if dietary fat content exceeds 60 g      Reference
kg 1 dry matter (DM), rumen digestion of           Bauman, D.E., Corl, B.A., Baumgard, L.H. and
fibre can be disrupted through the physical            Griinari, J.M. (2001) Conjugated linoleic acid
and detergent effects of long-chain fatty acids       (CLA) and the dairy cow. In: Garnsworthy, P.C.
                                                      and Wiseman, J. (eds) Recent Advances in Ani-
on fibre particles and rumen microorganisms,
                                                      mal Nutrition – 2001. Nottingham University
respectively. This problem can be overcome
                                                      Press, Nottingham, pp. 221–250.
by feeding the fatty acids in a protected form
as calcium salts, as small particles with a high   Butyrate        A four-carbon saturated fatty
melting point, or encapsulated in formalde-        acid, CH3·CH2·CH2·COO–. It is produced in
hyde-treated casein.                               the fermentation of feedstuffs in the rumen
    Since the early 1980s, worldwide con-          and in the lower intestinal tract of both rumi-
sumption of butterfat has declined due to the      nant and non-ruminant animals. Together
perceived adverse effects of saturated fats on     with the other steam-volatile fatty acids,
cardiovascular disease; butterfat typically con-   acetate and propionate, it forms a major part
tains 60–70% saturated fatty acids. Increasing     of the energy supply of ruminants.        (NJB)
the proportion of unsaturated fatty acids in
milk is difficult because unsaturated fatty acids   Butyric acid: see Butyrate
are hydrogenated in the rumen, unless they
are fed in a protected form.                       By-product          A product of plant or ani-
    Studies have shown that conjugated             mal production that is incidental to the main
linoleic acid (CLA), found mainly in milk fat      product for which the plant or animal is
and ruminant meat, has powerful anticarcino-       intended. Plant by-products include those
genic properties. CLA also reduces the inci-       from the milling, brewing and distilling indus-
dence of atherosclerosis and diabetes, and         tries. Animal by-products include those from
repartitions energy away from body fat             meat, fish, butter and cheese production.
towards muscle tissue (Bauman et al., 2001).       Many feeds (e.g. oilseed meals), formerly con-
This fatty acid, therefore, has tremendous         sidered by-products, may be comparable in
potential for improving human health. CLA is       importance and value to the primary product.
produced in the rumen from incomplete bio-                                                    (MFF)
hydrogenation of linoleic acid and in the          See also: Bagasse; Blood meal; Bone meal;
mammary gland by the action of delta-9             Bran; Brewery by-products; Citrus products;
desaturase on vaccenic acid. The main factors      Dairy products; Distillers’ residues; Dried skim
that raise the CLA content of milk are grazing     milk; Feather meal; Fish products; Hatchery
fresh pasture and increased intake of linoleic     waste; Meat products; Milling by-products;
and linolenic acids.                      (PCG)    Poultry offal meal; Whey
                                            C

Cabbage         Cabbages (Brassica spp.) are     tion (bacterial) in experiments involving esti-
members of the brassica family commonly          mation of digestibility based on measurements
grown for human consumption but also used        of nutrient contents of excreta (faeces +
as fodder for ruminants. The crude protein       urine). The results of such studies have shown
content of cabbages ranges from about 150        variable changes in digestibility, which is
to 250 g kg 1 dry matter. The apparent           reduced for some nutrients. There is
metabolizable energy for ruminants is about      decreased uric acid excretion and improved
10–11 MJ kg 1 but is very low (< 1 MJ kg 1)      nitrogen utilization.                    (MMit)
for pigs. Cabbages contain glucosinolates        See also: Caecum; Digestibility
(about 20–30 mol g 1 dry matter). Sheep
fed cabbages perform well but tend to have       Caecum (or blind gut)             A blind sac of
elevated thyroid weights and increased inci-     the digestive tract located in the pig and rumi-
dence of Heinz bodies in their blood.   (TA)     nants at the ileocaecocolic junction of the
                                                 small intestine and colon. In birds, two caeca
Cadaverine                     A bacterial       are connected at this junction. In the horse
decarboxylation  product    of   L-lysine,       the caecum is connected to the small intestine
NH2·CH2·(CH2)3·CH2·NH2. It is found in           at the ileocaecal junction and is a large
decomposing animal protein.         (NJB)        comma-shaped structure mainly located on
                                                 the right side. The relative volume of the cae-
Cadmium           A mineral element (Cd) with    cum varies significantly between species,
an atomic mass of 112.411. It is found natu-     being much larger in herbivores than in omni-
rally in small amounts in rocks, soils and sea   vores. Carnivorous animals have a very small
water. There is no known metabolic function      caecum or (e.g. mink) none. The size (and
for Cd and it is generally considered toxic.     capacity) of the caecum in omnivores is influ-
Certain edible plants may accumulate Cd from     enced by diet. Prolonged feeding of diets rich
the soil. Although the amount accumulated        in fibre significantly increases both the size
may be small, animals or humans that con-        and volume of the caecum in the pig.
sume the plant material may obtain enough           Together with the colon, the caecum acts
Cd over time to cause kidney damage. Natural     as a site for the absorption of water and short-
antagonists to the intestinal absorption and     chain fatty acids produced in microbial fer-
organ accumulation of Cd are other dietary       mentation. In the rabbit, specific pellets are
minerals such as zinc, calcium, iron and cop-    produced in the caecum and recycled to the
per.                                     (PGR)   digestive tract after coprophagy, which allows
                                                 the utilization of vitamins and amino acids
Caecectomy          Surgical removal of the      produced by the microflora of the caecum.
caecum or, in birds, usually both caeca. Fol-                                                (SB)
lowing laparotomy under general anaesthesia,
the caecum is ligated at two points no more      Caeruloplasmin           A glycoprotein found
than 8 mm apart and as close to the ileocae-     in the 2-globulin fraction of mammalian
cal–colonic junction as possible. The caecum     plasma. It has a molecular mass of 150,000
is then excised between the two ligatures and    kDa and a maximum of eight atoms of cop-
removed. The procedure is generally per-         per per molecule. It is synthesized in the liver
formed in birds to eliminate caecal fermenta-    and is the major carrier protein for copper in

                                                                                              71
72                                            Caesium




blood, comprising more than 70% of plasma           Calcinosis         A degenerative condition of
copper. The concentration of caeruloplasmin         a tissue or organ marked by deposition of cal-
in plasma varies with the nutritional copper        cium salts in either an unorganized fashion, or
status of an animal or human. It also has fer-      as nodules or plaques, most frequently in
roxidase activity and is believed to function in    areas of tissue necrosis as seen in the degen-
iron metabolism by converting Fe2+ to Fe3+.         eration of skeletal or cardiac muscle related to
                                          (PGR)     vitamin E or selenium deficiency.            (DS)
See also: Copper
                                                    Calcitonin        A 32-amino-acid peptide
                                                    hormone secreted by the ‘c’ or parafollicular
Caesium         A highly alkaline metal (Cs)
                                                    cells of the thyroid gland in response to high
with an atomic mass of 132.9. It occurs in the
                                                    serum calcium concentration. It reduces
earth’s crust at about 1 ppm. There is no
                                                    serum calcium by blocking bone resorption.
known metabolic function for caesium. The
                                                                                          (HFDeL)
metal is normally associated with radioactive
fallout as 137Cs from nuclear explosions and        Calcitriol       A trivial name for the hor-
nuclear powerplant emissions. This radionu-         monal form of vitamin D3, 1α,25-dihydroxy
clide, which can accumulate in the tissues of       vitamin D3 (or 1,25-dihydroxy cholecalciferol).
plants, animals and humans, has a half-life of      It functions in intestine, bone and kidney to
more than 30 years.                     (PGR)       elevate serum calcium concentration through
                                                    a nuclear receptor mechanism.
Caffeine         1,3,7-Trimethylxanthine. It is
found in tea and coffee and their by-products.                                        HO
Caffeine stimulates lipolysis, which is activated
by epinephrine and norepinephrine through
adenylate cyclase by production of cAMP
from ATP. Increased cAMP activates hor-
mone-sensitive lipase and releases free fatty
acids from stored lipids. The inhibition by caf-              HO          HO
feine of phosphodiesterase, which breaks                                                     (HFDeL)
down cAMP, results in less degradation of
cAMP and maintenance of enhanced lipolysis          Calcium           A divalent metal with atomic
and free fatty acids.                       (NJB)   mass 40.08. In its ionic form it is required for
                                                    many functions in the plant and animal world.
Calbindin        A protein, belonging to the        It is most critically needed for nerve and mus-
superfamily of proteins containing a helix–         cle function, for constructing the skeleton, for
loop–helix, that binds calcium tightly.             cellular integrity and cell-to-cell adhesion, but
                                        (HFDeL)     is required in many other life processes.
                                                                                            (HFDeL)
Calciferol        A general term signifying a
compound possessing the ability to cure or          Calcium formate              The calcium salt of
prevent the disease rickets. Most often it          formic acid is an off-white crystalline powder
refers to either vitamin D2 or vitamin D3 (see      that is recognized as a preservative in EU leg-
figure).                                (HFDeL       islation. It is listed as ‘E238, Calcium formate,
                                                    C2H2O4Ca, suitable for use in all feeding
                                                    stuffs’. It is a neutral non-toxic substance, rela-
                                                    tively safe and pleasant to handle. In the gut it
                                                    reduces buffering capacity, selectively stimu-
                                                    lates beneficial bacteria and improves gut wall
                                                    health and absorptive efficiency, appearing
                                                    particularly beneficial to newly weaned piglets.
HO                      HO
                                                    Calcium formate may also be used as an aid
                                                    to making silage when its selective antimicro-
     Vitamin D3                Vitamin D2           bial properties are exploited.
                                                    Calf                                                 73




                O                  O                       some species and on plane of nutrition in all
                                                           species. Within a few hours of birth, the
      H    C            Ca               C    H            bovine calf can walk and see and all of the
                                                           adult organs are present, although the mam-
                O                  O                       mary glands of the female and the sexual
                                              (CRL)        organs in both sexes are not functional until
                                                           puberty. In the female, the ovaries are present
Calcium phosphate           Various salts of               and contain all the ova that will ever be pro-
calcium with phosphorus are used as mineral                duced. In the male, the testes will usually have
supplements for farm livestock. The main two               descended into the scrotal sac.
are dibasic calcium phosphate, CaHPO4 (usu-                    The newborn calf is almost entirely depen-
ally anhydrous though the dihydrate is also                dent on its mother’s milk, not only for nutri-
available), and monobasic calcium phosphate                tion but also for disease immunity, since the
monohydrate, Ca(H2PO4)2.H2O. Both the cal-                 bovine placenta does not permit the passage
cium and phosphorus from these compounds                   of maternal antibodies into the fetus. The
are readily available to animals. The choice               rumen of the newborn calf is not developed
depends upon the proportions of Ca and P                   and does not contain the microorganisms nec-
required. Pure anhydrous ‘dicalcium phos-                  essary for its function. A reflex induced by the
phate’ contains just over 29 g Ca and almost               action of suckling stimulates the oesophageal
23 g P 100 g 1 but in practice, depending on               groove in the rumen to form a tube that deliv-
the source and method of manufacture, the                  ers milk directly to the abomasum, where ren-
amounts are 25–27 g Ca and 17–20 g P.                      nin causes coagulation as a prelude to
Actual levels of calcium and phosphorus sup-               digestion. If milk or milk substitute is ingested
plied by ‘monocalcium phosphorus’ monohy-                  too fast, which is more likely under artificial
drate are 15–17.5 g Ca 100 g–1 and 22–23 g                 rearing conditions, milk can spill from the
P 100g 1.                              (CRL)               oesophageal groove into the rumen. In the
See also: Dicalcium phosphate                              absence of the rumen microflora of the adult,
                                                           harmful bacteria can feed on this and cause
Calf         The young of any species of Bovi-             severe digestive upsets.
dae (cattle) and of certain other species, such                The calf would naturally suckle its mother’s
as deer. The term is usually applied from birth            milk for the first few weeks of life, after which
until the onset of puberty. This will occur at             this is gradually replaced with solid food as the
around 1 year of age, depending on season in               rumen develops. Calves in intensive milk pro-




The newborn calf depends on its mother’s milk, not only for nutrition, but also for immunity.
74                                            Calorifie




duction systems are usually removed from                The heat of combustion, or gross energy, of
their mothers within the first 2 days after birth    a substance is the energy converted into heat
and are fed milk or an artificial substitute until   when it is completely oxidized (i.e. burned) to
they are weaned on to solid food and water          carbon dioxide and water. It is a unique prop-
alone after 4–8 weeks. It is common for             erty of the substance, which can be measured
straw, or other roughage feed, to be made           precisely by use of a laboratory instrument
available to calves from a very early age in        called a bomb calorimeter. Although actual
order to help to stimulate rumen development        heats of combustion (J g 1) vary considerably
and function, but calves under intensive man-       within each food category (carbohydrate, fat
agement would also receive concentrate feed.        and protein), the heats produced per litre of
In the wild, calves may continue to suckle          oxygen consumed and per litre of carbon diox-
their mothers for many months, whilst gradu-        ide produced are remarkably consistent within
ally increasing their intake of solid food, which   each of the three. This makes it possible to
consists almost entirely of grazed or browsed       estimate an animal’s rate of metabolic heat
material. The microorganisms needed for             production with high precision by measuring
rumen function are picked up from the envi-         the respiratory gaseous exchange of oxygen
ronment. The newborn calf is susceptible to         and carbon dioxide (indirect calorimetry). The
cold but has relatively high levels of brown fat,   table gives heats of combustion (kJ g 1) of
which produces heat for thermoregulation.           some carbohydrates, fats and proteins.
                                          (PJHB)
                                                    Carbohydrate
Calorie           The heat required to increase      Monosaccharides (e.g. glucose, fructose)   15.6
the temperature of 1 g of water from 14.5 to         Disaccharides (e.g. sucrose, lactose)      16.5
15.5°C. Kilocalorie (kcal) and megacalorie           Polysaccharides (e.g. starch, cellulose)   17.5
(Mcal) refer to 103 and 106 calories, respec-       Fats                                        34–40
                                                    Proteins                                    22–25
tively. Unfortunately, the use of the terms
Calorie (with an initial capital) and CALORIE
(both intended to mean kcal), which are to be           The food energy value of a substance is
found in older textbooks, is still widespread,      the metabolizable energy, or that part of
especially in food packaging. This practice is      the gross energy which is potentially useful to
confusing and strongly to be discouraged.           an animal and not discarded as the energy of
    The calorie is not part of the Standard         waste products (i.e. faeces, urine and com-
International (SI) system of units. The SI unit     bustible gases). Food tables express the
of energy is the joule, which is defined as the      metabolizable energy per unit weight of sub-
work done in moving a distance of 1 m               stances. These are not unique properties of
against a force of 1 newton (N). The relation-      the food substance but depend on the diges-
ship 1 cal = 4.184 J is known as the mechan-        tive processes of the animal. Different food
ical equivalent of heat; it emphasizes the fact     tables are appropriate for carnivores, herbi-
that heat, like work, is a form of energy. Even     vores and omnivores. Metabolizable energies
though technically out of date, the use of ‘cal’    of different food constituents are generally
and ‘kcal’ in the agriculture and food indus-       additive, allowing the overall value of a diet or
tries is still widespread. In this volume energy    ration to be assessed.                  (JAMcL)
values are quoted in both joules and calories
whenever needed to avoid confusion.                 Calorimeter:    see          Bomb     calorimeter,
                                        (JAMcL)     Calorimetry; Direct         calorimetry; Indirect
See also: Calorific factors; Energy units; Joule     calorimetry

Calorific       factors      Calorific    factors     Calorimetry        The measurement of heat.
express the energy per unit weight of a sub-        A calorimeter is the instrument used for its
stance. It is important to distinguish between      measurement. The bomb calorimeter, a
two types of calorific factors, namely heats of      laboratory bench instrument, is used to mea-
combustion and food energy values.                  sure the heats of chemical reactions, espe-
                                             Camelids                                                   75




cially the heats of combustion of foods and        milk in composition (see table). The milk is
individual food components. Animal calorime-       greatly prized by camel herders, who may rely
try is the measurement of the heats produced       on it for water and nourishment for many days
by and given off from living animals and it has    on end. The animals are often shorn for their
been used with animals ranging in size from        wool. The alpaca remains the chief provider of
mice to horses. Distinction must be made           wool in Peru while the vicuna has an excep-
between direct calorimetry, which is the           tionally fine and valuable coat. In Arabia the
physical measurement of heat given off by the      dromedary is bred and trained for racing,
animal, and indirect calorimetry, in which         showing remarkable endurance, and this calls
the measurements are of the chemical quanti-       for special diets (Allen et al., 1992).
ties involved in metabolism; the heat gener-       Composition of milk of the dromedary compared with
ated is calculated from the heats of               the dairy cow (g kg 1) (Narjisse, 1989).
combustion of the end products. Indirect
calorimetry thus measures heat production,                                                       Total
                                                            Protein Lactose    Fat      Ash     solids
whereas direct calorimetry measures heat loss
by the animal to its environment. In the long      Camel      40       42       43       8       134
term the two must agree, but over short peri-      Cow        38       49       44       7       138
ods there may be an imbalance between heat
production and heat loss with a consequent            There are some 17 million dromedaries
change in body temperature.           (JAMcL)      and bactrian camels in the world; India, China
See also: Heat balance                             and Ethiopia have about 1 million each. They
                                                   may live for up to 40 years. Puberty is
Further reading                                    reached at 2–5 years, depending on health
McLean, J.A. and Tobin, G. (1987) Animal and       and nutrition. The gestation period is from 12
  Human Calorimetry. Cambridge University          to 13 months and the interbirth interval 2 or
  Press, Cambridge, UK.                            3 years. The shorter-lived South American
                                                   camelids have an 11-month gestation period.
Camelids           The Camelidae (camels and       They can interbreed and produce fertile
llamas) belong to the suborder Tylopoda,           hybrids. Much research has been done on the
closely related to, but distinct from, the Rumi-   control and manipulation of reproduction and
nantia. Today there are only six species. The      embryo transfer (Allen et al., 1992).
two larger camels, the one-humped drome-              The dromedary is particularly well adapted
dary, Camelus dromedarius, and the two-            to dry savannah and scrubland pastures
humped bactrian camel, C. bactrianus,              (Rutagwenda et al., 1990). It takes forage
originated in Arabia and Iran–Turkestan,           from ground level to 3 m high and eats from a
respectively. The four smaller species, the        wide variety of plants. Its divided prehensile
llama, Lama glama, the alpaca, L. pacos, the       upper lip allows it to select green shoots from
guanaco, L. guanicoe, and the vicuna,              among thorny twigs and it also strips off leaves
Vicugna vicugna, came from South America.          by pulling twigs through its mouth. Its long
    Only the guanaco and vicuna remain wild,       legs and ability to travel without water for
although small feral populations of the other      some days give it a wide grazing radius around
species may be found. The llama and alpaca         a water supply. It has wide footpads, not sharp
have been domesticated for some 4000 years         hoofs, and so can walk easily over soft ground.
and the dromedary and bactrian camel for              The camel’s digestive system is functionally
3000 years (Clutton-Brock, 1981). They have        very similar to that of true ruminants, although
all served as general farm stock and as pack       anatomically distinct (Wilson, 1984). In place of
and draught animals in the arid lands to which     the ruminant’s upper dental pad, the camel has
they are so well adapted. So successful was the    two incisors and one canine tooth. Rumination
dromedary as a pack animal in the desert that      and the vigorous secretion of the parotid sali-
wheeled vehicles were seldom seen in North         vary glands resemble that of the ruminant. The
Africa until 200 years ago. They provide           forestomach is divided into three compart-
excellent meat and their milk resembles cow’s      ments, analogous to the rumen, reticulum and
76                                              Candida




omasum but covered in a mucous non-papil-             Farid, M.F.A. (1989) Water and minerals problems
lated epithelium. This is followed by an acid-            of the dromedary camel (an overview). In: Tis-
secreting fourth compartment resembling the               serand, J.L. (ed.) Séminaire sur la digestion, la
abomasum. The forestomach shows a strong                  nutrition et l’alimentation du dromadaire,
                                                          Ouagla, Algerie, February–March 1988.
repetitive contraction at intervals, differing from
                                                          Options mediterranéennes, Série A, No. 2.
the minute-by-minute contraction of the reticu-           CIHEAM, Paris, pp. 111–124.
lorumen. Despite these differences in structure       Narjisse, H. (1989) Nutrition et production laitière
and motility, the camels ferment their food               chez le dromadaire. In: Tisserand, J.L. (ed.)
microbially in the forestomach, and produce               Séminaire sur la digestion, la nutrition et l’ali-
and absorb volatile fatty acids as a result, in           mentation du dromadaire, Ouagla, Algerie,
much the same manner as ruminants. Fibrous                February–March 1988. Options mediter-
particles are selectively retained in compart-            ranéennes, Série A, No. 2. CIHEAM, Paris,
ments 1 and 2 for prolonged fermentation. A               pp. 163–168.
gutter-shaped structure running from the car-         Rutagwenda, T., Lechner-Doll, M., Schwartz, H.J.,
                                                          Schultka, W. and Engelhardt, W. van (1990)
diac orifice of the oesophagus to the entrance
                                                          Dietary preference and degradability of forage
to compartment 3, resembling the rumino-                  on a semi-arid thornbush savannah by indige-
reticular groove, allows milk sucked by the calf          nous ruminants, camels and donkeys. Animal
to bypass the rumen.                                      Feed Science and Technology 31, 179–192.
    The metabolism of water and salt by the           Tisserand, J.L. (ed.) (1989) Séminaire sur la diges-
dromedary has been thoroughly investigated                tion, la nutrition et l’alimentation du dro-
(see Farid, 1989, for summary). The animal                madaire, Ouagla, Algerie, February–March
shows many adaptations to hot, dry conditions             1988. Options mediterranéennes, Série A, No
and tolerates long periods of water deprivation.          2. CIHEAM, Paris.
Concentrated urine (up to 3 osmolar) and dry          Wilson, R.T. (1984) The Camel. Longman, London.
                                                      Wilson, R.T. (1989a) The nutritional requirements
faeces (up to 60% dry matter) reduce excretion
                                                          of camel. In: Tisserand, J.L. (ed.) Séminaire sur
of water; heat storage by diurnal fluctuation of           la digestion, la nutrition et l’alimentation du
body temperature (37–40°C) reduces the need               dromadaire, Ouagla, Algerie, February–March
for evaporative heat loss; a furry coat protects          1988. Options mediterranéennes, Série A, No.
against solar radiation; and appropriate behav-           2. CIHEAM, Paris, pp. 171–179.
iour reduces heat production by day. The camel        Wilson, R.T. (1989b) Ecophysiology of the Camel-
appears to have a higher requirement for salt             idae and Desert Ruminants. Springer-Verlag,
than sheep or cattle, 1% NaCl in drinking water           Berlin.
being beneficial but 2% has a deleterious effect.      Wilson, T. et al. (1990) The One-humped Camel.
    Much has been published on the manage-                An Analytical and Annotated Bibliography
                                                          (1980–1989). Technical paper series No. 3.
ment, feeding habits, nutrition and diseases of
                                                          The United Nations Sudano-Sahelian Office.
camels in books and in the proceedings of
international conferences (see reading list).         Candida           Candida albicans is a yeast-
The nutritional requirements of camels under          like fungus that is a normal inhabitant of the
various conditions (work, lactation, etc.) and        nasopharynx, digestive tract and external gen-
the composition of preferred camel browse             italia. Disruptions of mucosal integrity may
plants are conveniently summarized by Wilson          result in Candida infections, most commonly
(1989a).                                    (RNBK)    in birds. Infection of the oral mucosa is called
                                                      thrush. In poultry, lesions are most common
                                                      in the crop. Thrush is common after use of
References and further reading
Allen, W.R., Higgins, A.J., Mayhew, I.G., Snow,
                                                      therapeutic levels of antibiotics or unsanitary
    D.H. and Wade, J.F. (eds) (1992) Proceedings      drinking facilities.                       (PC)
    of the First International Camel Conference,
    Dubai, February 1992. R & W Publications,         Cannula         A tube introduced surgically into
    Newmarket, UK.                                    a duct or cavity of the body. A narrow cannula
Clutton-Brock, J. (1981) Domesticated Animals         is more commonly called a catheter. Cannula-
    from Early Times. Heinemann/British Museum        tion is performed in order to sample repeatedly
    (Natural History), London.                        body fluids such as digesta, blood or secretions
                                              Carbohydrates                                        77




or to introduce material into the body.                chain fatty acid, shorthand designation 10:0.
    Cannulas in the digestive tract may be sim-        It is found in coconut and palm kernel oils.
ple, by which only samples of digesta are                                                        (NJB)
obtained, or re-entrant, by which the entire
flow is collected from the proximal cannula,            Key reference
measured, sampled and returned via the distal          Babayan, V.K. (1987) Medium chain triglycerides
cannula. Because a simple T-cannula, although             and structured lipids. Lipids 22, 417–420.
less invasive than a re-entrant cannula, allows
only sampling with no estimate of total flow, it        Caproic acid                    Hexanoic acid,
requires the inclusion in the diet of an indi-         CH3·(CH2)4·COOH, a saturated medium-
gestible marker which follows the flow of the           chain fatty acid, shorthand designation 6:0. It
nutrient. A further problem, common to both            is found in coconut and palm kernel oils.
types, is that the cannula is relatively small and                                               (NJB)
may give unrepresentative samples, especially
with fibre-rich feeds. None the less, cannula-          Caprylic acid                   Octanoic acid,
tion at the terminal ileum is routinely used for       CH3·(CH2)6·COOH, a saturated medium-
determining the ileal digestibility of one or          chain fatty acid, shorthand designation 8:0. It
more nutrients, in particular amino acids. A
                                                       is found in coconut and palm kernel oils.
more advanced technique, the post-valvular T-
                                                                                                 (NJB)
cannula, has a large cannula placed in the cae-
cum opposite the ileocaecal valve. Using a
nylon cord it can be steered in such a way             Carbohydrates           The most abundant
that, during a collection, virtually all the digesta   group of organic compounds in the world.
passing through the ileocaecal valve is directed       There are three classes: monosaccharides,
into the cannula. Ileal digesta can be collected       oligosaccharides and polysaccharides. Plants
without cannulation by slaughtering animals            produce carbohydrates by photosynthesis for
and sampling digesta post mortem or by a sur-          their own needs, simultaneously providing a
gical modification such as ileostomy or ileorec-        stored form of solar energy. Higher animals
tal anastomosis. However, results indicate that        and microorganisms use carbohydrates as
the terminal ileum alters in its physiology and        energy sources and as precursors of more
microbiology to assume some of the roles of            complex compounds.
the large intestine.                                       The term carbohydrate was originally
    Cannulas (catheters) can be guided under           coined because these molecules were believed
X-ray into particular blood vessels via superfi-        to be hydrates of carbon, having the general
cial veins or arteries. Cannulation of the car-        formula Cn(H2O)n. Structural characteristics
diovascular system may be combined with                common to carbohydrates are: (i) the carbon
flow measurement in order to quantify the               skeleton is unbranched; (ii) all but one carbon
flow of a component of interest. Cannulation            bears a hydroxyl group; and (iii) one carbon
of secretory ducts, e.g. those of the salivary         exists as a carbonyl group which, if on a ter-
glands, pancreas or gall bladder, may be used          minal carbon, gives rise to an aldehyde but if
to follow changes during development and               on an internal (centrally placed) carbon, typi-
responses to feeding, diet composition, etc.           cally carbon 2, it creates a ketone. These
    Cannulation may influence the composi-              compounds are known as aldoses and
tion or flow of the fluid being sampled; thus            ketoses, respectively. Sugars of five or more
results need to be evaluated carefully.         (SB)   carbons in length have a strong propensity to
                                                       form a ring structure through the reaction of a
Canola: see Rape                                       hydroxyl group on one carbon with the alde-
                                                       hyde or ketone to produce an internal hemi-
Canthaxanthin: see Carotenoids                         acetal or hemiketal and thereby a furanose or
                                                       pyranose ring. In so doing, a new asymmetric
Capric acid                        Decanoic acid,      or chiral centre is generated. This carbon is
CH3·(CH2)8·COOH,         a   saturated medium-         known as the anomeric carbon and the
78                                             Carbohydrates




hydroxyl group generated may exist in an                sugars can be depicted in a variety of ways on
or configuration (Fig. 1).                               a plane surface. The International Union of
   The smallest molecules generally termed              Pure and Applied Chemistry and the Interna-
carbohydrates are glyceraldehyde and di-                tional Union of Biochemistry have recom-
hydroxyacetone, also the only possible three            mended carbohydrate nomenclature that
carbon sugars, or trioses. The most abundant            indicates structure, configuration and linkages,
naturally occurring carbohydrates are the five-          although many of the more common carbohy-
carbon (arabinose, xylose and ribose) and six-          drates have deeply entrenched trivial names.
carbon (glucose, fructose, mannose and                      Monosaccharides are commonly joined
galactose) monosaccharides (Fig. 2) and poly-           together through a glycosidic linkage to pro-
mers of these. Monosaccharides have the                 duce di-, tri-, oligo- and polysaccharides. This
general formula (CH2O)n.                                is formed between the anomeric carbon atom
                                                        of one monosaccharide and any hydroxyl
     CH2OH                         CH2OH                group on another monosaccharide through
             O                             O            formation of an acetal. A common linkage,
 H                H            H               OH
                                                        which produces a linear chain, is between car-
     H                             H
     OH      H                     OH      H            bon 1 of one monosaccharide and carbon 3
HO               OH           HO                H       of the adjacent monosaccharide, denoted as
                                                        (1→3); a branch on this linear chain may be
      H     OH                      H     OH            between carbon 1 of the branching monosac-
α-D-Glucopyranose             β-D-Glucopyranose         charide and carbon 6 of the monosaccharide
Fig. 1. Alpha and beta-D-glucose are anomers            in the chain, indicated as (1→6). Several
whose sole configurational difference resides in the     derived monosaccharides have very important
sterid arrangement about carbon atom 1; this ‘car-      metabolic functions. Reduction of the alde-
bonyl’ carbon is also called the anomeric carbon        hyde groups of an aldose gives a polyhydric
atom. The plane of the ring projecting from the plane   alcohol, or alditol. Sugars are phosphorylated
of the paper are the thicken edges. In the alpha con-   as the first step in animal metabolism. Amino
figuration, the hydroxyl goup on carbon atom 1 is        sugars have a hydroxyl group, usually on the
below the plane of the ring and is so projected on a    carbon 2 atom, replaced by an amino group.
flat surface. In the beta configuration, the hydroxyl
                                                        Replacing a hydroxyl with a hydrogen, usually
group on carbon atom 1 is above the plane of the
ring and is so projected on a flat surface.
                                                        on carbon 2 or 6, produces deoxy sugars.
                                                            The (1→4) and (1→6) links between glu-
                                                        coses, such as in starch, are hydrolysed in the
    Natural sugars are optically active (i.e.           small intestinal lumen of mammals by amy-
rotate the plane of polarized light) because            lases. Disaccharides from the diet, e.g.
they contain one or more asymmetric carbon              sucrose, lactose and maltose, as well as mal-
atoms, so that the number of stereoisomers              tose and isomaltose produced by the action of
can be considerable. Laevorotatory sugars are           amylase on starch, are hydrolysed to con-
indicated by a small capital L or a minus (–)           stituent monosaccharides by specific disaccha-
sign, and dextrorotatory sugars by a small              ridases in the mucosal brush border of the
capital D or plus (+) sign. Since the sign of           small intestine. Of the monosaccharide prod-
rotation of plane-polarized light provides no           ucts, glucose is actively absorbed, whereas
information about the configuration or the               galactose and fructose are absorbed from the
centres of asymmetry of the molecule, a con-            small intestine by facilitated diffusion.
vention of nomenclature has been devised to                 None of the -linked pentoses or hexoses
indicate configurational properties. This con-           are susceptible to the digestive enzymes of
sists of using D or L to indicate the centre of         animals, nor certain -linked polysaccharides
asymmetry most remote from the aldehydic                such as fructans, but they can be degraded by
end of the molecule. Further distinction is             microbial enzymes in the gut (see Fermenta-
required to identify the asymmetry of carbon            tion). Fermentation of these carbohydrates,
atom one, which is designated as or ori-                which are collectively known as dietary fibre,
entation. The linear and cyclic structures of           is an important source of energy for rumi-
                                             Carbon dioxide                                        79




                                            CH2OH                                 CH2OH
       CH2OH

                   O                  HO              O          H           H               O     H

                                              H                                     H
         OH                                   OH       H                           OH       HO
 HO                       OH          H                       OH            HO                     OH


                   OH                         H       OH                            H        H
           Glucose                            Galactose                              Mannose
    alpha-D-glucopyranose              alpha-D-galactopyranose                alpha-D-mannopyranose


                                              H


 HOH2C         O        CH2OH         H               O          H           H          O          OH

                                              H
                                                                             C                     C
          H        HO                         OH       H                           OH        H
  H                       OH          HO                      OH      HO    CH2                    H
                                                                                    C        C

         OH        H                          H       OH                            H       OH
           Fructose                              Xylose                              Arabinose
    alpha-D-fructofuranose                alpha-D-xylopyranose                alpha-L-arabinofuranose




 HOH2C         O             H


          H        H
  H                       OH


         OH        OH
             Ribose
      alpha-D-ribofuranose

Fig. 2. Most abundant naturally occurring monosaccharides in their most common structural forms.

nants and a minor source for non-ruminant            is an end-product of the catabolism of fatty
species.                               (JAM)         acids, carbohydrates and amino acids. In solu-
See also: Dietary fibre; Monosaccharides;             tion in the body carbon dioxide becomes car-
Oligosaccharides; Starch; Storage polysaccha-        bonic acid: this is rapidly converted
rides; Structural polysaccharides                    enzymatically to bicarbonate which is part of
                                                     the blood and tissue buffer system.
Carbon dioxide            A diatomic gas, CO2,          Metabolism can be likened to a slow burning
that makes up ~0.033% by volume of air. In           in which fuel (food) is combined with oxygen to
photosynthesis, plants use atmospheric CO2           provide the energy for life processes together
in the biosynthesis of all the organic compo-        with the release of carbon dioxide and waste
nents in their cells. In animals, carbon dioxide     energy in the form of heat. The amount of car-
80                                    Carbon-nitrogen balance




bon dioxide produced is similar though slightly        RE (kJ) = 51.83% C + 19.4% N
less than the amount of oxygen consumed,
                                                    where C and N (g) are retained masses of the
being approximately 0.35–0.47 l for every kilo-
                                                    elements. To use the technique it is necessary
joule (kJ) of energy converted into heat. The
                                                    to collect, weigh, sample and analyse all food,
table gives crude estimates of the carbon dioxide
                                                    faeces and urine over at least one 24 h
production (l day 1) of growing farm animals at
                                                    period, as well as measuring the quantities of
different body weights. For pregnant animals
                                                    carbon dioxide and methane expired.
these estimates should be multiplied by approxi-
                                                                                          (JAMcL)
mately 1.5, for laying hens by 1.75 and for lac-
                                                    See also: Indirect calorimetry; Respiration
tating animals by 2, or even 3 for a
                                                    chamber
high-yielding cow. For maintenance conditions
they should be reduced to about two-thirds.
                                                    Carboxylases         A group of enzymes
 Body weight   Chickens   Sheep    Pigs    Cattle   involved in incorporation of carbon dioxide
                                                    into metabolic intermediates involved specifi-
      50 g         2                                cally in gluconeogenesis (e.g. pyruvate car-
     100 g         4                                boxylase) and lipogenesis (e.g. acetyl-CoA
     200 g         7
                                                    carboxylase) and in the catabolism of leucine.
     500 g        10
       1 kg       16
                                                    In all these examples the vitamin biotin is
       2 kg       27        50                      involved as the enzyme co-factor.       (NJB)
       5 kg                 70      60
      10 kg                100     120              Carboxypeptidase           An exopeptidase,
      20 kg                180     220      200     hydrolysing peptide bonds from the C-terminus
      50 kg                300     400      400     of proteins. Carboxypeptidase A (carboxy-
     100 kg                        600      650     polypeptidase; peptidyl-L-amino acid hydro-
     200 kg                        800     1000     lase; EC 3.4.17.1) and carboxypeptidase B
     500 kg                                1600     (protaminase; peptidyl-L-lysine [L-arginine]
                                  (NJB, JAMcL)      hydrolase; EC 3.4.17.2) are secreted as inac-
                                                    tive procarboxypeptidases from the pancreas
Carbon–nitrogen balance             Apart from      and activated in the duodenum by trypsin. The
fat, which can represent 5–40% of the total         liberated products are free amino acids or di-
body mass of farmed animals, the remainder          or tripeptides. Carboxypeptidase A hydrolyses
or ‘fat-free body’ consists of 20–23% protein,      all linkages except those in which the terminal
70–75% water and small amounts of minerals          amino acid is arginine or lysine, whereas car-
and carbohydrate. Carbon and nitrogen bal-          boxypeptidase B only hydrolyses bonds with
ance is a technique for measuring energy            terminal arginine or lysine residues.      (SB)
retained in the body (as growth, milk, eggs         See also: Protein digestion
etc.) by assuming that all retained energy is in
the form of protein and fat. Energy retained        Carcass (or carcase)             Although the
as protein and as fat is the product of their       term may be used to describe a dead animal,
masses retained and their heats of combus-          particularly in the wild, in animal production
tion. Since protein is 52% carbon and 16%           systems it normally refers to animals that
nitrogen, whilst fat has 77% carbon and no          have been prepared for human consumption.
nitrogen, the quantities of retained protein        This usually implies the removal of the diges-
and fat can be calculated from the retained         tive tract and contents and sometimes other
carbon and nitrogen. These in turn may be           internal organs. However, the extent of
measured as the differences between the             preparation varies between animal species
quantities of the two elements in the food          and is also affected by religious and cultural
consumed and in the faeces and urine                restrictions. Poultry, for example, may be
excreted with allowance for the carbon lost in      sold intact, with feathers removed, eviscer-
carbon dioxide and methane during respira-          ated with head on, or (in most modern pro-
tion. The necessary calculations are encapsu-       cessing situations) plucked and eviscerated
lated in the equation for retained energy (RE):     with head and legs removed; however, parts
                                            Carotenoids                                            81




such as heart, liver, gizzard and neck may be       tial for the transport of long-chain fatty acids
returned to the eviscerated carcass (often in a     across the impermeable inner mitochondrial
separate plastic bag). Pigs are normally evis-      membrane.The role of carnitine palmitoyl-
cerated and shaved; the head may be                 transferase is to control the rate of mitochon-
removed or left attached. Cattle and sheep          drial fatty acid catabolism but medium-chain
are normally skinned and have the head and          fatty acids (up to C-8) are thought not to
lower parts of the legs removed. Depending          require carnitine for entry to the mitochon-
on consumer demand a variable amount of             drion and thus their rate of catabolism is not
subcutaneous and visceral fat may be                dependent on carnitine. The precursor of car-
removed. In Europe, as a result of bovine           nitine biosynthesis is trimethyllysine, produced
spongiform encephalopathy, it is now neces-         by methylation of protein-bound lysine by S-
sary to remove all spinal cord material to          adenosylmethionine.                        (NJB)
minimize the risk of contamination.
    As a consequence of these different prac-       Carnosine         A dipeptide, C9H14N4O3, of
tices, the proportion of ‘carcass weight’ to          -alanine and L-histidine ( -alanylhistidine). It
pre-slaughter weight varies. This ratio,            is found in both brain and skeletal muscle. The
described as ‘kill-out proportion’, is also         enzyme carnosine synthetase is widely distrib-
affected by the breed and stage of maturity of      uted in tissues. Tissue carnosine can be
the animal and by pre-slaughter feeding or          depleted in dietary histidine deficiency and this
fasting. There is also a difference between         complicates studies on histidine requirements.
‘hot carcass weight’, i.e. weight at time of
evisceration, and ‘cold carcass weight’, which      N
                                                                                 O
is the weight after a period of hanging in a                             N
refrigerated room. Typical kill-out proportions
are: broilers, 0.7–0.75; turkeys, 0.8–0.85;                      O                   O
cattle, 0.5–0.6; pigs, 0.75–0.8; sheep, 0.5.
                                       (KJMcC)              N
See also: Meat production; Meat yield
                                                                     N
Carcinogens             Substances that cause                                                   (NJB)
cancer. Most carcinogens in feeds are sec-
ondary carcinogens, requiring metabolic activa-     Carob         Carob seeds are a product of the
tion by hepatic cytochrome P450 enzymes.            leguminous Mediterranean tree Ceratonia sili-
Examples of carcinogens in feed include afla-        qua. The pods and seeds are sweet and palat-
toxin, fumonisins, pyrrolizidine alkaloids in       able. The fat content is ~ 5 g kg 1 and the
Senecio spp. and ptaquilosides in bracken fern      protein content 50–100 g kg 1. The apparent
(Pteridium aquilinum). The commonest                metabolizable energy for poultry is 5–6 MJ
dietary cause of cancer in livestock is bracken     kg 1 and 10–12 MJ kg 1 for ruminants.
fern, causing urinary tract cancer (enzootic        Although palatable due to the relatively high
haematuria) in cattle. This is a significant prob-   sugar content (about 200–300 g kg 1), the
lem in parts of Western Europe (especially          meal tends to contain tannic acid which
Britain), Asia, New Zealand and Central and         reduces nutrient digestibility and probably
South America. Bracken-induced tumours may          apparent metabolizable energy. Recommended
also occur in the nasopharynx, oesophagus           concentrations in poultry diets are less than
and forestomach of cattle. Infection with bovine    about 50 g kg 1 while adult ruminants may
papilloma virus type 4 is a predisposing factor.    accept levels as high as 100 g kg 1.      (TA)
Rainbow trout are especially sensitive to afla-
toxin-induced liver cancer, caused by dietary       Carotenes: see Carotenoids
levels of as low as 1 ppb aflatoxin.          (PC)
                                                    Carotenoids         A group of plant pig-
Carnitine                    Carnitine,             ments of which a small percentage give rise to
(CH3)3·N+·CH2·CH(OH)·CH2·COO–, is essen-            vitamin A activity and thus are called provita-
82                                          Carotenoids




Structure of all-trans β-carotene.

min A carotenoids. -Carotene (see figure) is         carotenoid absorption at higher intakes. With-
the most active provitamin A carotenoid.            out micelle formation, carotenoids are poorly
Provitamin A carotenoids such as , and              absorbed. Carotenoids are thought to be
carotenes are found in pasture grass, silage        absorbed by intestinal mucosal cells by a mecha-
and hay as well as in lucerne and green and         nism involving passive diffusion. Once inside the
yellow vegetables such as carrot and sweet          intestinal enterocyte, the carotenoid may be
potato. Cryptoxanthin and           -zeacarotene,   converted to vitamin A or absorbed as such.
which contribute provitamin A activity, are         There is variability in the ability of animals to
also found in yellow maize. The common              absorb carotenoid unchanged into the body. For
potato and white maize and other grains are         example, birds convert carotenes into vitamin A
virtually devoid of provitamin A activity.          with only trace amounts of carotenoid passing
Although a number of carotenoids can serve          unchanged into the tissues. Most species do not
as vitamin A precursors, they are not all bioe-     absorb carotenoids intact. Sheep, goats, pigs
quivalent. For example, -cryptoxanthin and          and rabbits contain virtually colourless body fat.
  -zeacarotene are reported to be 50–60%            In contrast, -carotene can be found in the
and 20–40% as biopotent as is -carotene,            body fat of the cow, horse and human.
respectively. In addition, not all carotenoid-          More is known about the metabolism of all-
like structures have provitamin A activity. For     trans -carotene than of any other carotenoid.
example, xanthophylls found in green leaves         Much of the conversion of -carotene is pre-
and lycopene found in tomatoes do not have          sumed to occur in the enterocyte of the small
provitamin A activity. The biopotency of            intestine through the action of a dioxygenase
provitamin A substances is also affected by a       which can cleave between the 15 and 15 car-
number of additional factors. The physical          bons yielding retinaldehyde as the primary
matrix in which the carotenoids exist within        product in a 1:2 ratio, respectively. Evidence
food plays a role in limiting their availability.   has also been provided for the eccentric or
Heating of plant foods prior to ingestion           non-central cleavage of -carotene yielding -
improves their bioavailability but may also         apo-carotenals which are then oxidized to -
lead to isomerization of the naturally occur-       apo-carotenoic acids and retinoic acid. The
ring all-trans configuration to cis configura-        extent of conversion of -carotene to vitamin
tions, which can reduce their biological value.     A is highly species dependent. The vitamin A
Appreciable amounts of carotene (and vitamin        activity (1 IU = 0.3 g all-trans retinol) avail-
A) may be degraded in the reticulum and             able from carotene is estimated at 1667 IU
rumen of grazing ruminants. In addition,            mg 1 in the chicken and at 400 IU mg 1 in
carotenoids are unstable to oxygen and light        horses and cattle. Swine may be even less effi-
exposure. Loss in green forages may occur           cient. High intakes of retinyl ester have been
during field curing (up to 80%), and hay             shown to reduce intestinal -carotene cleavage
stored for 2 years is estimated to contain less     activity, though the manner in which the con-
than 10% of the original carotenoid content.        version of -carotene to vitamin A is regulated
    The digestion of fat substances (including      is unclear. Retinaldehyde resulting from -
carotenoids) in non-ruminant animals takes          carotene cleavage is reduced to retinol fol-
place largely in the small intestine. Once          lowed by esterification with long-chain fatty
released from foods, carotenoids in bulk lipid      acids in the intestinal enterocyte. Retinyl esters
droplets in the intestine are acted on by bile      are the major lymphatic product of -carotene
salts and pancreatic lipase, forming mixed lipid    metabolism. Carotenoids (in a few species) and
micelles. The capacity of micelles to incorporate   retinyl esters are transported by chylomicrons
carotenoids may be one factor that limits           from the intestinal mucosa to the bloodstream
                                          Cashmere goats                                       83




via the lymphatics. Lipoprotein lipase acts on      nature. Temporary cartilage present in the
the chylomicron to release free fatty acids that    fetal skeleton is later replaced by bone but
are taken up by the liver and ultimately other      permanent cartilage remains unossified.
tissues.                                (MC-D)                                            (MMax)
See also: Vitamin A; Retinyl palmitate
                                                    Casein         A group of proteins found in
Carp: see Common carp; Grass carp                   milk, which precipitate under acid conditions
                                                    (pH < 4.6) to form a clot or curd. Casein con-
Carrageenan (Irish moss)             A polysac-     stitutes about 80% of the total proteins in
charide extracted from red algae in seaweed         cows’ milk and is the main ingredient of
(Rhodophyceae) used as a thickener and veg-         cheese. Casein is also precipitated by the
etable gum. It is composed mainly of potas-         action of rennin on milk, either in the ani-
sium, sodium, magnesium, calcium, sulphate          mal’s stomach or added during cheese manu-
esters and 3,6-anhydro-galactose copolymers.        facture; this curd is softer than that
Commercial carrageenan is frequently stan-          precipitated by acids.
dardized by dilution with sugars and mixed              The five major classes of casein found in
with salt to obtain food-grade gelling or thick-    milk are αs1-, αs2-, β, κ and , comprising 43,
ening agents.                             (JKM)     10, 31, 11 and 5% of total casein on aver-
                                                    age. Most casein is aggregated with calcium
Carrot           Carrots (Daucus carota) are        phosphate in large micelles ranging in diame-
widely distributed throughout the north tem-        ter from 30 to 300 nm; more than 90% of
perate zones. They are annual or biennial           the calcium in milk is associated with casein
herbs of which the larger-rooted late varieties     micelles. Spray-dried milk powder can be
are used for stock feed. Surplus supply and         reconstituted with water because the
reject carrots from the food industry are used      casein–calcium micelles retain their structure
to provide energy for livestock. Carrots con-       and redisperse.                          (PCG)
tain -carotene, vitamin A and phytochemi-
cals. Their high vitamin A content makes            Cashmere goats            Cashmere is one of
carrots a particularly valuable supplement for      the finest and most luxurious animal fibres and
hay and straw. Carrots can be fed to cattle,        is the undercoat of a number of breeds of
sheep and horses. They are low in protein but       goats selected over many years for the pro-
enhance forage intake levels. Prolonged use         duction of this highly valued fibre. The name
of carrots at high levels can produce a yellow      derives from Kashmir where, in former times,
colour in the milk fat of dairy cattle or carcass   the fibre was traded. Like all domesticated
fat of beef cattle. Typical inclusion rates are     goats (Capra hircus), cashmere goats are
10–15 kg day 1 for cows, 5 kg 100 kg 1              thought to be descended from the bezoar or
body weight for beef cattle and up to 5% of         Persian wild goat (Capra aegagrus). All are
the diet in ewes. Carrots are usually fed in        double-coated, carrying their fine cashmere
their fresh state but may be dried and ground       undercoat, produced by the secondary hair
into a meal for inclusion in compound supple-       follicles, beneath an outer coat of coarse
ments. The dry matter (DM) content of carrots       guard hair that grows from the primary folli-
is 110–130 g kg 1 and the nutritive composi-        cles. Both fibre types are found all over the
tion (g kg 1 DM) is crude protein 92–95,            body, except on the face and legs; the term
crude fibre 110, ether extract 15–17, ash            ‘undercoat’ is frequently misinterpreted as
70–75 and neutral detergent fibre 200–210,           meaning that the cashmere fibres are found
with ME 11.9–12.8 MJ kg 1 DM.              (JKM)    only on the undersurface or belly of the goat.
                                                    The main populations of cashmere goats are
Cartilage        A type of non-vascular sup-        found in China and Mongolia and through the
porting connective tissue composed of chon-         southern parts of Russia to Afghanistan and
drocytes and collagen fibres embedded in a           Iran. In recent decades small populations of
firm chondrin matrix. Cartilage is elastic,          cashmere goats have been established in the
translucent, bluish white and gelatinous in         USA, Australasia and in Europe, the last
84                                            Cassava




being based on a new synthetic breed, the           in the tropics and subtropics for its tuberous
Scottish cashmere goat.                             starch-filled roots. The mature cassava plant (12
    Cashmere goats are generally small: adult       months old) contains 6% leaves, 44% stem and
females (does) weigh some 40–50 kg and the          50% tubers. By-products of root processing are
males (bucks) about 60–70 kg. The fibre char-        8% peel and 17% pomace. The tubers contain
acteristics of the many breeds of cashmere          a glycoside, linamarin, concentrated in the skin
goat have been reviewed by Millar (1986).           which is hydrolysed by linamarinase, an enzyme
Cashmere mean fibre diameters are in the             also present in the plant, to release hydrocyanic
range 13–18.5 microns ( m). Coarser mean            acid (HCN). Bruising the roots activates the
diameters are not regarded by the textile indus-    enzyme. The HCN can be removed by heating,
try as conforming to the generally accepted         soaking or prolonged sun drying. Bitter varieties
definition of cashmere. Within a fleece having        contain more than 0.02% HCN and require
a mean fibre diameter of, say, 15 m, individ-        thorough processing before feeding. Most com-
ual fibres may range in diameter from less than      mercial varieties are sweet, with < 0.01% HCN,
8 to about 28 m. The best quality cashmere          and can be used raw. Slicing, soaking and dry-
has a mean fibre diameter of 14–15 m; it is          ing removes much of the HCN, as does cook-
dull, with no lustre, and is highly crimped, i.e.   ing. Mortalities have been reported in animals
the fibres have a tight spiral form. Cashmere is     drinking water used for soaking cassava.
generally white, but grey, brown and fawn               Both fresh and dried cassava roots are fed
cashmere is also produced. In coloured goats        to ruminants. Dried cassava roots can be used
the cashmere fibres are lighter in colour than       as a replacement for grain as an energy source
the guard hair. The weight of cashmere pro-         in the rations of dairy cattle, fattening beef ani-
duced per goat varies widely from about 150 g       mals and lambs. Although an excellent source
or less in animals producing the finest cash-        of energy, cassava is deficient in protein, fat,
mere, to around 400 g or more in those with         trace elements and vitamins. Cassava protein
coarser fibre. Cashmere fibres are the goat’s         is particularly low in the sulphur-containing
protection against cold winters and they grow       amino acids (lysine, methionine and cysteine).
seasonally. It is generally believed that growth    The inclusion of supplementary sulphur in the
is initiated by the shortening day length follow-   ration, along with a source of degradable pro-
ing the summer solstice and that it ceases at       tein or non-protein nitrogen, allows rumen
the winter solstice. There is evidence, how-        microbes to manufacture the necessary bal-
ever, that in some breeds the period of cash-       ance of amino acids. This also assists in the
mere growth is longer than 6 months. The            detoxification of HCN in the rumen and liver.
cashmere fibres are shed or moulted in the           Replacement of maize, oats or barley by cas-
spring, at which time the cashmere is generally     sava in dairy rations has no effect on milk yield
harvested by combing the goats.                     and can reduce production costs.
    Cashmere goats are seasonally poly-                 Grain in poultry rations can be partly
oestrus. Does come into heat at 21-day inter-       replaced by cassava chips or root meal, with
vals during the breeding season which, in the       supplementary methionine (0.2–0.3%) for lay-
northern hemisphere, extends from about             ers. Up to 20% inclusion in poultry rations
August to February. Gestation length averages       allows satisfactory production levels. Cassava
about 150 days.                           (AJFR)    tubers, with a digestible dry matter (DDM) of
                                                    92%, can replace up to 75% of cereal in pig
Reference                                           rations, provided that the final ration contains
Millar, P. (1986) The performance of cashmere       no more than 100 ppm HCN, producing
    goats. Animal Breeding Abstracts 54(3),
                                                    leaner carcasses than grain-based diets. As with
    181–199.
                                                    poultry rations, attention must be paid to bal-
Cassava (Manihot esculenta Crantz)                  ancing the energy:protein ratio in the ration.
Also known as manioc, tapioca, Brazilian                Cassava leaves can also be used as feed,
arrowroot and yuca, cassava is a herbaceous         especially to provide undegradable protein
shrub up to 4 m high with fingerlike leaves. It      (UDP) to ruminants. Unlike the roots, the
can develop into a small tree. It is widely grown   leaves are a good source of protein, contain-
                                                        Cassava                                                      85




Table 1. Typical composition of cassava products (g kg    1   dry matter).

                               DM(%)         CP          CF           Ash        EE         NFE             Ca      P

Fresh leaves, 4 weeks            15.3       24.8        18.3          8.5       5.2        43.2             0.98   0.52
Fresh leaves, 8 weeks            16.1       24.1        26.0          8.0       5.0        39.9             0.99   0.56
Stem                                        10.9        22.6          8.9       9.7        47.9             0.31   0.34
Fresh roots                      32.1        3.9         4.9          4.8       1.0        85.4             0.09   0.12
Fresh peel                       27.9        5.3        21.0          5.9       1.2        66.6             0.31   0.13
Pomace                           83.5        2.2        26.9          3.4       0.6        66.9             0.68   0.05

CF, crude fibre; CP, crude protein; DM, dry matter; EE, ether extract; NFE, nitrogen-free extract.

             Table 2. Digestibility (%) and ME content of cassava.

                                               CP          CF           EE        NFE       ME (MJ kg 1)

             Ruminants
                   Leaves                     57.0        39.0         54.0       71.0               9.18
                   Tubers                      –          53.0         51.0       90.0              12.23
             Poultry
                   Leaf meal                  63.0                                                   7.80
             Pigs
                   Leaf meal                                                                         9.70
                   Tubers                     91.6                                                  14.57


ing 25% crude protein (CP) and producing up                     is > 70% after 24 h. In rations, peel is offered
to 6 t CP ha 1. The CP content, and hence                       primarily as an energy source with a protein
feeding value, decreases as the leaves become                   supplement. Optimum value is obtained with
older (see Tables 1 and 2). Leaf protein has a                  a rapidly degradable protein to synchronize
high lysine content but is low in sulphur-con-                  energy and nitrogen release.
taining amino acids. In labour-intensive pro-                       Cassava pomace, the residue after extrac-
duction systems, leaf stripping can be                          tion of starch from cassava roots, has a crude
practised to provide supplementary fodder for                   fibre (CF) content similar to leaves but is low
ruminants. However, removal of leaves can                       in protein, fat and minerals. Although it can
reduce root yields, and the use of leaves from                  be used as a ruminant feed, it is more com-
bitter varieties can result in HCN toxicity. Sun                monly fed to non-ruminants.          (LR, JKM)
drying of leaves may reduce the HCN con-
tent. Cassava foliage is usually used as a sup-                 Further reading
plement to grass fodder to increase dietary                     Devendra, C. (1988) Non-conventional Feed
protein levels. The use of 0.5% leaf in layer                      Resources and Fibrous Agricultural Resources.
rations will provide carotene for enhanced                         IDRC/Indian Council for Agricultural Research,
yolk colour. Inclusion rates of up to 150 g                        Ottawa, Canada.
kg 1, and 300 g kg 1 for growing pigs, can                      D’Mello, J.P.F. and Devendra, C. (eds) (1995) Tropi-
                                                                   cal Legumes in Animal Nutrition. CAB Interna-
be used with the addition of methionine and
                                                                   tional, Wallingford, UK.
an energy source. Dried leaf meal is bulky,                     Hahn, S.K., Reynolds, L. and Egbunike, G.N. (eds)
and pelleting is recommended for chick feed.                       (1992) Cassava as Livestock Feed in Africa.
    Silage can be made from the whole cas-                         IITA/ILCA, Ibadan, Nigeria.
sava plant. Cassava peel, a by-product from                     Robards, G.E. and Packham, R.G. (1983) Feed
the processing of roots for human use, can                         Information and Animal Production. Common-
also be used for animal feed. Peel is rarely fed                   wealth Agricultural Bureaux, Farnham Royal, UK.
fresh, because of high levels of cyanogenic
glycosides, which are reduced by sun drying,                    Castor bean (Ricinus communis L.)
ensiling and fermentation. Rumen DM                             A variable species, appearing as an annual
degradability of dried or ensiled cassava peel                  herb in temperate climates and, in tropical
86                                                   Castor bean




areas, as a perennial tree with leaves deeply                    Catabolism          Catabolism       (sometimes
divided into six fingers. Each spiny outer shell                  katabolism) refers to cellular metabolic
contains three seeds (beans) which can be                        processes leading to the systematic enzymatic
removed after drying. The bean is the source                     breakdown of molecules. These processes dif-
of castor oil, with a mechanical extraction rate                 fer from the extracellular breakdown of mole-
of around 66%. Approximately 60,000 t of                         cules called digestion, which occurs in the
castor bean meal are produced annually in                        intestinal tract. For example, the catabolism
India. Castor bean meal contains 0.22% ricin,                    of amino acids in the liver leads to the recov-
a toxin, which can be deactivated by steam                       ery of amino acid nitrogen in urea, while the
treatment (5 kg cm–2 for 15–30 min). Alter-                      digestion of protein in the intestinal tract leads
natively the meal can be boiled for 10 min in                    to free amino acids.                        (NJB)
three times its own volume of water, the water
discarded and the process repeated. The wet                      Cataract         A common degenerative con-
meal can be air dried at 70–80°C. Detoxified                      dition of the ocular lens in which the crys-
meal is a good source of protein and energy                      talline lens becomes opaque to varying
for ruminants, and can be included in concen-                    degrees. It commonly arises during diabetes or
trate mixtures for sheep at a level of 10%.                      some forms of poisoning. Cataracts are
Poultry appear to be less affected by ricin                      defined relative to the portion of the lens that
than mammals, and up to 40% of detoxified                         is opaque, aetiology, degree of change over
meal can be included in their rations.      (LR)                 time, degree of opacity and relationship to
                                                                 other intraocular pathological changes such as
Further reading                                                  adhesions between the lens capsule and iris.
Devendra, C. (1988) Non-conventional Feed                        Cataracts result from degeneration of the lens
   Resources      and     Fibrous     Agricultural               epithelium or changes in the osmotic status of
   Resources. IDRC/Indian Council for Agricul-                   the lens cortex allowing excess water to
   tural Research, Ottawa, Canada.                               invade the lens crystal.                   (DS)
Gohl, B. (1981) Tropical Feeds. FAO Animal Pro-
   duction and Health Series, No. 12. FAO, Rome.                 Catecholamines         A group of neuro-
                                                                 active amines. Dopamine, norepinephrine
Castration         Removal of the testes of a                    and epinephrine are derived from tyrosine
male animal by surgery or by chronic inter-                      via its hydroxylation to L-dopa (L-
ruption of the vascular and nerve supply to                      dihydroxyphenylalanine). Further metabo-
the testes and scrotum. Rendering the testes                     lism of L-dopa leads to the production of
dysfunctional by surgical or chemical means.                     these three catecholamines. They are syn-
                                        (MMit)                   thesized mainly in the adrenal medulla but
See also: Sex differences                                        norepinephrine, for example, is made in

Table 1. Typical composition of castor bean products (% dry matter).

                               DM(%)         CP          CF          Ash         EE         NFE            Ca      P

Castor bean meal,
     mechanical extraction                  34.8        33.2         10.4       10.6       32.2
Castor bean meal,
     solvent extraction          92.0       38.5        32.3          7.1        1.0       21.1            0.76   0.87

CF, crude fibre; CP, crude protein; DM, dry matter; EE, ether extract; NFE, nitrogen-free extract.

             Table 2. Digestibility (%) and ME content of castor bean.

                                               CP          CF           EE        NFE       ME (MJ kg 1)

             Ruminants
                 Castor bean meal             80.8         8.9         92.9       43.4              7.75
                                               Cattle                                               87




other organs and in nerve endings. In               of diet for juvenile and subadult fish. These
Parkinson’s disease there is a deficiency of         diets also typically contain relatively high lev-
dopamine synthesis.                   (NJB)         els of soluble carbohydrate from cereal grains
                                                    and grain by-products.                    (DMG)
Catfish         A rather large group of (princi-     See also: Aquaculture; Freshwater fish
pally) freshwater fishes characterized by a
body with no scales, or else covered with           Further reading
bony plates, and a head with up to four pairs       National Research Council (1993) Nutrient
of barbels. Catfish of the families Ictaluridae         Requirements of Fish. National Academy
and Clariidae are the major species estab-             Press, Washington, DC, 114 pp.
lished in aquaculture. The channel catfish           Robinson, E.H. and Wilson, R.P. (1985) Nutrition and
(Ictalurus punctatus) is native to North Amer-         feeding. In: Tucker, C.S. (ed.) Channel Catfish
ica and has constituted a major aquacultural           Culture. Elsevier, Amsterdam, pp. 323–404.
enterprise in the USA for over three decades.
Walking catfish of the genus Clarius, which          Catheter          A tube introduced into a body
are native to Africa and Asia, have been cul-       cavity for the withdrawal of fluid or for the intro-
tured in these countries as well as in Europe.      duction of substances. A catheter is commonly
    The nutritional requirements of channel         placed in a vein to obtain repeated blood sam-
catfish have been extensively studied with as        ples or in the bladder for the complete collec-
many as 40 nutrients in all of the major            tion of urine. A larger tube introduced into the
groups having been demonstrated to be nec-          gut is normally called a cannula.             (DS)
essary for normal metabolic functions. Cur-
rently there is less nutritional information        Cation: An ion with a positive charge. (NJB)
available for Clarius catfish. Catfish in both        See also: Acid–base balance
genera are omnivorous in their feeding behav-
iour and will consume a variety of food organ-      Cattle        Cattle belong to the order Artio-
isms in nature. As such, these fish generally        dactyla (even-toed ungulates), suborder Rumi-
can thrive on prepared diets composed of            nantia, family Bovidae, subfamily Bovinae and
plant-derived feedstuffs with relatively low pro-   tribe Bovini. Bovinae are characterized by the
tein concentrations ranging from 28 to 32%          presence of hollow horns and Bovini by their




Harvesting catfish from a freshwater pond.
88                                             Cattle




large size. Commercially important species          (somatotrophin) promotes milk production by
among the tribe Bovini are found in the genus       diverting the products of digestion and inter-
Bovina (mainly Bos species). Humpless cattle        mediary metabolism away from tissue deposi-
(Bos taurus) predominate in northern temper-        tion and towards the mammary gland during
ate latitudes whereas humped cattle (Bos indi-      periods of negative energy balance, character-
cus) inhabit the more arid regions of the           istic of early lactation. This is achieved, in
world. These two species can interbreed to          part, by inhibiting the insulin-mediated uptake
produce fertile offspring. Other species in this    of glucose by skeletal muscle, and by inhibit-
genus include Bos grunniens (domestic yak),         ing the ability of insulin to stimulate lipogene-
Bos javanicus (Bali cattle) and Bos frontalis       sis. Exogenous bovine somatotrophin (bST)
(domesticated gayal), found in Asia.                has been shown to result in a 12–35%
    Domestication of these species involved         increase in milk yield in high-yielding dairy
selection for functional traits such as docility,   cows (Zinn and Bravo-Ureta, 1996).
mature size, draught, milk production and               Voluntary feed intake in ruminants is highly
muscularity, as well as type traits such as coat    variable and difficult to predict. Intake (per unit
colour and polledness. Differential selection for   liveweight) is affected by a number of animal-
such traits resulted in the formation of breeds,    and feed-related factors. The principal animal-
i.e. animals of common origin with certain dis-     related factors include genotype (generally
tinguishing characteristics passed uniformly        dairy genotypes have a higher intake capacity
from one generation to the next. Adaptation         than beef genotypes; and high-yielding cows
to local environmental conditions through nat-      eat more than low-yielding cows), body com-
ural selection also occurred. For example, the      position (thinner cows eat more than fatter
N’Dama breed (Bos taurus), resident in West         cows) and physiological status (lactating cows
Africa, developed resistance to trypanosomia-       eat more than non-lactating cows). Principal
sis (sleeping sickness) spread by the tsetse fly.    feed-related factors include the dry matter con-
    In developed countries, particularly those in   tent of the feed, its particle size, cell wall con-
North America and Europe, cattle have been          tent and rate of digestion, and a variety of
classified by utility, where selection has           factors that influence conditions within the
favoured the production of either meat or milk      rumen. All these factors interact during early
(Buchanan and Dolezal, 1999). Mature size           lactation to limit nutrient intake and the prod-
can vary considerably within each class and         ucts of rumen fermentation relative to the
this, together with the genetic potential for       metabolic requirements of the cow, thus plac-
milk production, can have a significant bearing      ing greater emphasis on the mobilization of
on the animal’s metabolizable energy (ME)           body tissues. As a consequence, the high-yield-
requirements for maintenance (0.40–0.55 MJ          ing cow is very sensitive to a number of meta-
ME kg–1 Wt0.75 for non-lactating beef cows;         bolic disorders, particularly during early
0.50–0.65 MJ ME kg–1 Wt0.75 for lactating           lactation when demands placed on the ani-
beef cows; and up to 0.77 MJ ME kg–1 Wt0.75         mal’s metabolism are at their greatest. For
for lactating dairy cows), so determining their     example, the excessive mobilization of body
suitability to specific nutritional environments     lipids during this period, combined with an
(Sinclair and Agabriel, 1998).                      inadequate dietary supply of glucogenic pre-
    The rapid increase in milk yield during the     cursors, can result in the incomplete oxidation
first 4–8 weeks of lactation normally requires       of fatty acids, causing an accumulation of
the cow to meet her metabolic requirements          ketone bodies in the blood that can ultimately
through a combination of dietary intake and         lead to clinical ketosis. In time, the accumula-
body tissue mobilization. The metabolic             tion of fatty acid deposits in the liver can
demands during this period are carefully regu-      impair liver function, resulting in various disor-
lated through the combined effects of a num-        ders and culminating in fatty liver syndrome.
ber of homeorhetic and homeostatic                  Other common metabolic disorders in the peri-
hormones that collectively coordinate the           parturient cow include milk fever, the clinical
processes of lactogenesis, voluntary feed           manifestation of calcium deficiency. Calcium
intake and nutrient partitioning in support of      metabolism in mammals is tightly regulated
galactopoiesis. Of these, growth hormone            and, whilst total bone calcium levels are high,
                                             Cattle feeding                                             89




only the most recently deposited fraction of          Chamberlain, A.T. and Wilkinson, J.M. (1996)
bone calcium can be mobilized. Factors that              Feeding the Dairy Cow. Chalcombe Publica-
predispose cows to milk fever include age                tions, Lincoln, UK.
(older cows are more prone than younger               National Research Council (1996) Nutrient
cows) and calcium supplementation during the             Requirements of Beef Cattle, 7th rev. edn.
                                                         National Academy Press, Washington, DC.
immediate pre-partum period; restricted intake
                                                      Sinclair, K.D. and Agabriel, J. (1998) The adapta-
during this time can increase the efficiency of
                                                         tion of domestic ruminants to environmental
absorption following parturition.                        constraints under extensive conditions. Annales
    The inability of the high-yielding cow to            de Zootechnie 47, 347–358.
derive all the nutrients necessary to sustain         Zinn, S.A. and Bravo-Ureta, B. (1996) The effect of
her metabolic requirements during early lacta-           bovine somatotrophin on dairy production, cow
tion means that frequently she will benefit               health and economics. In: Philips, C.J.C. (ed.)
from dietary components that resist microbial            Progress in Dairy Science. CAB International,
fermentation in the rumen. These forms of                Wallingford, UK, pp. 59–85.
starch, lipid and proteins are largely digested
and absorbed in the lower gut. Young and              Cattle feeding           Digestion in cattle
rapidly growing cattle may also benefit from           involves an initial microbial fermentation in
such supplements, particularly from protected         the rumen followed by digestion of the micro-
sources of protein. In these circumstances, the       bial biomass and previously undigested feed
efficiency of absorption of amino acids and            by enzymes produced further down the gas-
the production response will depend on the            trointestinal tract. The maintenance of effec-
biological value of the rumen-undegradable            tive rumen microbial function requires
protein fraction of the supplement.                   adequate fibre, energy, protein, minerals and
    Production responses in growing stock to          vitamins in the diet. The nutrient requirements
concentrate supplementation normally arise            of high-yielding dairy cows cannot be met
through alterations in the molar proportions          from microbial digestion of coarse fibre alone,
of the principal volatile fatty acids within the      and high quality supplements must be fed (see
                                                      Cow feeding). Cattle for beef production do
rumen, high-grain diets resulting in increased
                                                      not have to be fed high quality diets, but the
propionate production from the rumen. With
                                                      fast growth and rapid turnover that can be
the possible exception of protected sources of
starch, older and more slowly growing cattle
seldom benefit from ‘rumen-protected’ sup-
plements, the products of rumen fermentation
normally being sufficient to meet their require-
ments for maintenance and growth. Further
exceptions to this rule, however, arise when
young cattle (particularly non-castrated males)
undergo compensatory growth or have an
abnormally high potential for lean tissue
growth, e.g. the doubled-muscled breeds.
                                          (KDS)


References and further reading
AFRC (1993) Energy and Protein Requirements
   of Ruminants. An advisory manual prepared
   by the AFRC Technical Committee on
   Responses to Nutrients. CAB International,
   Wallingford, UK.
Buchanan, D.S. and Dolezal, S.L. (1999) Breeds of
   cattle. In: Fries, R. and Ruvinsky, A. (eds) The
   Genetics of Cattle. CAB International, Walling-    Grazing is a central feature of many systems of
   ford, UK, pp. 667–695.                             cattle production.
90                                             Cattle feeding




achieved when supplements of energy and                 or the cost of finishing will be too great; silage
protein are fed may make this a more prof-              alone or clean straw and a small amount of
itable system than low-input production. Cat-           concentrates (c. 1.5 kg per head per day)
tle production systems range from extensive             would be appropriate. They may only grow at
suckled calf production to intensive cereal-            about 0.5 kg day 1 during winter but they will
based beef production.                                  compensate for this when they are at pasture.
    Suckler cows are usually kept on marginal           The grazing cattle can be sold when they are
land that cannot be used for the production of          finished or, in an emergency, when the grass
high value crops (e.g. mountainous or arid              availability is very low.
regions). The demands of the cows can be met                In America there is a large supply of suck-
from low-quality fodder, which is all that can be       ler cows on rangeland producing suckled
grown in such regions. In the UK, a medium-             calves for finishing. The feedlots usually finish
sized suckler cow has an energy requirement of          the store cattle intensively over a 6-month
about 100 MJ day 1 during winter. This is pro-          period. Local arable farmers may be con-
vided by about 8 t of silage for an autumn-calving      tracted to produce whole-crop barley silage
cow, whereas the requirements of a spring-calv-         with some chopped hay or straw and rolled
ing cow are likely to only be about two-thirds of       barley for the final fattening period.
this amount. This means that more land must be              Calves from dairy herds are normally
reserved for forage conservation for autumn-calv-       housed inside and fed conserved feed. High
ing cows – perhaps 60% of the grassland area            growth rates in housed cattle are best
for two cuts, compared with perhaps 40% for a           achieved by offering high quality forage ad
spring-calving herd. In many hill farms, setting        libitum. If this is not available, whatever for-
such a high proportion of land aside for conser-        age is available should be supplemented with
vation, when the grass growing season is short          a cereal, such as rolled barley, the quantity
anyway, is not possible due to constraints of the       depending on the quality of forage fed. Suffi-
terrain and the need for grazing. The introduction      cient concentrate must be fed to allow the
of machinery for making and handling silage in          cattle to finish indoors, if this is what was
big bales has assisted many farms in moving from        planned. If insufficient concentrate is fed on
making hay, with all its difficulties in wet areas, to   a daily basis early on in the winter, the
conserving fodder as silage.                            farmer may actually end up providing more
    The suckled calves produced on marginal             concentrates in total, because marketing of
farms are usually sold for fattening to farms           the cattle cannot start in the mid-winter
where better quality food can be grown.                 period. The successful operator knows how
These ‘store’ cattle can be fed a variety of            fast the cattle are growing and feeds supple-
diets, but any change in diet should be intro-          ments accordingly, so that the cattle can be
duced gradually. High quality forages, espe-            marketed at the right time and plans can be
cially maize silage, root crops and cereals, are        made for the next season’s cattle. If cattle
most likely to be included in the ration, but           are reared over a longer period, such as a
waste products from the vegetable industry,             24-month system that finishes the autumn-
such as stock feed potatoes, can be included            born cattle off pasture in their second sum-
and reduce the cost of the ration. The skill of         mer, it must be ensured that not too much
the farmer in buying low-cost feeds, and cat-           expensive food is fed during winter if the sys-
tle, undoubtedly plays a part in the profitabil-         tem is to be profitable.
ity of the store-finishing enterprise.                       Cattle may also be fed indoors throughout
    The cattle can be finished indoors in win-           their life, mostly on conserved forages or
ter, in which case they are usually fed good            cereal-based diets. Grass and maize silages are
quality forage and a limited amount of con-             most common, or a mixture of the two, since
centrates, perhaps 2–3 kg per head per day.             the high protein concentration in grass will
Alternatively they can be finished at pasture. If        complement the high energy content of
the cattle are purchased in early or mid-win-           maize. Roots can be fed, but not usually at
ter, this will only be applicable to animals of         more than one-third of the diet. Calves are
late-maturing breeds. In this case they should          usually reared on hay initially and transferred
not be fed a high quality ration in the winter          to a silage diet at 8–10 weeks. Protein supple-
                                            Cell walls                                           91




ments can be kept at a constant level, so that     protein, lignin and cutin. The cell walls of
as the cattle grow they consume more silage        grasses also contains silica. The principal
and the protein content of the ration is           polysaccharides are cellulose, arabinoxylans
reduced. The system of feeding a predomi-          and pectin, but there is large diversity in poly-
nantly cereal diet is common where the two         saccharide composition among plant species.
main inputs, cereals and calves, are inexpen-      Plant extensin is a fibrous protein associated
sive relative to the finished product. The main     with the deposition of the cell wall. Lignin is a
feeding-related disorders that occur are rumen     polyphenolic compound that imparts rigidity
acidosis, bloat, liver abscesses and laminitis.    to the cell wall. Cutin is composed of higher-
                                         (CJCP)    molecular-weight alcohols and gives the sur-
See also: Cow feeding                              face of the cell wall a waxy appearance.
                                                       The compositions of the cell walls of
Cauliflower          Cabbage flower (caulis),        grasses and legumes differ. In general, grasses
Brassica oleracea, of which there are many         usually have a higher percentage of cell wall
varieties, has a compact white head of fleshy       in the above-ground biomass than legumes at
flower stalks and is eaten by humans as a veg-      a similar stage of maturity. However, legumes
etable. Cauliflowers are available year-round       usually have a greater percentage of lignin in
and are particularly plentiful in spring and       the cell wall than grasses. The polysaccharides
autumn. They have a very high vitamin C            in the cell walls of grasses are composed of
content and are rich in potassium, fibre and        approximately equal ratios of cellulose to ara-
folate. Surplus production can be fed fresh to     binoxylans and other heteropolysaccharides,
cattle and sheep. Cauliflower is a good source      whereas in legumes the ratio of cellulose to
of protein, has no fat but contains high levels    other heteropolysaccharides is much higher.
of natural sugar and dietary fibre. Typical dry     The composition of the cell wall also varies
matter (DM) content of cauliflower is               widely among specific plant parts and cell
120–130 g kg 1 and the nutritive com-              types within each cell tissue. Cells that are
position (g kg 1 DM) is crude protein              involved in photosynthesis have thin primary
230–240, crude fibre 120–125, ether extract         cell walls with little or no lignin. Cells that
20–25, ash 115–120, neutral detergent              have a structural role have thickened sec-
fibre 290–295 and starch 5–8, with ME               ondary cell walls that are highly lignified.
11.5–12 MJ kg–1 DM.                     (JKM)          At an early stage of development, the
                                                   plant cell wall has a low content of lignin and
Celery         Celery (Apium graveolens L.) is     the cell wall polysaccharides are highly
widely grown for human consumption. It has         degradable by microbial enzymes. As the
recently been introduced into the tropics for      plant cell matures, the contents of lignin,
cultivation at higher altitudes. Surplus produc-   cutin and silica increase and the degradability
tion may be available for use as animal feed.      of the cell wall polysaccharides decreases.
The leaves are rich in protein and carotene;       These changes in the composition and
they have been used up to a rate of 10% of         degradability (digestion) of the cell wall are
the diet in chickens and can effectively replace   responsible for decreases in digestible energy
lucerne meal. In Africa, the dry matter con-       as forages mature.
tent of fresh leaves is 110 g kg 1 and the             Mammals and other animals do not have
nutrient composition (g kg 1 DM) is crude          enzymes that hydrolyse cell wall polysaccha-
protein 272, crude fibre 35, ash 190, ether         rides but obtain energy from cell walls through
extract 69, neutral detergent fibre 434, cal-       fermentation of polysaccharides by symbiotic,
cium 27 and phosphorus 17.                 (JKM)   anaerobic microorganisms that reside mainly
                                                   in sacculated organs of the digestive tract,
Cell walls         Heterogeneous macromolec-       such as the rumen, colon or caecum. These
ular structures that are exterior to the plasma    microbes possess a diversity of enzymes that
membrane and give rigidity and shape to the        break down the cell wall polysaccharides. The
cell. Bacteria, fungi and plants have cell walls   monosaccharides undergo fermentation to
of different compositions. Plant cell walls are    volatile fatty acids (VFAs) that are absorbed
composed of a mixture of polysaccharides,          and used by the host for energy metabolism.
92                                            Cellobiose




   ‘Cell wall’ and ‘fibre’ are often used as syn-     allows the cellulolytic enzymes to be concen-
onyms. This may lead to confusion: many              trated on the substrate, restricts access to the
non-fibrous polysaccharides that do not occur         site of hydrolysis and end-products and pro-
in plant cell walls are referred to as ‘dietary      tects the enzymes from ruminal proteases.
fibre’ in the human nutrition literature because      Electron micrographs of fibrolytic bacteria and
they are not digestible by mammalian                 fungi adhering to plant cell walls show the
enzymes but require fermentation to yield            material being gradually eroded. Considering
energy. Therefore, caution is required in the        the highly complex nature of the substrate
use of the terms.                         (JDR)      involved, this implies that a range of specific
                                                     fibrolytic enzymes are released simultaneously.
Cellobiose         A disaccharide, 4-O- -D-          In ruminants, the primary site of cellulolytic
glucopyranosyl-D-glucose, C12H22O11, the             activity is the reticulorumen, followed by the
basic structural unit of cellulose and a product     caecum, while in horses and pigs this occurs in
of the hydrolysis of cellulose by cellulase. The     the enlarged colon.                       (FLM)
stereochemistry of cellobiose allows the for-
mation of two intramolecular hydrogen bonds.         Cellulose          A homopolysaccharide of
Cellobiose is often used as a substrate in           glucose in which glucose residues are linked
microbiological tests for cellulase activity.        between carbon 1 of one glucose residue and
                                             (JDR)   carbon 4 of the adjacent glucose ( -D-glucopy-
                                                     ranose– -D-glucopyranoside linkages); this
Cellulase        An enzyme that hydrolyses the       linkage is written as (1→4). Cellulose is the
  (1→4)-O-glycosidic linkages in cellulose. Cellu-   main polysaccharide in the plant cell wall. It is
lases occur in bacteria, fungi and plants but not    the most abundant natural polymer on the
in animals. In bacteria and fungi, cellulases        earth’s surface and, were it not degraded and
degrade plant cellulose to glucose, cellobiose       converted to CO2 by microorganisms, atmos-
and oligoglucans to derive energy for growth         pheric CO2 would be rapidly depleted by the
and reproduction. Cellulase in bacteria is located   fixation of CO2 into cellulose by plants. The
in protuberances on the cell surface called cellu-   macromolecular structure of cellulose is
losomes. These structures are involved in the        formed by intramolecular and intermolecular
attachment of bacteria to plant cell walls and are   hydrogen bonds that give cellulose its fibrous
required for normal cellulase activity.      (JDR)   properties. Cellulose is organized into bundles
                                                     of microfibrils that form a network around the
Cellulolytic microorganisms               As no      plant cell. At early stages of growth this net-
mammal secretes an enzyme complex capable            work is flexible and the cell structure is main-
of degrading cellulose, the symbiotic relation-      tained by turgor pressure and the resistance of
ship between the enteric fibrolytic microflora         the network. After the cell has elongated and
and herbivores is vital to the utilization of        lignin is deposited in the cell wall, the shape
fibrous plant material. Plant cell walls are          of the cell may become fixed.
degraded by a combination of bacteria, fungi             Animals do not have digestive enzymes
and protozoa, the first two groups accounting         that are capable of hydrolysing (1→4)-glyco-
for about 80% of the activity. The main cellu-       sides (cellulases) but symbiotic microorganisms
lolytic bacteria are Fibrobacter succinogenes,       of the digestive tracts do have cellulases and
Ruminococcus albus, R. flavifaciens and               degrade cellulose to volatile fatty acids. These
Butyrivibrio fibrisolvens. Among the fungal           acids are absorbed and metabolized by the
species are Neocallimastix frontalis, N. patri-      host. The rate of degradation of cellulose is
ciarum, Orpinomyces bovis and Piromyces              slow compared with other polysaccharides.
communis, while ciliate protozoa of the gen-         Microbial attachment to the surface of the cel-
era Diplodinium and Eudiplodinium degrade            lulose microfibrils is required for cellulose
cellulosic material by engulfment (phagocyto-        degradation to proceed.                    (JDR)
sis). In contrast to the weak opportunistic inter-
action of protozoa with plant material, the          Cereals        Those members of the
majority of cellulolytic bacteria and fungi form     Gramineae (grass) family that are cultivated
strongly associated colonies. This strategy          for their grain, which is primarily used for
                                           Chemical composition                                        93




human and animal food. The cereals most                 rated fatty acid found in the oils of cetaceans
commonly cultivated are barley (Hordeum                 (whale and dolphins) and fish.             (NJB)
sativum), maize (Zea mays), oats (Avena
sativa), wheat (Triticum aestivum), rice                Chelate         An association of two or more
(Oryza sativa), rye (Secale cereale), triticale         independently existing molecules or ionic
(hybrid of wheat and rye) and sorghum                   species to form a heterocyclic ring compound.
(Sorghum bicolor). Most of the proteins of              The new compound formed by this association
cereal grains are found in the endosperm                exhibits chemical and physical characteristics
(e.g. 72% in wheat) and their overall content           distinct from those of either parent compound
is influenced by a range of factors, including           or element. In biological systems chelates typi-
species, variety, fertilizer application, soil          cally involve a metal cation such as iron, cobalt,
fertility and climate. Protein concentrations           copper, magnesium or zinc bound to an organic
are typically 97–160 g kg 1 dry matter (DM)             compound via oxygen, nitrogen or sulphur ele-
for barley and wheat but lower for maize                ments. Examples include chelates such as
and oats. Cereal proteins are generally defi-            haemoglobin, chlorophyll and vitamin B12. Lig-
cient in essential amino acids, especially              and bonds vary from relatively stable covalent
lysine. In all cereal species the starch-rich           bonds to very unstable, highly ionic bonds
endosperm is the most important fraction,               between molecules. In animal nutrition, chelat-
both nutritionally and economically. The                ing compounds are used to sequester or stabilize
starch comprises amylose and amylopectin                metal ions. A common chelating agent is ethy-
and their ratio determines the quality of the           lenediaminetetraacetic acid (EDTA).         (TDC)
starch. The cell wall content (as NDF)
ranges from about 124 for wheat to 310 g
                                                        Chemical composition                Descriptions
kg 1 DM for oats. The animal feed industry
                                                        of the chemical composition of foods (and of
represents a major market for cereal grains,
                                                        plant and animal tissues) are largely based on
which contribute a large proportion of the
                                                        the proximate analysis scheme introduced by
energy supply to pigs, poultry and young
                                                        Henneberg and Stohman at the Weende Insti-
ruminants. Generally cereals make a lower
                                                        tute in Germany in about 1840. In this
contribution to the diets of ruminants.
Cereal by-products arise from a number of               scheme (see figure) food is considered to be
industries, including milling, brewing, distill-        composed of water and dry matter. The dry
ing and starch manufacture. Cereal by-prod-             matter consists of an inorganic fraction (min-
ucts play an important role in the diets of             erals and trace elements), represented practi-
ruminants owing to their greater capacity to            cally as ash, and an organic matter fraction
degrade fibre.                             (ED)          represented by the mass lost on combustion.
                                                        The organic matter in turn is composed of
Further reading                                         three classes of chemical compounds: lipids,
Givens, D.I., Clarke, P., Jacklin, D., Moss, A.R. and   carbohydrates and proteins.
   Savery, C.R. (1993) Nutritional Aspects of               The lipid consists of fats, oils and waxes,
   Cereals, Cereal Grain By-products and Cereal         which are mainly long-hydrocarbon-chain
   Straws for Ruminants. HGCA Research                  glycerol triesters (-CH2-)n. They are hydropho-
   Review No. 24. HGCA, London, 180 pp.
                                                        bic and insoluble in water but soluble in non-
MAFF (1990) UK Tables of Nutritive Value and
                                                        polar organic solvents. Total lipid can be
   Chemical Composition of Feedingstuffs.
   Rowett Research Services Ltd, Aberdeen, UK,          determined by a percolating extraction with
   420 pp.                                              solvent      in      a     Soxhlet     extractor.
                                                        Originally, diethyl ether was used and total
Ceruloplasmin              The US spelling of           lipid was therefore described as ether extract
caeruloplasmin.                                         (EE). The lipid components can be further
                                                        characterized by determining individual fatty
Cetoleic acid        cis-11-Docosenoic acid,            acids from gas chromatography of their
CH3·(CH2)9·HC=CH·(CH2)9·COOH, molecu-                   methyl esters (FAME-GC: fatty acid methyl
lar weight 338.6, shorthand designation 22:1            esters) or by high-pressure liquid chromatogra-
n-11, a long-chain 22-carbon monounsatu-                phy (HPLC) of intact triglycerides.
94                                       Chemical composition




       WATER                                        DRY MATTER (DM)
                         ASH                  ORGANIC MATTER (OM)

     Oven drying
      at 100°C                          LIPID               CARBOHYDRATE                  PROTEIN

                Furnace at 500°C      fats, oils,     sugars      starch      ‘fibre’   20 amino acids
                                       waxes
                   HCI digestion



                    Minerals            Ether    Reducing       Enzymatic      ‘CF’      ‘CP’ = 6.25N
                Na, K, Ca, Mg, P,      extract    sugars         methods       ADF        Kjeldahl-N
                       etc.            Solvent                                NDF          Dumas-N
                 Trace elements       extraction                              MADF
               Cu, Mn, Zn, Fe, etc.   (Soxhlet)                               NSP


     Empirical composition            C20H38O2       C6H12O6     C6H12O5     C6H12O5

     Approximate gross energy            39                         18                       23
     (MJ kg–1)

The proximate analysis scheme for plant and animal tissues.

    The protein content of foods can be esti-            ADF; and neutral detergent fibre, NDF) has
mated from the nitrogen content. Proteins                been developed to better characterize fibrous
contain, on average, 160 g N kg 1; hence                 cell wall constituents fed to ruminants. In starchy
crude protein (CP) is defined as N          6.25.         foods the Englyst non-starch polysaccharide
Total nitrogen has traditionally been deter-             (NSP) enzymatic procedure is more appropriate
mined by the Kjeldahl procedure (1883) but               for non-ruminant animals and humans. Enzy-
the Dumas method is also used. Methods of                matic or chromatographic methods can be used
estimating protein from nitrogen determina-              to measure individual monosaccharides, disac-
tion do not distinguish between protein and              charides and starch.
non-protein nitrogen (NPN). Amino acid com-                  Major minerals (Na, K, Ca, Mg, P) and trace
position can be determined on hydrolysates               elements (Fe, Cu, Mn, Zn, Co, Mo, etc.) can be
by ion exchange or HPLC methods.                         determined by flame emission spectroscopy
    The carbohydrate fraction of foods consists          (FES), atomic absorption spectroscopy (AAS),
of soluble sugars (mainly monosaccharides and            or inductively coupled plasma spectroscopy
disaccharides), starch and non-starch polysac-           (ICP) conducted on hydrochloric acid solutions
charides (NSP), imperfectly described as ‘fibre’.         of the ash from feeds. Modern ICP spectrome-
In the Weendes system the carbohydrate frac-             ters can measure as many as 26 elements
tion was considered to consist of crude fibre and         simultaneously on one ash solution.
nitrogen-free extractives (mainly starch and sim-            The gross energy (GE) value of foods is
ple sugars). The term ‘fibre’ is used for a com-          determined by combustion in an adiabatic
plex range of plant cell wall constituents that          bomb calorimeter. It may also be approximated
may or may not include lignin, which is not a            from the lipid, nitrogen and carbohydrate
carbohydrate but a complex aromatic polymer              determination, using average heats of combus-
of phenylpropane subunits. Many methods for              tion of those components. It will be appreci-
determining and characterizing fibre have been            ated that a full characterization of the chemical
developed from the original much-criticized              composition of a food is a lengthy, complex
acid–alkali crude fibre (CF) method. In forages           and costly procedure that can never be com-
the Van Soest scheme (acid detergent fibre,               plete. Gross composition is ‘operationally
                                           Chemical probiosis                                          95




defined’ and overlap between the classes of             lectins themselves may have a major influence
lipid, carbohydrate and protein (e.g. glycolipids,     on the turnover of the intestinal cells and the
lipoproteins) means that measured constituents         effect of lectins in relation to infection by path-
may not sum to 100% in any given food.                 ogenic bacteria depends on the specificity of
    Because of the many costly analyses                the lectin as well as its concentration. Thus,
required to determine the composition of               dietary lectins can both enhance and reduce
foods, a newer method of analysis, near                colonization by pathogenic bacteria.
infrared spectroscopy (NIRS), attempts to                  In an alternative form of chemical probio-
characterize the composition of food from its          sis, bacterial adhesion is inhibited by feeding
spectral signature in the near infrared. Instru-       simple or complex carbohydrates that have a
mental methods of food analysis have now               terminal structure that closely mimics the car-
largely replaced extractive wet chemical meth-         bohydrate side chains of the bacterial recep-
ods for food analysis.                        (IM)     tors on the gut wall. While dietary lectins
                                                       actually occupy the same sites as the bacterial
References and further reading                         adhesins, the complementary saccharides act
Horwitz, W. (ed.) (2000) Official Methods of
                                                       by competing with them.
   Analysis of AOAC International, 17th edn.
   AOAC International, Arlington, Virginia.                Chemical probiosis is an alternative to
Kirk, R.S. and Sawyer, R. (eds) (1991) Pearson’s       probiosis by the addition of live bacteria
   Composition and Analysis of Food, 9th edn.          (called probiotics) which also function by a
   Longman Scientific & Technical, Harlow, UK,          competitive exclusion of pathogenic bacteria.
   708 pp.                                             Thus, both methods may help to maintain
MAFF–ADAS (1986) The Analysis of Agricultural          normal commensal flora (the resident non-
   Materials, 3rd edn. Reference Book 427.             pathogenic flora).                              (SB)
   HMSO, London, 248 pp.
                                                       See also: Prebiotic; Probiotics
Moughan, P.J. (2000) Feed Evaluation: Principles
   and Practice. Wageningen Pers, Wageningen,
   The Netherlands, 285 pp.                            Chemical score            An evaluation system
Southgate, D.A.T. (1991) Determination of Food         used to assess the relative value of a single
   Carbohydrates, 2nd edn. Elsevier Applied Sci-       protein or mixture of proteins (and amino
   ence, New York, 232 pp.                             acids) to be used in a diet. A value is obtained
                                                       by assessing the amino acid pattern (usually
Chemical probiosis              The control of the     mg amino acid g –1 N) of the protein(s) in rela-
gastrointestinal microflora, especially of              tion to an established reference amino acid
bacterial pathogens, by dietary substances that        pattern. This pattern may be developed from
interfere with microbial adhesion. Many bac-           the estimated amino acid requirements of the
terial pathogens adhere to the gut surface by          animal in question, or from the pattern of
the binding of their fimbriae to sugar moieties         high quality protein, such as egg protein. The
on the epithelial surface. The fimbriae contain         value of a protein is not constant, because
specific lectins called adhesins: this binding          amino acid requirements vary with species
mechanism is essential for adhesion and infec-         and with purpose (maintenance, growth, milk
tion by many pathogenic bacteria that need to          or egg production). The score is calculated by
resist peristalsis in the intestine in order to col-   dividing the amount of each indispensable
onize it.                                              amino acid in the diet by the amount of the
    Lectins are proteins capable of specific and        same amino acid in the reference pattern: the
reversible binding to sugar moieties. Suitable         score is the lowest of these ratios. For exam-
lectins for inhibition of bacterial adhesion can       ple, if the lowest score is for lysine (making it
be isolated from bacteria, e.g. from those             the first limiting amino acid) and the amount
pathogenic bacteria that cause infections. Cer-        of lysine (mg g 1 N) in the diet is 80% of that
tain plant lectins have similar affinities to those     in the reference pattern, the chemical score is
of the specific bacterial lectins involved in           80%. This protein evaluation scheme assumes
adhesion of the bacteria to intestinal epithelial      accurate estimates of the amino acid content
cells and these can also be isolated and used to       of the proteins involved and that dispensable
inhibit bacterial adhesion. On the other hand,         amino acid nitrogen is not limiting.       (NJB)
96                                    Chemical treatment of feeds




Chemical treatment of feeds                Straws,    tion (g kg 1 DM) is crude protein 12–16, neu-
high-moisture grains and forages may be               tral detergent fibre 180, lignin 41, acid deter-
chemically treated when making hay, silage or         gent fibre 146, ether extract 70, WSC 95 and
alkalage to ensure preservation without deteri-       starch 53, with ME 13.7 and gross energy
oration, to improve nutritive value, or both.         20.6 MJ kg–1 DM.                         (JKM)
    Alkali treatment in the form of sodium
hydroxide, ammonia or urea has been used              Chick        A young bird, especially one that
on a number of low-quality forages, including         has recently hatched. The term is frequently
straws, husks and hays. It is carried out in an       used to describe young birds that are still cov-
enclosed container and results in an end-prod-        ered by down and have not yet developed a
uct with a pH of 10–11. Alkali reduces the            complete feather cover.                   (SPR)
number of ester linkages between lignin and           See also: Broiler chickens
cell wall carbohydrates and increases the
digestibility from c. 55% before to 65% after         Chicken          Domestic fowl bred for either
treatment. Urea is also used in the production        their meat or eggs. The modern commercial
of alkalage from whole-crop cereals. This             layer falls into two main categories: white
product is akin to silage with the exception          breeds and brown breeds. Most of the eggs
that it is alkaline and not acidic. The urea pre-
                                                      consumed worldwide are white. This is
serves the crop by releasing ammonia, which
                                                      because the white layer is a more efficient and
inhibits the activity of undesirable microorgan-
                                                      prolific genotype. Most modern breeds pro-
isms within the clamp.
                                                      duce in excess of 20 kg of egg mass by 76
    Hydrochloric, sulphuric and formic acids are
                                                      weeks of age with a feed conversion ratio
used in the preservation of green crops as
                                                      (FCR) of just over 2.0. Brown hens can also
silage. These inhibit microbial activity within the
                                                      produce about 20 kg of egg mass output, over
silo, preserving the forage by direct acidification.
                                                      the same time period, but require more food
    Recently the longer-chain organic acids
                                                      to do so. They are typically heavier birds and
propionic, caproic and acrylic have been
included in acid mixtures to inhibit yeasts and       therefore have a higher maintenance require-
moulds associated with the aerobic spoilage of        ment. The other consequence of being heavier
silage. Propionic acid is used in the storage of      is that they lay larger eggs; but, as the total
high-moisture cereal grains (moisture content         mass of egg they lay is similar to that of white
20–30%) for the same purpose. Sodium ben-             birds, they lay fewer eggs. Today’s laying hen
zoate is used in the preservation of a variety        can lay 329 eggs in 392 days, which is almost
of feeds for its anti-microbial activity. Sul-        85% lay, or the equivalent of laying 6 days out
phites and bisulphites are also used in the           of every 7, throughout the bird’s life. Brown
preservation of silages. These generate sul-          hens lay eggs of an average weight of 63 g on
phur dioxide, which is toxic to many spoilage         an average 115 g of feed per day.
microorganisms.                               (DD)         With increased commercialization has
                                                      come greater intensification, leading to large
Chestnut          The reddish brown edible nut        units with environmentally controlled houses.
of sweet chestnut (Castanea sativa), primarily        Due to disease problems such as coccidiosis in
harvested for human consumption. When                 extensive systems, hens were transferred into
used as animal feed, chestnuts may be ground          cages where they could be spatially separated
or crushed and made into meals or occasion-           from their faeces. This was done on the basis
ally pellets. They can be fed to most species         of bird welfare. Today, birds are being
of livestock but the level of inclusion for rumi-     returned to the range because cages raise
nants is limited by the high oil content. Like        concerns about the birds’ welfare. Modern
all nut products, they can be contaminated            medicines and vaccines mean that birds can
with aflatoxins and are therefore subject to           be kept in large colonies, out of doors and on
feed regulations. Treatment may be required           the same pastureland in successive years.
to remove such contamination. The typical             Hens are also kept indoors on the floor in
dry matter (DM) content of chestnuts is               what have become known as ‘barn’ or ‘deep
920–930 g kg 1 and the nutrient composi-              litter’ systems. This allows full environmental
                                              Chicken                                            97




control as with a cage system but enables the       organizations the benefits of yield and growth
hens to display their natural pecking order,        characteristics outweighed those of broiler
roam, perch and dust-bathe.                         numbers. However, independent hatcheries
    Hens kept on extensive production sys-          preferred the light breeds that laid more eggs
tems, such as free-range or barn, consume           and hence gave more chicks for them to sell.
greater quantities of food for the same egg         Also in certain markets around the world peo-
mass output compared with caged birds, due          ple buy a chicken irrespective of its conforma-
to a greater maintenance requirement                tion or yield features. In these markets bird
because of higher activity levels and a greater     numbers are of greatest importance.
energy need for thermoregulation. This can              At time of writing some 85% of the chick-
range from 10% to 20% extra feed. Since             ens in the world are from one of four breeds.
feed represents about 65% of the cost of egg        All of these are heavy breeds, and are all very
production, this is a very significant increase.     similar in conformation. Their growth patterns
    Nutrient requirements of the modern             differ, as do their feed efficiencies and mortal-
layer have not changed significantly with time.      ity, but overall no one breed predominates.
While the egg mass output has increased dra-            Almost all of the worlds’ broiler chickens
matically, the feed efficiency has also              are kept in barns, where they can roam on the
improved, compensating for the extra output.        floor. However, as a consequence of appetite
Each breed company, of which there are              selection, the birds are not very active. Their
about ten major ones worldwide, produces its        average life expectancy is about 40 days, by
own tables of nutrient requirements for the         which time they will be expected to be in
particular strain but these hardly differ at all.   excess of 2.2 kg liveweight. To achieve this
    The most important aspect of commercial         weight they will have consumed about 3.75 kg
egg production is the rearing phase. If a pullet    of feed, depending on the feed cost per unit of
is grown to the right body weight (a guide to       energy, which equates to an FCR of 1.7.
its body composition) and stimulated into lay           Genetic improvement appears to progress
with an increasing-light pattern, its perfor-       unabated. Each year broiler weight at 42 days
mance can be predicted with a high degree of        increases by about 50 g, equivalent to achiev-
accuracy. Most problems experienced by the          ing the same body weight 1 day sooner each
industry are due to stimulating immature pul-       year. This saves maintenance, making the bird
lets that do not have the body reserves to cope     more feed efficient. It is also physiologically
with the stress of early lay. For the first few      younger, which means its growth is more effi-
weeks of lay the hen will be in a net energy        cient. The consequence of both these factors,
deficit, because her appetite is insufficient to      coupled with the intensive selection for feed
replenish her daily output of an egg. With          efficiency by appetite, means that FCR
time, nutrient intake from feed will exceed egg     improves by about 2 points per year as well.
mass output, on a daily basis, enabling the bird    As a consequence of these improvements, the
to regain lost body condition.                      nutrient requirements of the modern broiler
    The modern broiler chicken grew out of the      chicken are constantly changing. Trying to get
egg industry. Instead of destroying useless         the extra nutrients required for additional
males after hatching commercial layers, they        growth into a decreasing feed intake cannot
were reared for meat. Since the Second World        be balanced by the greater efficiency of the
War, as the demand for meat has increased,          birds, therefore the nutrient density of the
selective breeding for meat traits has taken        feed has to increase year on year.
place. Family selection for characteristics such        In an attempt to meet more accurately the
as weight for age, feed efficiency and carcass       bird’s nutrient requirement on any given day,
yield have led to the development of the            standard feeds (which were historically fed for
today’s meat breeds. Historically there were        10–14 days each) are now formulated as a
both heavy and light broiler breeder strains.       concentrate. They are then diluted with an
The heavy breeds were used by integrated            increasing daily percentage of whole wheat so
units, where one company owned the breed-           that the nutrient intake is different and exact
ing and broiler growing operations. In these        every day. The use of whole wheat as an on-
98                                           Chickpea




farm ingredient has the added benefit, over          Chinese         cabbage           Brassica     rapa
compound feed, of enabling development of           (Pekinensis and Chinensis group) is also
gizzard function. The feed is more effectively      known as celery cabbage, pak-choi, pe-tsai
ground and the pH rapidly lowered, immedi-          and wong bok. It has a mild flavour similar to
ately following ingestion. This has the effect      that of celery. Chinese cabbage is more closely
of reducing the bacterial load on the bird,         related to turnip and swede than to other vari-
thereby reducing mortality and morbidity,           eties of cabbage, its leaves being thinner and
leading to greater feed efficiency.        (KF)      more delicate than cabbage leaves. Cultivation
See also: Broiler chickens; Domestic fowl           practices are the same as for regular cabbage
                                                    but Chinese cabbage matures faster and may
Chickpea         A legume, Cicer ariatinum,         be ready in as little as 60–65 days after sow-
grown primarily for human consumption. The          ing. It is used fresh in salads or cooked like
seed varies considerably in colour (from black      regular cabbage and may become available for
to beige or white), shape and composition,          animal feed due to either oversupply or infe-
depending on the cultivar. Chickpeas have           rior quality. It is suitable for ruminants and can
been fed to pigs and poultry: they contain          be fed to dairy and beef cattle at 30% and to
about 200 g protein kg 1, about 300 g starch        ewes at 20% of their total diets. The dry mat-
kg 1 and about the same quantity of non-            ter (DM) content of Chinese cabbage is
starch polysaccharides. They contain small          90–110 g kg 1 and the nutrient composition
amounts of trypsin inhibitors. They also con-       (g kg 1 DM) is crude protein 210–230, crude
tain tannins, at low concentrations in the          fibre 100–120, ether extract 17–20, ash
light-coloured varieties; black cultivars contain   105–115 and neutral detergent fibre
about 2 g kg 1. Such low levels would be            275–285, with MER 11.5 MJ kg 1.              (JKM)
unlikely to cause detrimental effects in ani-
mals. The apparent metabolizable energy for         Chitin               A linear polysaccharide
poultry is about 12 MJ kg 1 and that for            chain of (1→4)-linked N-acetyl-D-glucosamine
ruminants about 14 MJ kg 1. Chickpeas are           (C8H13NO5)n units. It is the principal compo-
reported to contain phyto-oestrogens.        (TA)   nent of the exoskeleton of crustaceans (crabs,
                                                    lobsters, etc.), insects and spiders and is also
Chicory         A Mediterranean herb (Cicho-        found in some fungi, algae and yeasts. It is
rium intybus) of the family Asteraceae. It is a     similar in structure to cellulose but the C-2
hardy plant, the roots of which are used in         hydroxyl group is replaced with an acetylated
coffee substitutes and blends. The curled dan-      amino group. Upon acid hydrolysis, chitin
delion-like greens are used as potherbs, and        yields glucosamine and acetic acid. It is insolu-
true endive (C. endivia) is grown for salad.        ble in water, dilute acids or bases and is resis-
Forage chicory is grown in New Zealand and          tant to bacterial hydrolysis.              (TDC)
more recently in the USA for feeding to rumi-
nants. Forage chicory is a perennial plant,         Chitinase        An enzyme that liberates N-
producing leafy growth, which is higher in          acetyl-D-glucosamine from chitin. Chitinase is
nutrient and mineral contents than lucerne          produced in the gastric mucosa as well as by the
(alfalfa) or temperate grasses. Having a tap-       enteric microflora. An industrial preparation of
root it is drought tolerant but it can be dam-      chitinase     (chitodextrinase;   poly(1→4- -
aged by overgrazing and frost. Chicory              (2-acetamido-2-deoxy-D-glucoside))       glycan-
pastures have a lifespan of 5–7 years and           ohydrolase; EC 3.2.1.14) is purified from
yield 7.5–15 t ha 1 under rotational grazing,       Streptomyces griseus.                       (SB)
provided that they are maintained with a mini-
mum stubble height of 38–50 mm and given            Chitosan           Deacetylated chitin, i.e. a
rest periods of 25–30 days. The digestibility       polymer of D-glucosamine rather than of N-
of forage chicory leaves is 90–95% with a           acetyl-D-glucosamine. In feed ingredient analy-
protein level of between 100 and 320 g kg–1         sis, chitosan is classified as dietary fibre,
dry matter, depending on plant maturity.            isolated with the acid detergent fibre fraction.
                                         (JKM)      In the digesta it is positively charged and mim-
                                            Choice feeding                                           99




ics cholestryamine in sequestering cholesterol       nm. Both absorb essentially no light at      wave-
and other bile acids.                   (TDC)        lengths from 450 to 600 nm. Thus,            green
                                                     light passes through the tissue, giving      plants
Key reference                                        their characteristic colour.                 (NJB)
PDR for Nutritional Supplements (1st edn). Med-
  ical Economics Co. Inc., Thomson Healthcare,       Choice feeding              The provision of two
  Montvale, New Jersey, pp. 84–86.                   or more types of food, either simultaneously or
                                                     sequentially, can be made in order to deter-
Chlorella          A single-celled freshwater        mine feeding preferences or specific appetites,
blue alga, which ranges from 2 to 8 m in             or allow self-adjustment of nutrient intake to
diameter with an unusually high content of           meet specific requirements of individual ani-
chlorophyll. Chlorella completes its reproduc-       mals. If there is no nutritional advantage of one
tive cycle in 17–24 h and is rich in protein,        food over the other(s), the animal will prefer
vitamins, minerals and other bioactive sub-          that which has the more pleasant flavour. If one
stances including compounds referred to as           is toxic, then, no matter how initially pleasant
‘chlorella growth factor’. It is used as a feed      its taste, the animal will soon learn to avoid it in
for larval fish and in nutritional supplements        favour of a balanced food, even if that food has
for humans.                               (SPL)      a flavour that is initially unpleasant.
                                                         Pigs and chickens, when given a choice
Chloride          The ion of the inorganic ele-      between two foods, one containing more and
ment chlorine. It is required by living systems,     the other less of a nutrient than the optimum,
and in metabolism is usually found as a counter      will, within a few days, be choosing a mixture
anion to the cations sodium and potassium.           that provides a more-or-less balanced diet.
The distribution of chloride between extracellu-     This has been demonstrated for protein on
lar and intracellular fluid varies with the tissue.   numerous occasions and is also true for some
For example, the extracellular concentration         individual amino acids, minerals and vitamins.
relative to the intracellular concentration in       Such specific appetites depend on the animal
neurons is 13, in skeletal muscle 31, but in         learning to associate the sensory properties of
cerebrospinal fluid only 1.14. In regard to           each food with the metabolic consequences of
plasma osmotic pressure (290 mosm), chloride         eating that food; few, if any, specific appetites
is the major anion to counter sodium. The            are truly innate.
other significant anion is bicarbonate. In renal          Ruminants can also exhibit nutritionally
function, the reabsorption of sodium and chlo-       wise choice between high- and low-protein
ride plays a major role in body electrolyte and      foods, which is surprising in view of the fact
water metabolism. Laboratory animals fed chlo-       that the digesta from many meals are mixed
ride-deficient diets respond within hours by          together in the rumen and there is a long sep-
markedly reducing urinary excretion of chlo-         aration in time between eating a meal and
ride. Poor growth and reduced efficiency of           experiencing the metabolic consequences. It is
feed utilization (gain/feed) is seen within weeks    not yet clear the extent to which ruminants
of feeding a deficient diet. However, a chloride      are making selections for dietary nitrogen to
deficiency is not expected under normal feed-         support optimal rumen microbial activity, as
ing conditions.                             (NJB)    compared with selection to optimize the sup-
                                                     ply of amino acids to their own bodies.
Chlorophyll         A generic name applied to            Choice trials need to be designed carefully,
plant pigments involved in photosynthesis.           with adequate sample sizes, for the following
The chlorophylls trap light energy and direct it     reasons:
through chemical reactions to the production         1. Individual variation. Unless a preference
of ATP. Chlorophyll-a is a magnesium-con-            or avoidance is very marked (for example,
taining porphyrin and is the major chlorophyll       rejection of food or water tainted with a bitter
in algae and higher plants: it absorbs light at      substance such as quinine), there is great indi-
wavelengths from 400 to 450 nm and 640 to            vidual variation in preference. Hence, large
680 nm. Chlorophyll-b absorbs light at wave-         numbers of animals are needed to demon-
lengths from 430 to 500 nm and 640 to 700            strate a difference.
100                                       Choice feeding




2. Positional preference. Animals can learn        requirements for particular nutrients, based on
to associate differences in food composition       ‘specific appetites’ for those nutrients. Evi-
with the position in their pen of the food con-    dence for specific appetites can be obtained in
tainers. The position of foods offered should      a two-choice situation, either by offering the
be represented equally in all positions, and       nutrient concerned in one position and an
positions should not be switched for any par-      otherwise balanced diet that is lacking that
ticular animal even if the foods are easily dis-   nutrient in another position, or by offering
tinguished by other means, e.g. colour or          two versions of the same diet that are suffi-
flavour. To allow for social influences on           cient and deficient in the nutrient concerned.
choice, animals should be far enough apart         Alternatively, soluble nutrients can be pro-
for a neighbour’s presence not to interfere        vided in drinking water, and subjects eating a
with the subject’s choice.                         diet deficient in such a nutrient can be given a
3. Colour and flavour preference. An obvi-          choice between water with and without that
ous way to enhance a food’s identity is to         nutrient. Specific appetites may be in
flavour or colour it uniquely. Although some        response to a short-term demand, as for
animals have inherent flavour or colour pref-       example the demand for dietary calcium for
erences, these are easily overridden by the rel-   eggshell formation when an egg enters the
ative nutritional value of the foods. However,     shell gland of a laying hen. This has been
if the food preference itself is weak and if       demonstrated by offering hens a choice
novel flavours or colours are aversive to some      between a low-calcium diet and a separate cal-
animals (because of neophobia) more than           cium source such as oyster shell. Other spe-
others, it is important to use colours that are    cific appetites, however, may be in response
easily distinguished by the subjects, for which    to a long-term demand, as for example when
there are no marked preference or avoidance,       physiological requirements change prior to an
and to distribute the colours equally among        annual breeding season, or when an animal is
the foods being offered. Generally speaking,       suffering from a long-term deficiency in a par-
mammals learn to use food flavours more             ticular nutrient. Thus, some specific appetites
readily than colours as cues to nutritive value,   have been demonstrated experimentally by
while with birds the reverse is true.              feeding subjects on a diet deficient in the
4. Feeding preferences. Animals demon-             nutrient concerned for a week or so before
strate neophobia – a fear of new things – and      the choice trial. Most appetites are learned
this applies to foods. Preference or avoidance     and it may take many days for subjects to
of particular foods may be apparent in the         arrive at a balance between the foods on offer
short term, perhaps because of some novelty        that is sufficient to meet the requirement. In
effect, without being so in the longer term.       domestic fowls, specific appetites have been
Just because one food is eaten in greater          demonstrated for three minerals (calcium, zinc
quantities than the other does not mean that       and phosphorus), one vitamin (thiamine), pro-
the second is less palatable, simply that to       tein in general and two specific amino acids
make a balanced diet the animal should eat         (methionine and lysine). In addition, heat-
less of the second. The term ‘palatability’ is     stressed fowls have been shown to develop an
frequently, but wrongly, taken to be a prop-       apparent (learned) specific appetite for vita-
erty of a food, when in fact it is a property of   min C, which is known to alleviate the con-
the food, the animal, and the animal’s previ-      sequences of heat stress. In other words,
ous experience of eating this, or similar,         these birds learned that they felt better when
foods.                                             they ate more of the vitamin C-supplemented
                                                   food.
Specific appetites                                      Self-selection from compound feed and
Under natural conditions, herbivorous and          whole grain is increasingly allowed in com-
omnivorous animals usually select their (bal-      mercial poultry production. This saves money
anced) diets from potential food supplies that     by not having to mill the grain and assumes
vary greatly in terms of their nutritional con-    that an individual’s production of eggs or rate
tents. Such selection involves meeting specific     of growth is a cause, rather than a conse-
                                     Cholecalciferol derivatives                                101




quence, of its level of nutrient intake, and that   in serum calcium or a drop in serum phos-
birds are capable of adjusting their protein        phorus. The drop in serum calcium triggers
and energy intakes precisely to meet their          the parathyroid gland to secrete parathyroid
needs. In broilers, the proportion of whole         hormone that turns on the enzyme in the kid-
wheat in the diet is typically increased gradu-     ney to produce the active hormone from vita-
ally from 5% at 2 or 3 weeks of age to 20%          min D, i.e. 1 ,25-dihydroxycholecalciferol.
or more in the final week. All this wheat is         This major hormone causes the elevation of
eaten and it does not appear to cause greater       plasma calcium and phosphorus to normal
variation in body weight gain.                      levels that then suppress further production of
    For pigs and ruminants, studies of ability to   parathyroid hormone.
select a balanced diet have been largely con-           The daily requirement of cholecalciferol
fined to protein.                     (JSav, JMF)    for humans is 10 g or 400 IU. This amount
                                                    can be produced by 10 min of ultraviolet irra-
Cholecalciferol     A specific form of vita-         diation of hands and face by summer sunlight
min D, namely vitamin D3. This form of vita-        in northern hemispheres. A similar produc-
min D possess the cholesterol side-chain,           tion of vitamin D3 in farm animals can be
hence the prefix ‘chole’ on calciferol. It has       expected. However, in modern production
the structure:                                      methods, exposure to sunlight is limited and
                                                    supplementation is recommended. It is neces-
                                                    sary to supplement the diets of poultry with
                                                    10–20 g kg 1 of diet to prevent a defi-
                                                    ciency of vitamin D and supplementation of
                                                    diets for cattle, pigs and sheep is also recom-
                                                    mended.
                                                        Through its active hormonal form, vitamin
                                                    D has many functions beyond the elevation of
                                                    plasma calcium and phosphorus. It is believed
                                                    to function in the immune system, in the islet
    It is the form of vitamin D manufactured in     cells of the pancreas, in the parathyroid
skin by ultraviolet irradiation and is thus con-    glands to suppress the parathyroid gene, and
sidered the natural form of vitamin D. Chole-       parathyroid gland proliferation. It also is
calciferol is biologically inactive until it is     believed to function in the keratinocytes of
hydroxylated in the liver to 25-hydroxyvitamin      skin and should, therefore, be considered
D3, producing the blood form of vitamin D3.         more broadly than simply a substance that
This compound must then be further hydroxy-         prevents rickets in children and osteomalacia
lated in the 1 -position in the kidney to pro-      in the adult. A deficiency of vitamin D results
duce the final vitamin D hormone,                    in low plasma calcium and low plasma phos-
1 ,25-dihydroxycholecalciferol (trivial name:       phorus. In children it causes the disease rick-
calcitriol). This hormone derived from vitamin      ets, which is characterized by failure of
D stimulates the enterocytes of the small           calcification of the organic matrix of bone,
intestine to absorb calcium and phosphorus          resulting in deformities characteristic of the
into the plasma from the intestine. Together        disease. In adults, the deficiency disease is
with parathyroid hormone it causes the mobi-        called osteomalacia.                    (HFDeL)
lization of calcium from bone and together
with parathyroid hormone causes renal reab-         Cholecalciferol        derivatives       Com-
sorption of calcium in the distal tubules of the    pounds that possess the basic structure of vita-
kidney, resulting in a rise in serum calcium in     min D3 but have chemical modifications such
the blood to normal levels. Cholecalciferol,        as an acetate on carbon 3 (cholecalciferol 3-
therefore, is the building block from which the     acetate) or a hydroxyl group on the 25-carbon
vitamin D endocrine system is constructed.          (25-hydroxycholecalciferol) or a hydroxyl on
Production of the 1 ,25-dihydroxycholecalcif-       carbon 1 and a hydroxyl on carbon 25
erol in the kidney is dictated by either a drop     (1 ,25-dihydroxycholecalciferol). The acetate
102                                    Cholecystokinin (CCK)




increases lipid solubility and stability. The
                                                                            O
hydroxyl groups increase biological activity.
                                      (HFDeL)

Cholecystokinin (CCK)            A polypeptide                                                     O
hormone that stimulates enzyme secretion                                                    O
from the pancreas. CCK is produced in
endocrine cells in the small intestine, mainly
in the duodenum, where arriving peptides and                                     O
lipids stimulate its secretion into the blood,        O
which in turn stimulates the pancreatic secre-                                                  (NJB)
tion of proteases and lipases.            (SB)
                                                    Choline                         An organic base,
Cholesterol                      A neutral lipid,
                                                    (CH3)3·N+·CH2·COH. A major source of
C27H45OH, and the principal sterol of higher
                                                    choline is the phospholipid fraction of seed
animals. It is found in all body tissues, associ-
                                                    oils, eggs and animal fat. In metabolism it can
ated with lipids and membranes, in the
                                                    be directly incorporated into diacylglycerol to
plasma membrane as well as in intracellular
                                                    form phosphatidylcholine (lecithin) as cytidine
membranes such as those of the Golgi and
                                                    diphosphate choline. Phosphatidylcholine can
mitochondria of cells. It is synthesized in the
                                                    also be formed by methylation of phos-
body entirely from acetyl-CoA and is the pre-
                                                    phatidylethanolamine, three methyl groups
cursor of all other steroids in the body, e.g.
                                                    being added by S-adenosylmethionine. Phos-
corticosteroids, sex hormones, bile acids and
                                                    phatidylcholine is a critical constituent of cellu-
vitamin D. In the liver, cholesterol synthesis is
                                                    lar and subcellular membranes. When both
responsive to dietary cholesterol such that
                                                    fatty acids of phosphatidylcholine are palmitic
synthesis is decreased when dietary levels are
                                                    acid, it is a surfactant and plays an important
elevated. Cholesterol is in low-density (LDL),
                                                    role in the development of neonatal lung func-
intermediate-density, high-density (HDL) and
                                                    tion. As acetylcholine, it is involved in nerve
very low-density lipoprotein particles. It is
                                                    transmission. Choline can be oxidized to
delivered to tissues by LDL and removed from
                                                    betaine aldehyde and then to betaine and is
tissues by HDL. Cholesterol is excreted from
                                                    thus a source of the methyl group used in the
the liver in bile as cholesterol and as the bile
                                                    methylation of L-homocysteine to form L-
salts taurocholic acid and glycocholic acid.
                                                    methionine. The other two methyl carbons of
                                                    betaine become one-carbon sources (potential
                                                    methyl sources) via the folate system.      (NJB)

                              17                    Cholinergic mechanisms             The actions
                                                    of one portion of the autonomic nervous sys-
                                                    tem. Cholinergic neurons innervate sweat
                                                    glands, blood vessels and skeletal muscles.
                  H       H
          3                                         Stimulation of these nerves results in vasodila-
HO            5                                     tion. In general, cholinergic mechanisms are
      H           6                                 counteracted by the noradrenergic system
                                           (NJB)    which releases catecholamines.            (NJB)

Cholic acid            A primary bile acid,         Chondrocyte            A mature, differentiated
C24H40O5, usually conjugated with glycine or        chondroblast cell embedded in a cartilaginous
taurine. It is synthesized in the liver from cho-   matrix, similar to the osteocyte (mature
lesterol in a vitamin C-dependent step.             osteoblast cell). In the epiphyseal cartilage of
Because bile is usually alkaline, the carboxyl      growth plates, chondroblasts hypertrophy and
carbon is negatively charged and cholate is         calcify the matrix before apoptosis, reabsorp-
found in bile as the sodium or potassium salt.      tion and replacement by trabecular bone as a
                                            Chromatography                                           103




normal sequence of longitudinal bone growth           phases, a mobile and a stationary phase. All
by endochondral ossification. In articular carti-      separations involve the sample being trans-
lage, cartilage matrix is not calcified and chon-      ported in a mobile phase that may be a gas, liq-
drocytes maintain the extracellular matrix.           uid or supercritical fluid, through an immiscible
                                           (TDC)      stationary phase that is fixed in place in a col-
                                                      umn or on a solid surface. The phases are
Chopping            Forage ensiled in clamps,         selected so that components of the sample dis-
towers or ‘sausages’ is generally chopped prior       tribute themselves with repeated sorption/des-
to packing. Chopping increases the rate of            orption steps during the movement of the
release of cell nutrients, particularly water-solu-   analyte along the stationary phase. Those com-
ble carbohydrate: this stimulates the growth of       ponents that are retained strongly by the sta-
lactic acid bacteria and fuels the lactic acid fer-   tionary phase move slowly with the flow of the
mentation. It improves compaction, which, by          mobile phase, whereas weakly held compo-
excluding oxygen from the silo, increases the         nents travel rapidly. Due to these differences in
speed of fermentation and improves silage             mobility and distribution coefficients of the indi-
quality. Increased compaction also improves           vidual analytes in the sample, components sep-
the aerobic stability of silage at feed-out.          arate into discrete bands or zones that can be
     A range of forage harvesters have been           qualitatively or quantitatively analysed.
developed that chop forage to varying                     Chromatographic methods can be catego-
degrees. Flails harvest a standing crop or pre-       rized either by the physical means by which the
viously mown material with limited chopping;          phases come into contact, i.e. column chro-
forage is ensiled in long lengths. Machines that      matography in which the stationary phase is
harvest previously mown forage include: (i) the       held in a narrow tube, or by the types of
forage wagon, which has either no chopping            phases and kinds of equilibria involved in the
or a limited cutting action (forage is ensiled in     transfer of solutes between the phases. Three
long lengths); (ii) the double chop, which cuts       general categories of chromatography are liq-
each forage plant in two places (the forage is        uid chromatography (LC), gas chromatography
still ensiled in relatively long lengths but this     (GC) and supercritical-fluid chromatography
method is an improvement on the flail and the          (SFC), in which the mobile phases in the tech-
forage wagon); and (iii) the ‘precision’ chop or      niques are liquids, gases and supercritical fluids,
metered-feed, which can chop forage to                respectively. A detector placed at the end of
lengths of 25 mm or less, offering the opti-          the column can respond to an eluting analyte,
mum chop length for ensilage.                         and plotting of its signal as a function of time
     Traditionally balers did not carry out any       produces a series of peaks. The plot, known as
chopping of the forage. More modern balers            a chromatogram, can be used to identify com-
have double-cut or ‘opticut’ actions which            ponents of the sample based upon the position
enable limited chopping action for baled              of the peak or, from the area under the peak,
silage. Immediately prior to feeding, baled           give a quantitative measure of the amount of
silage can be chopped in bale choppers which          each component.
reduce the particle length to c. 50 mm. Such              In LC separations, normal-phase (NP) chro-
post-ensiling forage processing has shown             matography involves a polar stationary phase,
benefits in terms of forage digestibility and          such as silica gel or alumina, and a non-polar
intake and overall animal performance. (RJ)           mobile phase such as hexane, chloroform or
                                                      dichloromethane. It is used for the analysis of
Chromatography               A very powerful          relatively non-polar compounds; however,
method used in the separation of complex,             retention characteristics of silica gel are strongly
multicomponent samples and for the separa-            influenced by trace amounts of water. In
tion of an analyte from potential interferences.      reversed-phase (RP) chromatography, there is a
It includes a diverse and important group of          non-polar stationary phase and polar mobile
methods that permit the physical separation of        phase. It is ideal for the analysis of polar ana-
closely related components of complex mix-            lytes. HPLC (high-pressure liquid chromatogra-
tures. The components to be separated are             phy) is a variation of LC in which the mobile
selectively distributed between two immiscible        phase is forced along under high pressure to
104                                          Chromic oxide




allow for a greater efficiency of separation. If an    ommended intake for small laboratory animals
LC mobile phase consists of only one solvent          is between 1 and 2 mg kg 1 diet.      (PGR)
used for the analysis, the chromatography is
called isocratic. Alternatively, if the chromatog-    Further reading
raphy starts with one solvent or a mixture of         National Research Council (1997) The Role of
solvents and gradually changes to a different            Chromium in Animal Nutrition. National
                                                         Academy Press, Washington, DC.
mix of solvents as the analysis proceeds, it is
                                                      Stoecker, B. (1996) Chromium. In: Ziegler, E.E. and
said to be a gradient elution. Common LC
                                                         Filer, L.J. Jr (eds) Present Knowledge in Nutri-
applications include the analyses of substances          tion. ILSI Press, Washington, DC, pp. 344–352.
such as drugs, drug metabolites, antibiotics,
steroids, food additives, antioxidants, amino         Chromium picolinate            The chromium
acids, proteins, carbohydrates, lipids, pesticides,   (Cr) salt of picolinic acid. Chromium picoli-
herbicides, PCBs etc.                                 nate is one of many dietary Cr supplements.
    GC is used for the separation of volatile         Chromium appears to have a positive effect
components. For GC, the mobile phase (a               on insulin action and glucose metabolism.
gas) is usually helium or nitrogen but can also       Although positive effects have been reported
be hydrogen. Components of a mixture have             in diabetics, there do not seem to be anabolic
a different affinity for the stationary phase and      responses in animals.                   (NJB)
thus can be separated. Common GC applica-
tions include the analysis of hydrocarbons,           Key reference
PCBs, steroids, drugs, pesticides, fatty acids,       Lukaski, H.C. (1999) Chromium as a supplement.
amino acids, alcohols, ethers, chlorinated aro-          Annual Review of Nutrition 19, 279–302.
matics, glycols etc.                         (JEM)
                                                      Chylomicron            A lipoprotein particle
See also: Gas–liquid chromatography                   found in lymph and blood. It is made in the
                                                      intestinal cells from the hydrolysis products of
Chromic oxide             An inorganic com-           dietary triacylglycerols (fat), monoacylglycerols
pound, Cr2O3, which is not absorbed in the            and fatty acids, which are combined with a
digestive tract and is the marker most com-           protein. These particles are secreted into the
monly used in digestibility studies. However,         lymphatic system. The particles ultimately
its passage does not correspond well to that          enter the general circulation as chylomicrons.
of either the solid or liquid phase of the            Specific apolipoproteins bind to the chylomi-
digesta and it is therefore not a perfect             cron. Lipoprotein lipase in the inner wall of
marker. It may be used to mordant straw or            blood capillaries releases the fatty acids for tis-
cellulose: in this form it follows more closely       sue uptake.                                 (NJB)
the movement of solid digesta.             (SB)
                                                      Chyme        Intestinal contents, i.e. digesta,
Chromium            A transition metal (Cr) with      consisting of undigested food, endogenous
an atomic mass of 51.996. It exists in nature in      secretions, desquamated mucosal cells and
three oxidation states as +2, +3, or +6, with         microbes.                                  (SB)
+3 being the most stable. Chromium is pur-
ported to be involved in glucose metabolism in        Chymotrypsin                 The active form of
animals and humans through its influence on            chymotrypsin ( -chymotrypsin; EC 3.4.21.1)
insulin action. A Cr-containing oligopeptide          is an endopeptidase that hydrolyses primar-
that activates insulin receptor tyrosine kinase       ily those peptide bonds whose carbonyl
activity has been isolated from bovine liver. A       groups are contributed by aromatic amino
covalent complex of Cr and picolinic acid has         acids, i.e. tryptophan, phenylalanine or tyro-
been reported to enhance glucose tolerance            sine and, to a lesser extent, by leucine and
and insulin sensitivity in Type II diabetics. This    methionine. It is secreted from the pancreas
complex also has been shown to cause chro-            into the duodenum as its inactive precursor,
mosomal damage in Chinese hamster ovary               chymotrypsinogen, which is activated in the
cells. Although the US National Research              duodenum after excision of two internal
Council does not list recommended amounts of          dipeptides by trypsin.                     (SB)
Cr for any of the major farm species, the rec-        See also: Pancreatic juice
                                                Citrulline                                           105




Cimaterol            A phenethanolamine           2-   rhythm that oscillates every 24 h under a 24
adrenergic agonist (C12H18N3O, molecular               h light/dark cycle is a circadian oscillator –
weight 220). These compounds lack the cate-            only those that tend to persist under constant
chol nucleus of the catecholamines whose               conditions. It is likely that the activity of sero-
action they mimic and are therefore not sus-           tonin N-acetyltransferase, the main hormone
ceptible to degradation by the enzyme cate-            involved in the control of melatonin synthesis
chol-o-methyltransferase,        thus    exhibiting    in the pineal gland, is responsible for the reg-
prolonged action. Originally developed for use         ulation of circadian rhythms in birds, whilst a
as a bronchodilator in humans, but employed            circadian pacemaker in the suprachiasmatic
as a leanness-enhancing repartitioning agent           nucleus has been identified in mammals.
in livestock, cimaterol acts by redirecting                                                  (PDL, CLA)
nutrients from adipose tissue to skeletal mus-
cle. It is closely related to clenbuterol. (MMit)      Cirrhosis           A disease in which functional
See also: Beta agonists; Clenbuterol                   liver tissue is replaced by scar tissue (fibrosis).
                                                       Causes include alcoholism, infections (hepati-
Cinnamic        acid      C9H8O2,      molecular       tis), nutritional deficiencies (e.g. vitamin E,
weight 148. A phenylpropane derivative and the         selenium) and dietary hepatotoxins (e.g.
basic building block for many phenolic acids.          pyrrolizidine alkaloids). In advanced stages,
                                                       liver cirrhosis is irreversible.             (PC)

                                                       cis-Fatty acids         Unsaturated fatty acids
                                                       in which the double bonds are in the cis con-
                                                       figuration, making the carbon chain twist and
                                                       lowering the melting point. In the cis configu-
                                                       ration, the single hydrogens on the carbons of
   Cinnamic acid derivatives (phenolic acids)          the double bond are on the same side of the
occur in the cell walls of many forages and are        chain, whereas in the trans configuration they
involved in cross-linking fibre. The phenolic           are on opposite sides.                   (NJB)
acids are antimicrobials and hence may inhibit
digestibility of cell wall materials. The phenolic     Citric acid                           A six-carbon
compounds are metabolized by rumen                     tricarboxylic     acid,     molecular     structure
microbes and are conjugated with glycine as a          HOOC·CH2·C(OH)(COOH)·CH2·COOH. It is
mechanism of detoxification. Phenolic com-              produced in the mitochondrion by the combina-
pounds form complexes with proteins and                tion of oxaloacetic acid and acetyl-CoA pro-
other nutrients and therefore have antinutri-          duced in the catabolism of carbohydrates, fatty
tional activity, especially in animals on low          acids and some amino acids. This reaction
protein diets.                              (DRG)      forms part of the tricarboxylic acid cycle or
                                                       Krebs cycle. With the exception of erythrocytes,
Circadian rhythm             A circadian (circa,       citric acid is thought to be produced in all cells.
about; dies, a day) rhythm is a biological cycle       Citric acid can also leave the mitochondrion and
whose period length under constant condi-              provide the two-carbon acetyl-CoA units
tions (continuous illumination or total dark-          required for fatty acid biosynthesis.        (NJB)
ness, constant temperature and random
servicing and noise levels) is still close to,         Citrulline        An amino acid (C6H13N3O3,
though not necessarily equal to, 24 h. In poul-        molecular weight 175.2) not found in protein.
try, deep body temperature, locomotor activ-           It is a metabolite in the urea cycle that is syn-
ity and pre-ovulatory luteinizing hormone              thesized primarily in liver mitochondria from
release are examples of biological functions           carbamoyl phosphate and ornithine. Orally
that operate with a circadian rhythm. Under            ingested citrulline, either as free citrulline or
24 h conditions, most rhythms are principally          that in animal products, can be converted to
regulated by dawn, dusk or both signals, and           arginine in the kidney.                    (DHB)
oscillate at 24 h intervals. However, not every        See also: Non-protein amino acids; Urea cycle
106                                           Citrus products




Citrus products              Citrus pulp is the solid   chol nucleus of the catecholamines whose
residue remaining after the extraction of juice         action they mimic, and are therefore not sus-
or segments from citrus fruits. It typically repre-     ceptible to degradation by the enzyme cate-
sents 50–70% of the original fresh weight. It           chol-ortho-methyltransferase, thus exhibiting
comprises peel, rag (internal tissue) and seed in       prolonged action. Originally developed for use
proportions of approximately 60–65, 30–35               as a bronchodilator in humans but employed as
and 0–10%, respectively. The pulp, predomi-             a leanness-enhancing repartitioning agent in
nantly from oranges, is usually dried. Calcium          livestock, clenbuterol acts by redirecting nutri-
oxide, added to reduce the hydrophilic effect of        ents from adipose tissue to skeletal muscle. It is
the pectins, ensures that citrus pulp is a good         shown to promote growth and leanness in
source of calcium (2.2%); however, it is low in         broiler chickens, an effect that is markedly
phosphorus (0.2%). In composition and nutri-            influenced by dietary protein content. Clen-
tive value, citrus pulp is similar to sugarbeet         buterol is closely related to cimaterol.  (MMit)
pulp. Although the pectin and neutral deter-            See also: Beta agonists; Cimaterol
gent fibre contents comprise 50% of the pulp,
both are highly degradable. Protein and ash             Climate         Climate describes the usual
contents are low. Fresh pulp has a pH of 4.0            weather conditions of a location, whereas
but the buffering capacity is only one-fifth that        weather refers to the actual conditions (temper-
of grass silage. The pulp stores well in the            ature, humidity, wind, precipitation and baro-
absence of air and produces a high quality              metric pressure) at a given time. Both affect the
silage when combined with grass, the low pH             performance and productivity of animals in a
and residual sugars having an immediate                 variety of ways. Heat produced by metabolism
impact on the ensiling process. The pulp also           has to be dissipated to the environment as it is
has an absorptive action, restricting the loss of       produced, requiring a balance between heat
effluent and associated nutrients. To some               production and heat loss. Heat losses to the
extent the high fibre content limits its use in          environment can be influenced either reflexly
non-ruminants and if large quantities of seeds          or voluntarily by the animal, but only within
are present their limonin content could render          limits set by the physical laws that govern con-
the pulp toxic to non-ruminants.                        ductive, convective, radiative and evaporative
    Citrus molasses is the syrup produced by            exchanges, each of which is determined by cli-
concentration of the juice released from citrus         matic factors. Thus Newton’s Law of Cooling
peel. It has a typical dry matter content of 70%,       (a physical law) states that the rate of convec-
of which 60–65% is sugar, but is low in protein.        tive and radiative heat loss from a surface is
The material is highly viscous and requires to be       proportional to the temperature difference
stirred regularly. It is highly acceptable to cattle    between it and its surroundings; nothing the
but pigs require a few days to become accus-            animal does can alter this truism, but the slope
tomed to the flavour. In both cases it can               of the relationship (temperature difference per
replace up to 50% of the starchy concentrate in         unit heat loss, i.e. insulation) can be altered by
the diet of fattening animals.                 (FLM)    the animal. Dilation and contraction of periph-
                                                        eral blood vessels and erection of the hair or
Claws         Present in some animals and all           ruffling of the feathers are short-term reflex
birds, claws are formed from the terminal               actions that alter insulation; huddling and seek-
phalanges and are composed of closely                   ing shelter are voluntary short-term actions.
packed, renewable layers of keratinized cells           Long-term adaptations to climate include laying
producing horny pointed nails. In birds, claws          down of body fat and growth of the coat, both
are adapted for grasping, perching and preen-           of which increase insulation.
ing. In very young birds claws can be clipped               Evaporation from the body surface is pro-
to obtain blood samples.              (MMax)            portional to the vapour-pressure difference
                                                        between the surface and the surrounding air
Clenbuterol        A phenethanolamine    2-             (a physical law), the rate constant being
adrenergic agonist (C12H18Cl2N2O, molecular             dependent on the rate of air movement over
weight 277). These compounds lack the cate-             the surface. The animal can adjust the avail-
                                             Cobalamin                                            107




ability of moisture at the skin surface by          Clover silage          Two types of clover are
sweating and so increase the surface vapour-        commonly used in silage production: white
pressure, and it can increase air movement          (Trifolium repens) and red (Trifolium
over the respiratory passages by panting, but       pratense). Clover is usually ensiled as part of
no amount of reflex action by the animal can         a mixture with grasses. Clover contains low
overcome the final limit set by air humidity. If     concentrations of water-soluble carbohydrates
the absolute humidity of environmental air          but high concentrations of protein. The pro-
exceeds the saturation vapour pressure corre-       tein is of good feed value but its buffering
sponding to deep body temperature, evapora-         capacity makes the crop more difficult to
tive heat loss is impossible.                       ensile. This problem is exacerbated by the low
    Solar radiation can impose a large addi-        concentrations of water-soluble carbohydrate
tional heat load on an animal, even exceeding       available for lactic acid production during fer-
its normal rate of heat production. This is         mentation, thus an additive is essential. (DD)
beneficial in cold environments, but in hot cli-     See also: Silage
mates shade is essential to avoid it.
    At air temperatures below a certain level       Coating         Some feed materials may be
(the lower critical temperature), heat balance      coated to protect their chemical structure and
can only be maintained if the animal increases      hence nutritional value in extreme environ-
its heat production. This can be done reflexly       mental situations. For example, vitamin pre-
by shivering or voluntarily by exercise or by       mixes are normally coated with gelatin, which
increasing food consumption. Increased heat         minimizes the risk of the inherently unstable
production of stall-fed animals is wasteful if it   vitamins becoming denatured by heat during
involves extra feeding. So long as windbreaks       feed manufacture.
are available, the lower critical temperature is        Some feed ingredients may be protected to
unlikely to be reached by grazing mature            ensure maximum absorption in specific parts
sheep or cattle even in the very cold winter        of the gastrointestinal tract. This is particularly
conditions of North America, but their young        pertinent for ruminant animals, as many
require maternal warmth and protection.             materials are digested in the rumen and uti-
Deep snow is not of itself a serious cold haz-      lized by the resident microflora, the direct
ard for sheep, but proves fatal if it prevents      benefits to the host animal being lost. Pro-
them from finding food. Heavy rain reduces           teins, specific amino acids and fats may be
the coat insulation of many species, but does       treated in order to protect them from rumen
not penetrate the fleece of sheep.                   degradation so that they are absorbed in the
    At high air temperatures, an upper critical     abomasum or small intestine. It may be of
temperature is reached when an animal’s pro-        benefit to coat specific mineral elements with
ductivity falls. This is usually due to a reduc-    either a protein or a polypeptide to maximize
tion in food intake, either because herbage is      absorption. This is not only nutritionally valu-
sparse in hot climates or because the animal        able but also reduces environmental pollution
becomes unwilling to make the necessary             from the excretion of elements such as cop-
effort to find and eat enough food. This is          per.
particularly true of high-producing cows.               Pelleted compound feeds may be coated
                                        (JAMcL)     with flavours, medications or fats to improve
See also: Environmental temperature; Evapo-         palatability or for particular veterinary or
rative heat loss                                    nutritional reasons.                         (MG)

Cloaca         In birds and reptiles, the most      Cobalamin                          Vitamin B12,
posterior section of the alimentary canal, also     C63H88CoN14O14P, contains a corrin ring
receiving the terminal portions of the urinary      (similar to a porphyrin ring) with a cobalt ion
and reproductive ducts. In birds the cloaca is      at its centre. It is exclusively synthesized by
divided by folds of mucous membrane into            microorganisms and is not found in plants
three compartments: proctodeum, urodeum             unless they are contaminated by bacteria. In
and coprodeum.                          (MMax)      liver it is found as methylcobalamin, adenosyl-
108                                           Cobalt




cobalamin and hydroxycobalamin. It can be          factor in propionate metabolism. Propionate
provided as a vitamin as cyanocobalamin. In        can be produced from the catabolism of thre-
ruminants, B12 analogues are synthesized by        onine and methionine and from anaerobic
rumen microorganisms and a dietary supply is       intestinal fermentation. Propionate, as propi-
generally unnecessary. Cobalamin is absorbed       onyl-CoA, must be carboxylated by a biotin-
from the intestine by a complex system involv-     dependent       step    to   produce    methyl-
ing specific binding protein (intrinsic factor),    malonyl-CoA which, with the aid of the vita-
acid and proteolytic enzymes and is taken up       min B12 co-factor adenosylcobalamin, is ulti-
in the lower small intestine by specific trans-     mately converted to succinyl-CoA, which can
porters. In the blood it is transported by         be used in metabolism. A decrease in the par-
transcobalamine II. Once in the cell it can be     ticipation of B12 in this reaction leads to the
converted to methylcobalamin in the cyto-          urinary excretion of methylmalonate. Elevated
plasm. In this form cobalamin participates in      excretion of homocysteine and methyl-
a reaction in which L-homocysteine is methy-       malonate, while being signs of a deficiency of
lated by N-5-methyltetrahydrofolate to form L-     vitamin B12, can also be apparent in response
methionine and tetrahydrofolate. This is a         to a series of inherited disorders.
critical metabolic role for vitamin B12 in
methyl group and one-carbon metabolism. A                  N       O                          N
                                                                                      O                   N
deficiency of vitamin B12 results in a defi-
ciency of folate and elevated blood homocys-
teine. Animals deficient in vitamin B12 have                O                                                  O
elevated blood levels of homocysteine and ulti-
mately will show signs of a folic acid defi-        N                                  N
ciency. The reason for a folic acid                                     N                             N

involvement is that the release of tetrahydro-         O                        Co+
                                                               H
folate in the transmethylation reaction pro-                            N             N
vides tetrahydrofolate to be used in other         N
folate-dependent reactions.Without the trans-
methylation reaction, folate one-carbon units
are ‘trapped’ as N-5-methyltetrahydrofolate.
As the N-5-methyltetrahydrofolate pool builds              O

up, the tissue becomes deficient in tetrahydro-                                            O
                                                                                                  N
                                                                   N
folate and metabolic reactions requiring                                O
tetrahydrofolate as a co-factor slow or cease.
This limits the flow of one-carbon units from
                                                                   O–       O
serine, glycine, betaine, histidine, formate and           O
                                                               P
formaldehyde into the folate system. One                                              N
                                                           O       O
product excreted in the urine and representa-
tive of a folate deficiency is an intermediate in                                          N
                                                                            O
histidine catabolism, N-formiminoglutamate
(figlu). This limitation in one-carbon units                                                           (NJB)
decreases the ability of cells to produce
purines because fewer one-carbon units as N-       Key reference
10-formyltetrahydrofolate and N-5,N-10-            Seetharam, B. (1999) Receptor-mediated endocyto-
methenyltetrahydrofolate are available for the        sis of cobalamin (vitamin B12). Annual Review
nucleic acid (purine) synthesis. The result is a      of Nutrition 19, 173–195.
megaloblastic anaemia due to the impaired
DNA synthesis limiting cell division in the        Cobalt       A mineral element (Co) with an
developing erythrocytes. B12 is transported by     atomic mass of 58.93. It is an essential trace
transcobalamine II and once in a cell it can be    element for most animal species but, unlike
converted in the mitochondrion to adenosyl-        most other minerals, not in ionic form but as
cobalamin, which is required as a vitamin co-      a vital part of vitamin B12, or cobalamin,
                                               Coconut                                                     109




which is involved in methyl group transfer           main residue from processing, contain a toxic
reactions. A deficiency of the vitamin leads to       alkaloid, theobromine, which is poisonous to
anaemia. The minimal requirement of Co for           animals, but only traces of this are found in
ruminant animals is about 0.1 mg kg 1 diet           cocoa pods.
for sufficient microbial synthesis of vitamin            Although cocoa bean shells have a high
B12 for the animal to utilize. Cobalt itself is      protein level (16%; see table), the digestibility
non-toxic but 4–10 mg kg 1 body weight               of the protein is low (6.6%). Cocoa pods can
could cause loss of appetite and reduced             be used in a maintenance ration for small
weight gain. Ionic Co is readily absorbed from       ruminants, comprising up to 25% of the diet.
the gut and shares a common pathway with             Up to 7 kg day 1 has been fed to dairy cattle
iron. Co is excreted primarily in the urine.         without adverse effects. Dried and ground
                                          (PGR)      pods can be included in concentrate mixtures
                                                     at up to 20% without deleterious effects on
                                                     production levels.                         (LR)
Further reading
Smith, R.M. (1987) Cobalt. In: Mertz, W. (ed.)       Nutrient composition (% dry matter).
   Trace Elements in Human and Animal Nutri-
   tion, 5th edn. Academic Press, Harcourt Brace                               CP     CF    Ash    EE     NFE
   Jovanovich, New York, pp. 143–183.                Cocoa pods                7.8 35.1 10.4       2.3   47.6
Stabler, S.P. (2001) Vitamin B-12. In: Bowman,       Cocoa bean shells        16.0 17.4 10.8       3.2
   B.A. and Russell, R.M. (eds) Present Knowl-
   edge in Nutrition. ILSI Press, Washington, DC,    CF, crude fibre; CP, crude protein; EE, ether extract; NFE,
   pp. 230–240.                                      nitrogen-free extract.

Coccidiosis          Parasitism by protozoa of
                                                     Further reading
the genera Eimeria, Isospora, Cystoisospora
                                                     Devendra, C. (1988) Non-conventional Feed
or Cryptosporidu. Nearly all animals are sus-           Resources      and     Fibrous     Agricultural
ceptible. Infection generally results in the inva-      Resources. IDRC/Indian Council for Agricul-
sion and destruction of the intestinal mucosa           tural Research, Ottawa, Canada.
with subsequent diarrhoea and productive             Gohl, B. (1981) Tropical Feeds. FAO Animal Pro-
losses. Severity of the disease is directly             duction and Health Series, No. 12. FAO, Rome.
related to the dose (number of oocysts
ingested) and the immune and nutritional sta-        Coconut (Cocos nucifera L.)                Nuts
tus of the host. Both improved management            are produced on the coconut palm tree,
to prevent oral exposure to infective oocysts        which can grow in poor sandy conditions.
and treatment with coccidiostats are effective       The nut consists of a hard shell covered by a
in control.                                 (BLS)    fibrous outer layer, with an edible kernel
                                                     inside. The nut must be split and the kernel
Cockerel             A young male domestic           dried for storage. Coconut water contained
fowl. Mature birds are described as cocks or         inside the nut is usually discarded. Oil can be
roosters.                           (KJMcC)          extracted from copra, the dried kernel. The
                                                     fibrous outer layer has no feed value. Rumi-
Cocoa bean (Theobroma cacao L.)                      nants can graze coconut orchards once the
The cocoa tree is indigenous to South Amer-          trees have reached 5–6 years old.
ica, but the main centre for cocoa bean pro-             Copra is too valuable to use as a livestock
duction is tropical West Africa. Cocoa beans         feed, but coconut meal (the residue after oil
are found in large yellow or orange pods             has been extracted) is used as an animal feed.
which grow directly on the stems or branches         The oil content of coconut meal varies widely
of the tree. Beans are removed from the pod          according to the efficiency of the extraction
and fermented with its encasing white                method. Coconut meal is rich in energy and
mucilage, and dried for processing into cocoa        protein (Table 1) and can be used for lactating
powder and cocoa oil. Pods contain a high            animals. It becomes rancid as it ages, as a
concentration of potassium. Cocoa shells, the        result of oxidation of residual oil, and can
110                                                       Cod




Table 1. Typical composition of coconut products (% dry matter).

                               DM(%)          CP          CF         Ash            EE     NFE        Ca      P

Coconut meal,
     mechanical extraction       88.7        19.5        8.5         5.4            18.4   48.2
Coconut meal,
     solvent extraction          93.4        20.5        26.1        7.0             0.4   46.0
Coconut meal, expeller           88.8        25.2        10.8        6.0             5.2   52.8       0.08   0.67
Copra                            50.0         9.7         4.3        2.9            64.4   18.7       0.03   0.26

CF, crude fibre; CP, crude protein; EE, ether extract; NFE, nitrogen-free extract.


            Table 2. Digestibility (%) and ME content of coconut meal.

                                              CP          CF          EE            NFE    ME (MJ kg 1)

            Ruminant
                 Coconut meal,
                      expeller               91.0        35.0        95.0           80.0      13.16
            Pigs
                 Coconut meal,
                      expeller               70.0                                             13.08




cause diarrhoea. The meal is low in lysine,                     Cod, haddock and pollock belong to the Gadi-
isoleucine and methionine but has a high fibre                   dae, a family of physoclistous, soft-rayed
content (Table 2). The maximum safe amount                      fishes featuring thoracic pelvic fins and, fre-
in dairy cow rations is < 2 kg day 1 because it                 quently, a barbel on the lower jaw. The aqua-
leads to a harder butterfat. Beef cattle can                    culture production cost of cod is relatively
consume higher levels without adversely                         high due to slow growth and early sexual mat-
affecting carcass fat. Coconut meal should be                   uration problems, which may be reduced by
introduced gradually into livestock rations.                    photoperiod manipulation.
    Because livestock can eat young coconut                         There is small-scale cod hatchery produc-
leaves, which damages tree development,                         tion and grow-out in Newfoundland and,
grazing in coconut plantations is restricted                    more recently, the New England states have
until trees are too high for the animals to                     initiated a successful early rearing pro-
reach the leaves.                            (LR)               gramme. Atlantic cod eggs are buoyant,
                                                                1.2–1.6 mm in diameter and have no oil glob-
                                                                ule. Hatching occurs in 14–40 days at 6 and
Further reading                                                 0°C, respectively. Newly hatched larvae are
Devendra, C. (1988) Non-conventional Feed
                                                                4.0–4.5 mm long and are pelagic until a
   Resources      and     Fibrous     Agricultural
   Resources. IDRC/Indian Council for Agricul-
                                                                length of 25–50 mm. Larvae can be success-
   tural Research, Ottawa, Canada.                              fully reared to metamorphosis on a sequential
Gohl, B. (1981) Tropical Feeds. FAO Animal Pro-                 diet of microalgae, live food organisms such
   duction and Health Series, No. 12. FAO, Rome.                as rotifers and artemia, and microparticulate
                                                                weaning feeds.                         (RHP)
Cod         Atlantic cod (Gadus morhua, L.)
occurs naturally on both sides of the North                     Cod liver oil          Oil obtained from the liv-
Atlantic from Iceland and Spitsbergen to the                    ers of cod and other fish from the Gadidae
Baltic Sea and Bay of Biscay in the eastern                     family. It is used as a source of unsaturated
Atlantic, and from Greenland to Cape Hat-                       fatty acids (oleic, docosahexaenoic and eicosa-
teras, North Carolina, in the western Atlantic.                 pentanoic) and fat-soluble vitamins. The nutri-
                                                      Cold environment                                          111




ent composition is 38 MJ energy kg 1,                                   Coffee meal is a dark brown to black
1,000,000 IU vitamin A and 100,000 IU                               residue produced when coffee seeds are
vitamin D kg 1, with 226 g saturated, 467 g                         removed from the outer coating, dried and
monounsaturated and 225 g polyunsaturated                           then roasted. Coffee meal is high in fibre and
fatty acids kg 1 and 5700 mg cholesterol                            has a very low energy value. It is a bitter prod-
kg 1.                                 (JKM)                         uct that inhibits food intake and will reduce
                                                                    overall feed intake if fed at levels greater than
Coenzymes          Metabolically   essential                        2–4% of the total diet. It has a strong diuretic
compounds derived from B vitamins. The                              effect, which encourages urinary nitrogen and
vitamins themselves are not able to partici-                        sodium losses, making it unsuitable for feeding
pate as enzyme co-factors in metabolism.                            to horses. Coffee meal can contain high oil
For example, thiamine is metabolically con-                         levels which interfere with fibre digestion in
verted to its mono-, di- and triphosphate                           ruminants at high inclusion levels. In addition,
forms. It functions as a vitamin co-factor                          the oil content may cause the product to
only as thiamine diphosphate.         (NJB)                         become rancid in storage. Coffee meal can be
                                                                    fed to dairy cows, beef cows and ewes, but
Coffee        Coffee production for human                           not at an inclusion level greater than 4%.
consumption gives rise to a number of by-                               Dried coffee leaves have a relatively low
products that may be used as ruminant feeds.                        nutritional quality but they can be included in
These include leaves, pulp from the bean, cof-                      concentrates. The high tannin content of the
fee residues, coffee meal and spent coffee                          coffee leaves reduces the digestibility of pro-
grounds. The fresh fruit consists of 45% pulp,                      teins and possibly of other dietary compo-
10% mucilage, 5% skin and 40% bean. To                              nents. Spent coffee grounds, or cherko, are
produce coffee the fruit is processed to free                       the waste product from instant coffee produc-
the bean from the pulp, which accumulates in                        tion. These are unpalatable and contain
large quantities and is used in some areas as                       diuretics including caffeine, and tannins that
roughage for cattle. The fruit can be                               reduce protein digestibility; inclusion rates
processed by either a dry method or by a wet                        should not exceed 2.5%. The nutritional com-
soaking method. The pulp from the dry                               position of spent coffee grounds can be
method is fibrous and rather poor roughage                           improved by solid fermentation (see Solid-
(see table), whereas that from wet processing                       state fermentation).                       (JKM)
has much greater feed value. Coffee pulp
from the wet method can be fed to lactating                         Cold environment           In a cold environ-
dairy cattle at levels below 20% of the diet                        ment an animal is forced to raise its metabo-
without affecting milk production. Digestibil-                      lism above the normal level in order to keep
ity of pulp (dry method) in sheep is crude                          warm. This occurs at the so-called lower criti-
protein 10.3%, crude fibre 27.9%, ether                              cal temperature, which in still air can be as
extract 53.2% and NFE 50.2%, with ME                                low as –40°C for a fully fleeced sheep and as
1.33 MJ kg 1.                                                       high as 34°C for a newly hatched chicken.

Typical composition of coffee products (g kg     1   dry matter).

                                  Dry matter
                                   (g kg 1)            Crude protein        Crude fibre      Ash       EE        NFE

Dried leaves                          936                    99                187          130        59       525
Residue/meal                          910                   120                440           17        25       398
Pulp, wet method                      230                   128                241           95        28       508
Pulp, dry method                      900                    97                326           73        18       486
Skins, Columbia                       900                    24                952            4         6       214
Coffee ground                         197                   133                624            5       196        42
Coffee oil meal                       898                   174                270           55        18       483

EE, ether extract; NFE, nitrogen-free extract.
112                                         Colestyramine




Wind causes a decrease and solar radiation an        gen type 1 are made of approximately 1000
increase in the critical temperature. (JAMcL)        amino acids. The three polypeptide chains have
See also: Climate; Environmental temperature         a unique amino acid sequence. A structural
                                                     requirement for the triple helix assembly is a
Colestyramine          A synthetic strong            glycine residue in every third amino acid posi-
basic anion-exchange resin. It has quaternary        tion. Two other amino acids found in high fre-
ammonium functional groups attached to a             quency are proline and hydroxyproline.
polystyrene polymer. It can bind bile salts and      Hydroxyproline is formed by post-translational
if consumed in sufficient amounts may alter           modification of proline during collagen synthe-
the excretion of cholesterol-based substances.       sis. Hydroxyproline accounts for 13–14% of the
                                          (NJB)      total amino acid content of collagen. These two
                                                     amino acids make the structure more rigid.
Colic        Severe and sudden attack of             Another structurally important amino acid found
abdominal pain, often caused by indigestion.         in collagen fibrils is lysine. A post-translational
Caused in horses by the presence of gas,             modification of the -amino group of lysine
impaction of the colon, or a variety of other        involves conversion to a hydroxyl group to form
gastrointestinal disorders. It may also be           hydroxylysine. Hydroxylysine can bind cova-
caused by large numbers of parasitic worms,          lently to hydroxylysine in adjoining polypeptide
urinary calculi or nephritis.           (JMF)        chains to form cross-links, making a more rigid
                                                     structure. The enzymes involved in forming
Colitis       Inflammation of the colon, often        hydroxyproline (prolyl hydroxylase) and hydroxy-
accompanied by haemorrhage and ulceration.           lysine (lysyl hydroxylase) both require ascorbic
Symptoms are abdominal pain, fever, watery           acid (vitamin C) as a co-factor. This requirement
diarrhoea, dehydration, hypovolaemia, tox-           may explain the bleeding gums and poor wound
aemia, leucopenia, decreased serum Cl, Na            healing seen in scurvy (vitamin C deficiency) in
and K levels and metabolic acidosis. The dis-        humans, other primates and some birds.
turbances of mineral balance arise from dam-             As a nutrient source, collagen is an incom-
age to the epithelial tissue of the colon. The       plete protein with regard to the amino acid pat-
aetiological agents are many and include             tern required by simple-stomached animals, as
Escherichia coli, Salmonella spp., Clostrid-         it is devoid of the indispensable amino acid
ium spp., Ehrlichia risticii, Cyathostomes,          tryptophan. Collagen has less than one-half the
fungi, various antibiotics, drugs and toxins. All    required concentrations (1 g amino acid 16 g 1
farm animal species are potentially affected         nitrogen) of eight of the nine indispensable
and can transmit the infection to humans.            amino acids; it also has excessive concentra-
                                         (CJCP)      tions of the dispensable amino acids glycine,
                                                     proline and hydroxyproline, which make up
Collagen           A fibrous protein that makes       47% of the total amino acids. Hydroxyproline
up the major portion of white fibres in connec-       cannot be used as an amino acid in protein
tive tissues. It is found in skin, tendons and       synthesis, as it is only produced from proline
bones and contributes approximately 25% of           during collagen synthesis.                  (TDC)
body protein in mammals. Collagen is con-
verted to gelatin by boiling in water. At least 19   Colon        That part of the digestive tract
types of collagen, at least 35 mammalian colla-      that lies between the caecum and the rectum
gen genes and at least 30 separate polypeptide       (or, in those species lacking a caecum,
chains have been identified. The characteristic       between the ileum and the rectum). The colon
molecular structure of collagen can be described     is the main site for the resorption of water
as a three-stranded rope with strands winding        and sodium. It is also important for microbial
around each other with a 1.5 nm right-handed         activity and production of short-chain fatty
twist. The polypeptide chains that make each         acids (SCFA), particularly in non-ruminant
strand have a left-handed twist composed of 18       herbivores, such as the horse, in which up to
amino acid residues for each turn in the helix.      70% of absorbed energy is from SCFA pro-
The three polypeptide chains of mature colla-        duced in the colon.                       (SB)
                                           Common carp                                           113




Colonization: see Gastrointestinal microflora;       blood of the neonate but remains in the gut to
Rumen microorganisms                                act to protect the gut wall against infection.
                                                        Immunoglobulin G (IgG) is transported and
Colostomy          Surgical removal of the          concentrated from the dam’s sera into
large intestine with the creation of a fistula for   colostrum by mammary acinar cells. Thus if cir-
the outlet of digesta from the distal ileum.        culating IgG is present at a high concentration
                                             (SB)   in response to a specific antigen in the dam’s
See also: Cannula                                   sera, it should also be at a high concentration in
                                                    the colostrum. This type of antibody is specifi-
Colostral     immunity         This    passive      cally transported across the neonate’s intestinal
immunity is of potentially enormous benefit to       epithelium (optimally in the lower jejunum in the
the young animal. It can provide protection         calf) and into the circulation, provided that the
against species-specific and environmental           neonate is less than 36 h old. Absorption of
pathogens to which the dam, or colostrum            antibody is reduced after the neonate is 12 h
provider, was exposed before parturition. This      old. Unless infected as a fetus, neonates of most
passive protection may be systemic, from            farm species are born without gamma globulins
colostral antibodies absorbed in the first           in their circulation. Measurement of serum IgG
24–48 h of life, or by local action in the gut      in the neonate can thus indicate whether a satis-
subsequent to this.                       (EM)      factory amount of colostrum has been con-
See also: Immunity                                  sumed and antibody absorbed. Calves with less
                                                    than 10 mg IgG1 ml 1 are considered
Colostrum          The milk formed before           hypogammaglobulinaemic.
and around the time of parturition. It may dif-         It is generally accepted the neonate should
fer in consistency (thicker) and colour             consume 10% of its body weight in colostrum
(cream/beige/yellow) from subsequent milk           in the first 24 h and if possible half of that in
production.                                         the first 6 h of life. Colostrum contains trypsin
    Colostrum is the major source of passive        inhibitors to help to prevent breakdown of the
immunity for most domestic animals (in con-         antibody proteins. Antimicrobial factors such
trast to humans, rabbits and guinea pigs) and is    as lysosomes, lactoperoxidases and lactofer-
also a rich source of nutrients. Lipids and pro-    rins are also present.
teins (primarily caseins and albumins) are pre-         Antibody levels in colostrum drop rapidly
sent in relatively high concentration, around       over the first few days of lactation. By day 3,
20%, but lactose levels are lower than in sub-      globulin levels are less than 10% of those in
sequent milk production. Vitamin content is         the first colostrums to be produced.
high, particularly vitamin A, which is impor-           If the dam has no colostrum, donor
tant in pigs and calves as placental transfer is    colostrum or frozen stored colostrum can be
limited. Colostrum acts as a natural laxative in    used. Commercial colostrum substitutes are
the neonate, aiding passage of the meconium,        also available.                              (EM)
the accumulated fetal faecal material.              See also: Immunity
    Immunoglobulins in colostrum protect the
neonates in two ways. IgA acts locally in the       Common carp (Cyprinus carpio)                 A
gut lumen and IgG is absorbed into the              freshwater fish of the family Cyprinidae, prob-
neonate’s circulation, providing short- to          ably the most abundant domesticated fish
medium-term protection to specific diseases.         species. It has four subspecies: C. c. carpio of
In many mammals IgG is the major                    the European–Transcaucasian area; C. c.
immunoglobulin in colostrum, though IgA is          aralensis of the mid-Asian region; C. c.
present in milk for longer.                         haematopterus of the Amur–Chinese or Far
    Immunoglobulin A (IgA) is produced in the       Eastern region; and C. c. viridivio-laceus of
mammary gland by plasma cells that have             North Vietnam; and a large number of strains
migrated from gut-associated lymphoid tissue        are known. The original natural distribution of
of the dam, where they are stimulated by the        common carp was probably restricted to a
gut flora. This IgA is not absorbed into the         narrow belt in central Asia but it has been
114                                     Comparative slaughter




introduced into so many parts of the world           nants fed on low-quality conserved roughage
that it now enjoys the status of a virtually         are turned out to fresh grass in the spring or
global fish and its culture is very widespread.       when the poor forage of a dry season is
Common carp are omnivorous fish and can               replaced by lush growth when the rains return.
be polycultured with other freshwater species.           Undernutrition may be either quantita-
Carp dig and burrow into pond embankments            tive, with less feed consumed per unit of time,
and sides in search of organic matter. They          or qualitative, with reduced concentrations of
gulp in mud, from which digestible matter is         usable energy or specific nutrients in the diet.
sieved and the rest rejected – a habit that          The extent to which compensatory growth
often makes pondwater turbid. In the wild,           occurs depends on the severity of the under-
adult common carp thrive on decayed veg-             nutrition, the stage of growth during which it
etable matter containing bottom-dwelling             is imposed and the length of time for which
organisms, notably tubificids, molluscs, chi-         undernutrition continues.
ronomids, etc. In some countries the common              The precise scientific explanation of com-
carp is considered a nuisance species.               pensatory growth is fraught with many difficul-
    Although common carp have been farmed            ties. Experiments purporting to demonstrate
since ancient times, scientific studies of their      compensatory growth require great clarity of
nutrition is of relatively recent origin (mid        thought for proper elucidation. The growth
1960s) and most of the work is conducted on          rates of all animals slow down as they
small fish under laboratory conditions and on         approach maturity, so when they are com-
post-juvenile stages in net-cage culture with        pared with ones that are physiologically
practical diets. The protein requirement is          younger, the latter will appear to be growing
30–38% crude protein in the diet. Common             more rapidly. Compensatory growth in some
carp can effectively utilize both carbohydrate       circumstances may merely be a reflection of a
and lipid as dietary energy sources. For growth      rehabilitated animal rejoining its normal
of carp, the optimum ratio of digestible protein     growth curve at a younger physiological age
(mg) to energy (kcal) is 97:116. Common carp         than its contemporaries. For this reason it is
have no stomach and it is better to feed them        helpful to compare animals of similar physio-
frequently, about four times a day.       (RMG)      logical age (or weight range) rather than those
                                                     of similar chronological age.
Comparative slaughter              The sacrifice          Many publications refer only to an acceler-
of research animals for the purpose of measur-       ation of observed liveweight gain. This does
ing changes in the composition of the whole          not allow a distinction to be made between
body or in the mass or composition of a tissue.      the growth of bone and muscle and the rela-
The whole animal or the part of interest may         tively simple changes resulting from a sudden
be analysed for some biochemical or chemical         increase in gut-fill (very significant in rumi-
analyte. Animals in an initial control group are     nants) or the rapid responses of the accessory
slaughtered at the beginning of the experiment       organs of digestion such as the intestines and
to provide a baseline against which changes          liver. Only in experiments where there has
can be assessed.                           (JSA)     been a degree of carcass evaluation or mea-
                                                     surement of chemical changes can tissue dif-
Compensatory growth               The accelerated    ferences be confidently affirmed.
growth that occurs when previously undernour-            Apparent changes in efficiency have been
ished animals are well fed. They then appear to      variously explained as a carry-over of adaptive
grow faster and more efficiently than similar ani-    responses to undernutrition, including a
mals that have been continuously fed. Compen-        reduced maintenance requirement and
satory growth occurs in ruminants and                reduced energy costs of tissue deposition.
non-ruminants. It is sometimes referred to as        Early feed restriction in broilers has been
‘catch-up growth’, particularly in humans where      shown to reduce abdominal fat but not overall
it can be observed after a period of prolonged       body weight, leading to an improvement in
infection and poor food intake. In the agricul-      efficiency. This has been attributed to
tural context, it is characteristically associated   impaired hyperplasia of adipocytes in the
with the spurt of growth that occurs when rumi-      restricted groups.
                                             Complementation                                           115




    Many experiments show an enhanced daily              Blaxter, K.L. (1989) Energy Metabolism in Ani-
intake per kilogram body weight in the compen-              mals and Man. Cambridge University Press,
sating group, as for example in pigs (Ratcliffe             Cambridge, UK.
and Fowler, 1980). Another key feature of the            Lawrence, T.L.J. and Fowler, V.R. (2002) Growth
                                                            of Farm Animals, 2nd edn. CAB International,
apparent improvement in efficiency is due to tis-
                                                            Wallingford, UK.
sues with a relatively low energy density being
                                                         Ratcliffe, B. and Fowler, V.R. (1980) The effect of
deposited in the gain of the compensating                   low birth weight and early undernutrition on
group. This is due to a preferential growth of              subsequent development in pigs. Animal Pro-
muscles and organs rather than the growth of                duction 30, 470 (abstract).
adipose tissues (Blaxter, 1989; Lawrence and
Fowler, 2002). In many agricultural situations,          Competition           Animals in a group may
compensatory growth is a corollary of circum-            compete with each other for access to food or
stances in which the growth curve is necessarily         water when availability of these resources is
interrupted by a seasonal food shortage. Exam-           limiting relative to demand. This can occur if
ples of deliberate exploitation of the phenome-          there is insufficient space at feeders or drinkers
non are rare, although Auckland et al. (1969)            (especially nipples), or if the food or water sup-
claimed that a ‘low–high’ pattern of protein             ply is intermittent. Demand for food is greatest
concentration in the diet gave a greater                 when animals are subjected to restricted feed-
efficiency of protein utilization in turkeys than         ing programmes, and demand for water
did feeding them continuously with a high con-           increases when ambient temperature rises.
centration. Deliberately slowing growth may be           Animals in a group tend to feed and drink syn-
of benefit in the context of metabolic diseases           chronously, due to social facilitation, and com-
such as ascites and bone disorders in poultry            petition at feeders and drinkers can lead to
and this may be more acceptable if the period            aggression, fights and injury, as dominant ani-
of retardation is followed by a period of com-           mals displace subordinate ones.             (JSav)
pensatory growth.                          (VRF)
                                                         Complementation            The positive result
Key references                                           of mixing one or more proteins to achieve a
Auckland, J.N., Morris, T.R. and Jennings, R.C.          more favourable dietary amino acid pattern.
   (1969) Compensatory growth after undernutri-          When the amino acid pattern of one protein or
   tion in market turkeys. British Poultry Science       mixture of proteins provides amino acids that
   10, 293–302.                                          are limiting in the pattern of another protein,




Animals in a group compete for access to food if there is insufficient space at feeders.
116                                         Complete feed




the process of mixing the proteins in a specified     ease of handling and use on farms. The
ratio yields a mixture of amino acids that meet      energy content of pelleted compound feeds is
the animal’s needs for a specific process (e.g.       often increased by spraying oil on to the pel-
growth, milk production) at a lower total nitro-     lets during the final phase of manufacture.
gen intake. Thus, the amino acid pattern of one      Compound feeds are colloquially referred to
protein complements that of another.       (NJB)     as concentrates.                        (PCG)

Complete feed            A mixture of dietary        Computed tomography (CT)                   Also
ingredients designed to meet all the nutrient        called computed axial tomography (CAT), a
requirements of an animal. The mixture is            specialized form of X-ray technique that
normally mixed to a uniform blend so that the        acquires cross-sectional images of the body.
animal cannot select individual ingredients.         The X-ray source and scanner rotate around
    For pigs and poultry, complete feeds are         the body measuring the transmission of the X-
usually blended from cereals and protein             ray beam from which cross-sectional images
sources, with added oil, minerals and vitamins       are generated by computer. The image has
to meet requirements. For ruminants, complete        dark and light areas corresponding to specific
feeds (often referred to as total mixed rations)     tissues. Computed tomography is used in ani-
contain a mixture of forages, by-products, cere-     mal nutrition studies to detect and measure
als, protein sources, fats, minerals and vitamins.   adipose tissue, muscle and bone. CAT scan-
    Complete feeds are normally designed to be       ning is widely used in clinical practice. (SPL)
fed ad libitum, which requires an estimation of
potential voluntary feed intake. Where less pro-     Computer software               Programs, or
ductive stock are offered complete feeds (e.g.       series of instructions, performed by a com-
sows in early pregnancy), the metabolizable          puter to fulfil a task or application. For exam-
energy content of the complete feed is nor-          ple, a word processor, database, spreadsheet
mally reduced, by inclusion of high-fibre             or feed formulation utility.               (RG)
sources, so as to limit energy intake and pre-
vent excessive deposition of body fat. In rumi-      Key references
nants, voluntary feed intake is usually greater      Baber, R.L. (1987) The Spine of Software:
when forages and concentrates are mixed as a            Designing Provably Correct Software: Theory
complete feed than when offered separately.             and Practice, or, a Mathematical Introduction
                                                        to the Semantics of Computer Programs.
This is because the microbial population of the
                                                        John Wiley & Sons, Chichester, UK.
rumen reaches a stable equilibrium that
                                                     Beck, L.L. (1985) Systems Software: an Introduc-
enhances the digestibility of the forage compo-         tion to Systems Programming. Addison-Wes-
nents. Complete feeds also allow utilization of         ley, Reading, Massachusetts.
less-palatable feed ingredients that would other-    Geisler, P.A. and France, J. (1981) Computers and
wise be rejected when fed separately.        (PCG)      their potential: software. In: Hilyer, G.M., Whit-
                                                        temore, C.T. and Gunn, R.G. (eds) Computers
Composition: see Body composition; Botan-               in Animal Production. Occasional Publication
ical composition; Chemical composition; Feed            No. 5, British Society of Animal Production,
composition; Meat composition                           Edinburgh.


Compound feed           A mixture of different       Concentrate         A generic term to describe
dietary ingredients blended together to form a       any non-forage dietary ingredient, usually for
complete feed for non-ruminants, or a supple-        herbivores. Concentrates include compound
mentary feed to complement forage for rumi-          feeds, protein concentrates, single raw materi-
nants. Compound feeds contain carbohydrate           als (also called straights) and supplements.
sources such as cereals and protein sources          The concentrate:forage ratio of a ration is the
such as oilseeds or fish meal, with mineral and       sum of these ingredients divided by the total
vitamin supplements. The ingredients are usu-        forage content of the ration, though some
ally milled to reduce particle size and aid mix-     classes of stock may be fed on 100% concen-
ing. Most compound feeds are pelleted for            trates, with no forage component.
                                            Conditioning                                        117




    Concentrates generally have greater con-        pensers are available for allocating concentrates
centrations of energy and protein than for-         to individual cows in small quantities and fre-
ages. They are also fermented more rapidly in       quent meals throughout the day. Alternatively,
the rumen. Rapid consumption of starchy             a proportion of the concentrate allocation can
concentrates in large quantities can upset          be mixed with forage to form a basal ration
rumen fermentation. Starch is rapidly fer-          that is supplemented on an individual cow basis
mented in the rumen, leading to a drop in           with the remaining concentrates, or the whole
rumen pH and build-up of lactic acid (acido-        concentrate allowance can be mixed with for-
sis). When rumen pH fall below 6.0, cellu-          age to form a complete feed. If concentrates
lolytic bacteria cannot digest the forage           and forage are fed separately, the concentrate
component of the ration and rumination              allowance may be varied according to individual
becomes less frequent. The buffering action of      milk yield (e.g. 0.4 kg l 1), or on a flat rate to
saliva is reduced, exacerbating the drop in         all cows. Research results suggest that total
rumen pH. Acute cases of acidosis arise when        milk yield is determined by the total allowance
animals accidentally gorge themselves on con-       of concentrates throughout the year, rather
centrates, often resulting in death within          than pattern of allocation.                (PCG)
hours. Mild acidosis occurs in dairy cows or
beef cattle given a high-concentrate diet and       Conception rate              Strictly defined as
may be associated with reduced forage diges-        the number of animals conceiving, expressed
tion, low milk fat content and laminitis.           as a percentage of the total number mated or
    Cattle fed on an all-forage diet normally       inseminated. It is not normally possible to
have volatile fatty acid concentrations in the      detect that an animal has conceived until
rumen of approximately 70% acetate, 20%             some time after the event so that, in practice,
propionate, 8% butyrate and 2% others. Feed-        conception rate is often synonymous with
ing concentrates increases the proportion of        pregnancy rate. It may be expressed as the
propionate in rumen fluid, since this volatile       non-return rate, which is the percentage of
fatty acid is an end-product of starch digestion.   animals not seen to return to oestrus within a
Propionate is a major precursor of glucose and      defined period after mating or insemination.
so increased propionate production from con-            Conception rate depends on the propor-
centrates results in increased circulating levels   tion of females that ovulate close to the time
of insulin and greater body fat deposition.         of insemination and on the proportion of ovu-
Concentrates are therefore useful for fattening     lating females whose ova are fertilized. This in
animals and for lactating animals in early lacta-   turn depends on the viability of the ova, the
tion that would otherwise be unable to con-         uterine environment and the number and via-
sume sufficient energy to meet the                   bility of available spermatozoa.
requirements of milk production. Concentrates           Provided that females are not malnourished,
are also the major source of undegradable pro-      nutritional levels tend to affect the number of
tein in ruminant diets which, for high-produc-      ovulations, rather than the occurrence of ovula-
ing animals, is an essential supplement to          tion. Severe underfeeding is likely to suppress
microbial protein produced in the rumen.            cycling and oestrous behaviour. The female is
    Concentrates are usually fed at a restricted    thus less likely to be mated, and there will be
rate in order to avoid disrupting rumen function    no effect on conception rate per se.
and also because they are more expensive than           Specific nutritional imbalances may affect
forages. Large allowances of concentrates           the reproductive tract environment. High levels
should be divided into two or more separate         of dietary protein have been associated with low
meals. Traditionally, concentrates were allo-       pregnancy rates in cows, for example. (PJHB)
cated to dairy cows during milking. The greater
milk yields achieved today require higher con-      Conditioning          The mechanical treat-
centrate allowances, and faster milking routines    ment of crops at the time of mowing. The aim
mean that it is not possible for cows to con-       is to provide a rapid rate of moisture loss from
sume all of their concentrate allowance in the      the crop with minimal loss of dry matter. Con-
milking parlour. Electronic concentrate dis-        ditioners are an integral part of the mower and
118                                      Connective tissue




can range from a simple mechanical tine that       reduction reactions in mammalian systems.
lacerates the crop, to a more complex mecha-       Some of these Cu enzymes have antioxidant
nism with rubber or metal rollers.      (RJ)       activity and are involved in the metabolism of
                                                   reactive oxygen species such as superoxide and
Connective tissue            A tough sheet of      hydrogen peroxide. Others have ferroxidase
fibrous tissue found as the outer membrane of       activity, oxidizing Fe2+ to Fe3+.
organs (liver, kidney, muscle or skin) or the           In most non-ruminant mammals, ingested
tough cord-like tissue that connects muscles to    Cu is absorbed primarily from the duodenum.
bones (tendons) or the tough fibrous tissue         The mechanisms of absorption involve trans-
that connects bones to cartilage, muscle or        port proteins that are located in the plasma
other bones (ligaments). Connective tissues        membranes of the enterocytes. These include
are comprised primarily of extracellular colla-    CTR1 for Cu influx and ATP7a for Cu efflux.
gen fibres that appear white. Another abun-         A genetic aberration in the gene for ATP7a
dant protein in some connective tissue is          produces a dysfunctional transporter allowing
elastin, which is yellow.               (TDC)      Cu to accumulate in the enterocyte, with little
                                                   transferred to the blood. Although the mecha-
Contamination          The presence of sub-        nisms of Cu absorption in farm animals have
stances not intentionally added and usually of     not been studied to this extent, they are prob-
an undesirable nature. Common examples             ably similar. After Cu is transferred to the
include: toxic elements occurring naturally or     blood, it is transported to the liver and other
picked up during transport next to inappropri-     organs bound to serum albumin. Similar trans-
ate substances or in dirty containers; pesticide   port proteins as found in the intestine proba-
residues from incorrect use; fruits or seeds of    bly effect Cu uptake into the liver and other
poisonous plants; or toxic fungal bodies such as   tissues; however, the efflux transporter in liver
ergot. Aflatoxins may develop in poor storage       is ATP7b. Aberrations in this gene cause Cu
conditions and microbial pathogens such as sal-    accumulation in the liver.
monella may contaminate feeds. Lack of care            Copper concentration in the serum or
in the feedmill may lead to one feed being con-    plasma is around 15 mol l 1, but slightly
taminated by another. It is particularly impor-    higher in females than males. During low
tant to avoid contaminating a non-medicated        intakes of dietary Cu in young animals, the Cu
feed with one containing a medicine.      (CRL)    concentration in plasma can decrease to one-
                                                   half the normal value within a few weeks. Adult
Convulsions           Electrolyte   imbalances,    animals are more resistant to Cu deprivation
especially magnesium deficiency, can upset the      than the young. If the deficiency is allowed to
electrical potential of brain neurones, causing    progress, the animals can die of an aortic dis-
them to be hyperexcitable. This can cause          secting aneurysm, caused by the reduction of
uncontrolled motor neurone excitation, leading     the Cu-dependent enzyme lysyl oxidase that
to irregular and spastic muscle contraction due    cross-links collagen and elastin fibres.
to excessive excitation of neurones within the         The outward signs of Cu deficiency in
brain.                                    (JPG)    mammals are less evident than with other
See also: Hypomagnesaemia                          mineral deficiencies. Food intake and weight
                                                   gain are not affected to a great extent but the
Cooking: see Heat treatment                        animals will develop anaemia. Copper-con-
                                                   taining enzymes will be reduced in activity and
Copper         Copper (Cu) is a mineral element    can result in increased susceptibility to oxygen
with an atomic mass of 63.546. It is an essen-     stress. Large blood vessels can weaken and
tial dietary component for all farm animals.       lead to aneurysms. Copper deficiency in
Copper is a transition element and has two         utero can lead to neurological damage in the
redox states, Cu+ and Cu2+. It is one of the       offspring that is irreversible. High zinc con-
most biologically active mineral elements and is   centrations in the diet can interfere with Cu
an indispensable part of many enzyme systems       absorption and lead to signs of Cu deficiency.
involved in electron transfer and oxidation–       Ruminant animals that consume diets mod-
                                              Cottonseed                                            119




estly high in molybdenum and sulphur are sus-         thesized by microbes in the hindgut. In some
ceptible to Cu deficiency because of the in            animals, such as the rabbit, the process is
vivo formation of thiomolybdate that binds Cu         more correctly referred to as caecotrophy and
and renders it unavailable for absorption.            the ingested material referred to as caecotropes.
    According to the US National Research             Small herbivores such as rabbits and guinea pigs
Council, the Cu requirement of most farm              selectively excrete fibre and retain non-fibre
species, including dairy and beef cattle, and         components in the caecum, where they are fer-
horses, is approximately 10 mg kg 1 diet for          mented. At intervals, the caecotropes (night fae-
all age groups. The requirement for pigs can          ces, soft faeces) are consumed. Coprophagy
range from 3 to 6 mg kg 1 diet, with the              and caecotrophy increase the digestibility of
young animal requiring more than the adult.           feeds, because of enhanced caecal fermentation
The Cu requirement for poultry ranges from 4          and a second transit of ingesta through the
to 5 mg kg 1; the young chick requires more           digestive tract.                             (PC)
than the adult.
    Farm animals are rather susceptible to Cu         Cori cycle        A metabolic cycle in which
toxicity. Hepatic necrosis has been observed          lactate produced from glucose by anaerobic
in calves fed 45 mg Cu kg 1 diet for 13               metabolism in muscle is recycled to the liver
weeks; however, adult cattle seem to show no          and converted back into glucose. Anaerobic
adverse effects after consuming 200 mg daily          glycolysis in muscle produces pyruvate, which
for up to 15 weeks. Sheep, on the other               is reduced to lactate by the NADH produced
hand, develop toxicity signs when exposed to          in glycolysis.                          (NJB)
as little as 30–80 mg Cu kg 1 diet for 20             Corn         Any growing cereal crop or har-
weeks, but when dietary sulphur and molybde-          vested grain may be referred to as ‘corn’,
num are low, Cu toxicity signs can develop            especially the predominant crop of a particu-
with as little as 11 mg dietary Cu kg 1. Young        lar area (such as wheat in England, oats in
swine can show toxicity signs when fed Cu in          Scotland or maize in the USA).          (ED)
excess of 250 mg kg 1 diet but Cu fed at lev-
els of 100–250 mg kg 1 can promote growth             Corrinoids          Compounds containing the
in weanling pigs. Toxicity signs manifest             basic octadehydrocorrin ring structure of vita-
themselves mostly as reductions in growth             min B12 and related compounds. Similar
rates and/or haemolytic responses.       (PGR)        structures are the iron porphyrin ring of haem
See also: Absorption; Availability; Iron;             in haemoglobin and the magnesium-contain-
Molybdenum; Thiomolybdates; Zinc                      ing porphyrin of chlorophyll.             (NJB)

                                                      Corticoids: see Adrenal
Further reading
Harris, E.D. (1997) Copper. In: O’Dell, B.L. and      Corticosterone: see Adrenal
   Sunde, R.A. (eds) Handbook of Nutritionally
   Essential Mineral Elements. Marcel Dekker,         Cortisol: see Adrenal
   Inc., New York, pp. 231–273.
Suttle, N.F. (1991) The interactions between cop-
                                                      Cottonseed         The seed of cotton (Gossyp-
   per, molybdenum, and sulphur in ruminant           ium spp.) is obtained as a by-product of cotton
   nutrition. In: Olsen, R.E., Bier, D.M. and         fibre production, about 2 t of seed for each
   McCormick, D.B. (eds) Annual Review of             tonne of fibre. The seeds contain about 200 g
   Nutrition. Annual Reviews Inc., Palo Alto, Cali-   kg 1 of oil, which contains a high proportion of
   fornia, pp. 121–140.                               unsaturated fatty acids. The oil is often extracted
                                                      by compression and the fibrous husk is pressed
Copra: see Coconut                                    with the seed kernel. The resultant cake is
                                                      known as undecorticated cake and has a crude
Coprophagy            The consumption of fae-         fibre content of around 300 g kg 1; the decorti-
ces, generally implying the animal’s own faeces.      cated cake has about 90 g kg 1. This difference
Nutritional benefits include the consumption of        in fibre considerably affects the nutritive value of
B-complex vitamins and bacterial proteins syn-        cottonseed, especially for non-ruminants.
120                                              Coumarin




Decorticated meal has a protein content of              ration for the first 4–7 weeks and increase the
400–500 g kg 1, the undecorticated meal                 energy content just for the last 3 weeks. The
200–250 g kg 1. The protein is first limiting in         amount of concentrates fed near to calving
lysine. Undecorticated cottonseed meal has an           depends on the condition of the cow and the
apparent metabolizable energy for poultry of            desired milk output, but would typically be 2–4
about 8 MJ kg 1 while for ruminants it is about         kg day 1. Feeding a high nutrient-density diet
12 MJ kg 1. Cottonseed meal is rarely included          before lactation prepares the cow for milk pro-
in the diets of poultry or at levels of more than       duction by, firstly, supporting growth of the
about 100 g kg 1 for mature ruminants because           rumen papillae, which takes about 5 weeks of
it may cause digestive problems. Cottonseed             exposure to cereals, and, secondly, by allowing
and the meal contain condensed tannins, a               the cow to lay down additional body reserves
polyphenolic aldehyde, gossypol and two cyclo-          that can be used in early lactation, when volun-
propenoid fatty acids (malvalic and sterculic           tary feed intake is insufficient to supply the
acids). The tannins are present in small quanti-        nutrient requirements for milk production.
ties (less than about 30 g kg 1) and may reduce         However, cows that are fat at calving consume
nutrient utilization slightly. The older varieties of   less feed post partum than cows that are thin.
cotton can contain up to about 20 g kg 1 but            They rely more on catabolizing body tissue for
the newer cultivars have much lower concentra-          their energy and, to some extent, protein
tions in the seed.                                      requirements. A large negative energy balance
    Like tannins, gossypol chelates mineral ele-        in the first 100 days of lactation increases the
ments and may reduce their absorption. Iron             time to first ovulation and reduces progesterone
salts are sometimes added to chelate the                secretion, leading to a longer calving index.
gossypol and thus reduce the effects in ani-                Calcium intake requires careful manage-
mals. Processing the seed may cause reaction            ment before and immediately after calving.
of gossypol with lysine, reducing its availabil-        During early lactation the output of calcium
ity. Gossypol has an adverse effect on rumen            increases considerably, because of milk pro-
microbes and is also associated with reduced            duction, and this may be more than the cow
reproductive capacity in animals. Feeding cot-          can provide from body stores in the bone tis-
tonseed to sheep has been shown to reduce               sue. Calcium absorption and excretion are
protozoal numbers but it is uncertain if this           regulated by the production of parathyroid
was due to the effects of the gossypol or of            hormone. If it is possible to restrict calcium
the oil. Other adverse effects of gossypol              intake before calving to approximately 3 g
include coloration of egg yolks in hens’ eggs           kg 1 dry matter (DM), increased activity of
due to chelation of minerals. The cyclo-                parathyroid hormone increases the absorption
propenoid fatty acids disturb lipid metabolism          of calcium from the gastrointestinal tract.
in animals and reduce performance.               (TA)       In early lactation, feed intake does not
                                                        increase as rapidly as milk production, creating
Coumarin: see Dicoumarol                                a deficit in the nutrients required for maximum
                                                        milk production. It is normally not until mid
Cow         The mature female of any species            lactation that energy balance is restored. The
of Bovidae (cattle). The term is usually                deficit is met by the mobilization of body fat
applied after the animal has delivered her first         reserves and to some extent body protein and
calf. Before that she is called a heifer. (PJHB)        mineral stores. A high-energy diet accelerates
                                                        the return to maximum intake, which is one
Cow feeding            The dairy cow has been           advantage of allocating more concentrates to
selectively bred to produce considerably more           the early lactation period. An excessive weight
milk than is required by any calf and so lacta-         loss during early lactation reduces milk yield,
tion, particularly at the beginning, requires a         lessens the chance of conceiving and maintain-
much greater intake of nutrients than the tradi-        ing a viable embryo and increases the risk of
tional high-fibre diet of cattle. Preparation for        acidosis. If cows have a low level of body
lactation is important and normally cows do             reserves, it is less likely that they will be able to
not lactate for 7–10 weeks before calving. Dur-         endure a period of underfeeding without milk
ing this time farmers usually feed a high-fibre          yield being reduced. If forage has to be
                                           Cow feeding                                            121




restricted towards the end of winter because of    larly if it is collected into cans in the feeding or
inadequate supplies, both the expected dura-       living area of the cowshed and transferred to
tion and the severity of the restriction should    churns. For example, brassicas and beets may
be taken into consideration when deciding          produce a taint if fed within 3 h of milking and
whether to purchase additional feeds.              so should preferably be fed after milking.
    Milk fat is produced both by the synthesis         In most countries grass, or other feeds for
of fatty acids in the mammary gland and by         grazing, cannot grow all year and so farmers
the absorption and secretion into milk of          conserve surpluses from times when growing
dietary fatty acids. In microbial digestion, the   conditions are good so that they can be fed to
fatty acid profile of the feed is modified. Acetic   the cattle during the winter months, when it is
acid is the main precursor for milk fat synthe-    too cold for grass to grow, or in the dry sea-
sis and, as the acetogenic bacteria digest plant   son, when there is insufficient moisture. In
cell wall, the fibre content of the diet is the     temperate countries fodder is mainly con-
most important determinant of the fat content      served as silage, which is cut at a younger
of the milk. The ratio of lipogenic nutrients      stage of growth than hay and, therefore,
(acetic acid, butyric acid and long-chain fatty    tends to be more nutritious. In the humid
acids) to glucogenic nutrients (propionic acid,    tropics, making good quality silage is more
glucose and some amino acids) therefore            difficult because the high temperature and
determines milk fat content, in particular the     humidity make controlling the fermentation
ratio of acetate to propionate. Fibre digestion    more difficult. It also requires more equipment
is impaired if the rumen pH is less than 6.3,      and facilities than haymaking. Maize silage is
and feeding large quantities of concentrates       popular with cattle farmers because it has sev-
that are rapidly fermented in the rumen to acid    eral advantages over grass silage. Silage can
end-products should be avoided. Rumen pH           be fed either directly from a clamp, so-called
can be maintained by feeding alkali-treated for-   self-feeding, or it can be extracted from the
age or grain, or by stimulating the production     clamp by machine and fed along a passage-
of saliva, which contains buffers based on both    way or in a circular feeder. If the silage is fed
sodium and potassium. The incorporation of         in a passageway, cows should be restrained
unsaturated fatty acids into milk is possible if   behind a barrier that allows them to put their
fats are protected from rumen fermentation.        heads through to feed, but not to walk on the
Normally no more than about 6% of unpro-           silage or pull their heads back through the
tected fat should be included in the diet, as it   barrier while they are still eating silage.
has adverse effects on rumen digestion.                Hay relies on preserving grass by removing
    Milk protein is mainly casein (about 70%),     the moisture that microorganisms require for
the remaining 30% comprising -lactoglobu-          survival. Energy losses from the grass plant
lin, -lactalbumin and immunoglobulins. Varia-      are often very high during haymaking, due to
tions in milk protein concentration in response    continued plant respiration. However, if the
to changes in nutrition are less than those of     same grass could be used to make either hay
milk fat, but there is a clear relationship        or silage, the protein value of the hay would
between the energy supply to the cow and           usually be greater than that of silage, because
milk protein content. The response of milk         there is less protein denaturation during the
protein content is mainly due to the reduced       conservation process.
use of amino acids to supply energy. Cows              In many parts of the world, straw and other
that are catabolizing body lipids to provide for   crop residues, such as maize stover, are an
their energy requirements, therefore, tend to      important feed for cattle. Their available
have low concentrations of milk protein, as        energy content is low, as most of the energy is
some of the feed protein will be utilized for      locked up in the form of cellulose and other
energy. The optimization of the amino acid         structural carbohydrates that are lignified.
content of the diet could become more impor-       Cows will not consume much straw, because
tant if the control of nitrogen emissions from     its rate of breakdown in the rumen is slow.
cattle should become more urgent.                  The protein content of straw is much less than
    Milk is likely to acquire taints from feeds    that required by most cows, often only 40 g
when it is exposed to the environment, particu-    kg 1 DM. The concentrations of minerals and
122                                        Cow lactation




vitamins are also low. Thus for high-yielding       Diet formulations for early, mid and late lactation cows.
cows straw has little nutritional value but it
                                                    Early                               Mid       Late/dry
helps to maintain rumen function and animal
health. Straw can be upgraded by treating it        Yield level (kg per cow day 1)     30–40     20 10
with sodium hydroxide or ammonia, which             Forage DM as proportion of
reduce the lignification of the structural carbo-       total DM                         0.3       0.5 0.7
hydrate. It can also be harvested together with     Energy density (MJ kg 1 DM)        12        11 10
                                                    Crude protein (g kg 1 DM)          17        14 12
the cereal grain in the form of ‘whole-crop’ or
                                                    Modified acid-detergent fibre
arable silage.                                         (g kg 1 DM)                     16        25 30
    Concentrated feeds, or concentrates, are        Calcium (g kg 1 DM)                 8         6 5
based on cereals, or other feed high in energy      Phosphorus (g kg 1 DM)              4.5       3.5 3.0
and protein. They are usually made into a pel-      Magnesium (g kg 1 DM)               1.8       1.5 1.5
let, or compound, with the addition of a binding    Sodium (g kg 1 DM)                  1.8       1.5 1.5
agent, most often sugarcane molasses. A dairy
                                                                                                      (CJCP)
cow can give yields of 7000 l per lactation on
high-quality forage alone, but in most situations   Cow lactation               The lactation of the
farmers get an economic response to providing       cow commences at calving. Milk production
at least a low level of supplementary concen-       increases progressively in the first 2–3 months
trates. In developing countries, less concentrate   of lactation, and peak lactation normally
supplements are fed than in the industrialized      occurs between week 8 and week 12 after
countries and they are often of lower quality,      calving. Thereafter, milk yield declines until
because cereals are relatively expensive and are    the cow is dried off 2 months before she is
reserved mainly for feeding to humans. The          due to produce her next calf. Thus, the usual
allocation of concentrates to dairy cows should     total length of the cow lactation is 305 days
take account of their physiological state, i.e.     and the dry or transition period is normally
whether they are lactating, pregnant or neither.    60 days in length.
Dairy farmers generally prefer to feed most con-        Lactation is normally considered in three
centrates to those cows giving the most milk,       phases: early lactation, the first 100 days after
whatever their forage feeding system, but loose-    calving; mid lactation, days 100–200 of lacta-
housed cows fed high-quality forage ad libitum      tion; late lactation, days 200–305 of lactation.
respond similarly whatever their milk yield.        The pattern of voluntary food intake is similar
Feeding all the cows their concentrates at a flat    to that of milk production but maximum food
rate through the winter period has the advan-       intake is not normally achieved until the fourth
tage of simplicity and it can be fed on top of or   month of lactation. The rise in food intake is
mixed in with their forage, rather than through     therefore slower than the increase in milk
individual feeders in the parlour or cow housing.   yield, particularly in the first 2 months of lacta-
The risk of upsetting rumen digestion with high-    tion. As a result the cow’s requirement for
concentrate diets and causing low milk-fat con-     energy often exceeds her intake of energy; she
centrations or acidosis has led to such diets       is in negative energy balance and loses body
being based on digestible fibre, e.g. from beets,    weight in early lactation. This loss in weight is
rather than starch from cereals. The starch in      normally replaced in the final 3 months of lac-
compound pellets is exposed to rapid degrada-       tation, when milk yield is relatively lower than
tion by the rumen bacteria.                         in mid and early lactation. The target for feed-
    Dairy cows can be given a complete diet –       ing the dairy cow should be to achieve a simi-
usually a mixture of silage and concentrates        lar body weight and condition score at the end
mixed up in a portable feeding wagon. An            of the lactation as at its start.
advantage of complete diets is that inexpen-            The feeding strategy to meet the high nutri-
sive by-product feeds can be incorporated into      ent requirements of the cow in early lactation is
a mix, and feeds with low palatability can be       to maximize voluntary intake as soon as possi-
masked by the strong taste of silage. Typical       ble. The transition from the dry period to early
diet formulations for early, mid and late lacta-    lactation should be smooth, and the cow is
tion or dry cows are given in the table.            often introduced to a lactation diet in the final
                                            Cow lactation                                        123




21 days of the dry period to allow the rumen             Lactating cows are normally milked twice
microflora to adapt to the change in dietary          daily, though where Bos indicus cattle pre-
ingredients from the dry-cow diet to the lacta-      dominate, the calf must be present to stimulate
tion diet. The energy density of the diet is         the release of oxytocin and milk ejaculation by
increased in early lactation in an attempt to        the cow. Bos indicus cattle may only be
minimize the deficiency in energy intake at this      milked once daily, and their milk yield may be
time. The early lactation diet often comprises a     reduced if the calf is allowed to suckle before
higher proportion of rapidly digested concen-        the cow is milked. In contrast, herds of Bos
trated feeds, including starch and lipids, and a     taurus cows may be milked three times daily.
lower proportion of slowly digested forages          This practice increases milk output by about
than the mid and late lactation diets. The con-      15%. In high-yielding herds the additional
centration of metabolizable protein is also          expense of the extra milking may be offset by
higher in early lactation diets than in diets for-   the value of the increased milk yield.
mulated for mid and late lactation.                      A recent innovation is the introduction of
    In mid lactation, the nutritional strategy is    automatic milking systems in which the cow is
aimed at minimizing the rate of decline in milk      allowed to choose when she is milked. Most
yield, which can often be as much as 2.5%            cows opt to be milked four to five times daily,
per week. Ideally, the milk yield of the cow         usually with a reward of a meal of food follow-
should remain as close to peak yield as possi-       ing each milking. This system of rewarding
ble during the second 100 days of lactation,         cows for entering the automatic milking par-
though the onset of pregnancy, with associ-          lour includes recording cows’ entry so that
ated changes in the hormonal balance of the          any cow not presenting itself can be checked
animal, is reflected in a change in the parti-        for signs of ill-health.
tion of nutrients from lactation to the growth           The composition of milk changes during
of the placenta and fetus. Thus, if milk yield       lactation. At calving the first milk, colostrum,
decreases substantially in mid lactation and         is particularly rich in fat, protein,
the diet is not reformulated to take account of      immunoglobulins, minerals and vitamins. In
the reduction in nutrient requirements, the          early lactation, when the volume of liquid pro-
cow is liable to gain weight during this period.     duced is at its greatest, the concentration of
    Late lactation is the period when the volun-     solids in milk is usually at its lowest. The con-
tary intake of nutrients is most likely to exceed    centrations of milk fat and protein increase
requirements for milk production, and as a           progressively as the volume of milk secreted is
result the cow normally gains weight during          reduced later in the lactation.
this phase of the lactation. Slowly digested for-        Metabolic disorders are most likely to occur
ages should comprise the majority of the ani-        in early lactation. The major risks are hypocal-
mal’s nutrient supply. Supplementary protein         caemia (milk fever), hypomagnesaemia (lacta-
may be required if the forage is deficient. The       tion tetany or grass tetany) and acetonaemia or
supply of essential mineral elements should be       ketosis (twin lamb disease). Hypocalcaemia is
checked and any deficiencies rectified. Straw is       most likely to occur soon after calving, when
often used at this stage of lactation as a way of    the output of calcium in milk is suddenly
reducing the energy density of the diet.             increased and the animal cannot absorb suffi-
    Cows are usually dried off at least 60 days      cient dietary calcium or mobilize sufficient
before the predicted date of calving, to allow       reserves of calcium from body stores to meet
the udder to recover from the previous lacta-        the increased requirement. Immediate treatment
tion and to condition the cow for the next lac-      with a readily available source of calcium, cou-
tation. Drying off is achieved by stopping           pled with supplementary calcium in the diet,
milking abruptly. This can cause problems if         usually alleviates the condition. Careful manage-
the cow is still yielding a relatively large quan-   ment of the mineral nutrition of the cow during
tity of milk, and for this reason some very          the dry period can reduce the risk and incidence
high-yielding cows have extended lactations,         of milk fever. Hypomagnesaemia can also occur
especially if they are not due to calve for a fur-   soon after calving and is often associated with
ther 80–100 days after their normal 305-day          the start of the grazing season, when the animal
lactation, because of delayed conception.            is presented with herbage of lower magnesium
124                                          Cow pregnancy




concentration than the previous winter diet.           and mammary glands and also the nervous
The condition can also occur following a short         system. The heart, muscles and bones are
period of inappetence, when magnesium intake           eventually formed from the mesoderm
is suddenly reduced. Hypomagnesaemia is pre-           whereas the other internal organs are derived
vented by supplementing the diet with magne-           from the endoderm layer. By day 45, forma-
sium. Acetonaemia is caused by a deficiency of          tion of the primitive organs is complete.
energy in the diet and may be triggered by a               The embryo is able to exist for a short time
period of inappetence caused by an infectious          by absorbing nutrients from its own tissues and
disease or sudden deprivation of food, or by a         from the uterine fluids, but it ultimately becomes
chronic deficiency of energy in the diet itself.        attached to the endometrium by means of its
Prevention of acetonaemia is by ensuring that          membranes through which nutrients and
the animal’s appetite is maintained at all times,      metabolites are transferred from mother to fetus
and that the early-lactation diet is relatively high   and vice versa. In the cow, antibodies cannot
in readily digested sources of energy.        (JMW)    pass the placental barrier and the calf is thus
                                                       dependent on the first milk (colostrum) pro-
Cow pregnancy              Pregnancy in the cow        duced by its mother at parturition to acquire
lasts from the time of fertilization of an ovum        immunity from her. The attachment process is
or ova in the oviduct until the resulting concep-      known as implantation and may begin as early
tus leaves the uterus. In a successful pregnancy       as day 20, although definitive placentation does
a live calf, with its associated placenta, is born     not occur until days 40–45. If the cow is carry-
approximately 9 months after fertilization. The        ing twins, the placentae and their blood supplies
average length of gestation is typically               tend to grow together. Thus, sex hormones
280–285 days but depends to some extent on             from a male which is co-twin to a female are
the breed, particularly of the sire. For example,      likely to interfere with the development of her
when used to inseminate Friesian cows, bulls of        sexual organs, resulting in a sterile female called
such large breeds as the Charolais, Simmental          a freemartin. The male may be affected to a
or Chianina tend to produce longer gestation           lesser extent by hormones from the female.
periods than Friesian or Hereford bulls.               Twin calves are somewhat less likely to survive
    A cow normally ovulates one ovum at each           than singles, especially if they are developing in
oestrous period. Occasionally two or more are          the same uterine horn.
ovulated (see Twinning). More rarely, a fertil-            Fetal growth is exponential throughout ges-
ized embryo may divide to form identical twins.        tation, the rate increasing as pregnancy pro-
    Immediately after fertilization, the ovum          gresses. Thus, fetal requirements for energy,
begins to divide, forming a solid cluster of cells     protein and minerals increase rapidly, especially
or blastomeres known as a morula (mulberry             during the last third of gestation (see table).
shape). This process takes 5 or 6 days, during
                                                       Deposition of nutrients and energy in the uterus of the
which the embryo continues its passage down
                                                       cow. (Source: McDonald et al., 1995.)
the oviduct and enters the uterus. From about
day 6 after fertilization, the ovum hollows out                                Deposited in uterus (per day)
to become a blastocyst, which consists of a
single spherical layer of cells, the trophoblast,      Days after         Energy Protein Calcium Phosphorus
                                                       conception          (kcal)  (g)     (g)      (g)
with a hollow centre and an inner cell mass at
one edge. The inner cell mass is destined to           100                   40       5        –         –
form the embryo, whilst the trophoblast pro-           150                  100      14       0.1        –
vides it with nutrients and will form the fetal        200                  235      34       0.7         7
component of the placenta. At about day 8              250                  560      83       3.2       22
the blastocyst ‘hatches’ from its shell (the zona      280                  940     144       8.0       44
pellucida) and begins to elongate rapidly. From        Maintenance(a)      7000     300       8.0       12
about day 14 the development of the so-called          (a)   Approximate net daily maintenance requirement of a
germ layers begins within the inner cell mass.               450 kg cow.
These are termed the ectoderm, mesoderm
and endoderm. The ectoderm gives rise to the              Uptake of nutrients by the uterus and its
external structures such as skin, hair, hooves         contents is less efficient than for the cow’s body
                                                Creatine                                          125




in general, so that nutritional requirements to       Cowpea          A leguminous plant (Vigna
meet the demands of pregnancy in the cow are          unguiculata) grown in the semi-arid and sub-
actually higher than the amounts deposited in         humid tropics, primarily for their seeds. These
the uterus. Furthermore, fasting metabolism           contain 200–300 g crude protein kg 1 and
during pregnancy is higher than that in non-          have an apparent metabolizable energy of
pregnancy, because of a higher basal metabo-          about 14 MJ kg 1 for both sheep and poultry.
lism in the mother herself rather than the heat       The proteins are relatively low in sulphur
produced by the fetus. This may be a response         amino acids. The seeds contain protease
to changes in hormone levels during pregnancy         inhibitors: this limits the usefulness of raw
and it increases throughout pregnancy. This,          seeds. The protease inhibitors can be inacti-
together with the liveweight increase that should     vated by heat treatment. Cowpeas may be
occur, leads to a gradual rise in the maintenance     used as a green or dried fodder with a protein
energy requirement. Thus, the requirement for
                                                      content of about 120 g kg 1.               (TA)
energy in pregnancy is increased by far more
than would be deduced from the storage of
                                                      Crambe            An annual of the Brassica
energy in the fetus. Nevertheless, in early preg-
                                                      group, native to the Mediterranean area and
nancy, nutritional requirements for pregnancy
                                                      cultivated in North and Central America.
per se are small, especially in relation to the
requirements for maintenance and for milk pro-        Crambe abyssinica is grown for its oil, which
duction in the mid-lactation cow. It is only in the   is used in industry and contains 50–60% eru-
last 3 months of pregnancy that special dietary       cic acid. The residual crambe seed meal has
provision has to be made for the growth of the        value as a supplement in livestock and poultry
fetus. At this stage, net requirements for protein    feeds because of its high protein content
and minerals such as calcium and phosphorus           (300–400 g kg 1) and well-balanced amino
are quite substantial. Additionally, in the last 2    acid content. However, the seeds contain anti-
weeks, when mammary growth is fastest, a rela-        metabolites     including   goitrogens,    and
tively modest 45 g protein day 1 is deposited in      unprocessed meal is limited to 5% inclusion in
the udder. Net energy requirements are still          diets for adult ruminants and is unsuitable for
quite small in relation to maintenance require-       inclusion in non-ruminant feeds.         (JKM)
ments. Furthermore, in the dairy cow, there will
be no energy demands for lactation in the last 2      Crazy chick disease (encephalomalacia):
months or so of pregnancy. Dry pregnant dairy         see Vitamin E
cattle normally have a dry-matter appetite in
excess of their requirements. It is thus relatively   Creatine          HN=C(NH 2)·N·(CH 3)·CH 2·
easy for a cow to gain weight during this period      COOH. Creatine is produced in a number of
and it is usually necessary to restrict energy        steps, first in the kidney and then in the liver,
intake at this time to avoid the cow calving at       from arginine, glycine and methionine. It is
too high a condition. The latter can lead to calv-    converted to creatine phosphate in muscle
ing difficulties and subsequent metabolic disor-       (ATP + creatine         creatine phosphate +
ders, such as fatty liver syndrome, which can         ADP), where it serves as an energy reserve to
seriously affect production and reproductive
                                                      convert ADP to ATP during times of high
performance. Intake can be restricted by feed-
                                                      ATP use. Creatine is oxidized and then
ing a single forage, such as grazed grass or
                                                      excreted in the urine as creatinine.
silage, or by including chopped cereal straw in
the diet to raise its cell wall content.   (PJHB)                                       O

Reference and further reading                                      N
AFRC (1993) Energy and Protein Requirements of
   Ruminants. CAB International, Wallingford, UK.                          N
                                                                                         O
McDonald, P., Edwards, R.A., Greenhalgh, J.F.D.
   and Morgan, C.A. (1995) Animal Nutrition,                     N
   5th edn. Longman, Harlow, UK.
Peters, A.R. and Ball, P.J.H. (1995) Reproduction                                               (NJB)
   in Cattle, 2nd edn. Blackwell Science, London.     See also: Adenosine triphosphate
126                                          Creatinine




Creatinine         The anhydride of creatine        Crop fractionation:         see   Fractionation,
and the end-product of creatine breakdown           green-crop
(by loss of H2O and Pi ) in muscle followed by
total excretion by the kidney. Creatinine           Crop residues: see Stover; Straw; Wine-
excretion is related to muscle mass and             making residues. See also: individual crop
thought to be constant over 24 h. For this
reason it is used in clinical settings as a basis   Cruciferae          Cabbage (Brassica) family,
to calculate total 24 h urine excretion from a      consisting of some 300 genera and 3000
single urine sample.                       (NJB)    species, including cabbage, sea cabbage, kale,
                                                    Brussels sprouts, cauliflower, broccoli,
Creep feeding            The feeding of supple-     kohlrabi, oilseed rape, mustard, radish,
mentary diet to suckling animals, most com-         crambe and related weeds and herbs. (JKM)
monly applied to piglets. This practice allows
piglets to compensate for any deficiencies in        Crude fibre           A collective term for com-
sow milk production and become gradually            plex carbohydrates, mainly celluloses and
accustomed to eating solid food; it also            lignin, that are insoluble in water, dilute acid
induces development of the digestive enzymes        and dilute alkali. There are various ways of
necessary for breakdown of complex carbohy-         estimating fibre, each of which defines a some-
drates on which they will be dependent for          what different fraction. In the proximate analy-
energy after weaning. Because of the high           sis of foods (the Weende system) crude fibre is
nutritional quality of sow milk, piglets gener-     measured by digesting a feed sample succes-
ally consume very little solid food before 3        sively with dilute acid (1.25% sulphuric acid)
weeks of age. However, if weaned later than         and dilute alkali (1.25% sodium hydroxide).
this, creep feed will be consumed increasingly      Soluble components such as sugars, starch, fat
as milk supply declines and becomes inade-          and protein are thereby removed, leaving an
quate. Thus, whilst creep feeding of piglets        insoluble residue. The weight loss on ignition
weaned at 3 weeks of age or younger is gen-         of this dried residue represents crude fibre.
erally of little benefit, piglets weaned at later    Other methods for examining complex, insolu-
ages will show increased growth rate both           ble carbohydrate in feeds have involved the
before and after weaning.                           use of a neutral detergent that removes soluble
    There are large and unexplained differ-         material and leaves behind cellulose, hemicellu-
ences, both within and between litters, in the      lose and lignin (neutral detergent fibre). Subse-
quantity of creep feed consumed. To achieve         quent boiling with an acid detergent hydrolyses
good intake, it is necessary to feed a highly       the hemicellulose, leaving behind cellulose and
digestible and palatable diet containing a high     lignin (acid detergent fibre). Oxidation of lignin
proportion of milk products. Intake is further      with potassium permanganate leaves cellulose
encouraged by freshness of feed, achieved by        and ash. Ignition of this residue gives a value
feeding little and often, and by presentation in    for cellulose.                            (CBC)
a feeder in which the diet is easily visible and
accessible.                                (SAE)    Crude protein           The crude protein con-
See also: Piglets                                   tent of a feed, or other biological material, is
                                                    defined as its N content multiplied by the fac-
Crop         Synonymous with ingluvies, a           tor 6.25. The value of this factor is based on
thin-walled extension of the oesophagus of          the observation that N occurs in different pro-
birds, located to the right side of the neck.       teins in a fairly constant proportion, 16% on
When full of food, the crop is easily palpated.     average. In determining the crude protein con-
Its function is to store ingested food when the     tent of a material its N content is measured,
gizzard is full. Movement of its muscular walls     usually by a Kjeldahl procedure. Crude protein
allows the food to soften and swell before          is not an exact measure of the protein content
chemical digestion in the proventriculus. The       of a material, because different proteins have
crops of well-fed birds are rarely empty.           different proportions of amino acids and their
                                        (MMax)      N content may thus vary a little from 16%,
                                         Crustacean feeding                                      127




and also because not all the N present in bio-      became interested in intensifying the produc-
logical materials is in the form of protein.        tion of crustaceans, natural feeds quickly
Compounds, other than protein, that contain         became a limiting factor. The lack of suitable
N are generally classed as non-protein N.           formulated feeds and, more importantly, the
These compounds are diverse in structure and        paucity of information on what was needed to
function; they include free amino acids,            make formulated diets for crustaceans, stimu-
amines, amides, purines, pyrimidines and            lated research interests in aquaculture centres
nitrogenous lipids. The level of non-protein N      throughout the world.
in most animal feeds and tissues is very small          The initial flurry of nutritional research
compared with the level of protein N. In addi-      encompassed a fairly diverse group of crus-
tion, much of the non-protein N in feeds may        taceans, including lobster, shrimp, the fresh-
be utilized by animals for the synthesis of non-    water prawn and crayfish but today this has
essential amino acids or, in the case of rumi-      narrowed to focus primarily on marine
nants especially, for the synthesis of microbial    shrimp. Commercial pond production of
protein. Although the use of an average con-        marine shrimp grew exponentially during the
version factor of 6.25 does not lead to an          1980s to become a significant industry in a
exact value, the protein content of feeds and       number of tropical countries. Early culturists
the protein requirements of farm animals are        almost always used an extensive approach
invariably expressed in this way.         (CBC)     that depended on enriching the natural pro-
See also: Kjeldahl; True protein                    ductivity of the pond ecosystems to provide
                                                    food for the shrimp. However, intensification
Crushing           Crushing usually refers to the   in response to continuing market demand
pressing of oilseeds in order to extract their      necessitated the direct addition of feeds to
oil. Oil-rich vegetable seeds, such as soybean      increase production per pond area. As a con-
(20% oil), oilseed rape (46%) and linseed           sequence, crustacean nutritional studies
(39%), are first dehulled and then crushed           became centred on providing information
between rollers or in a screw press. The resul-     applicable to marine shrimp and the need to
tant oil is collected, further purified and used     formulate artificial feeds for their culture.
for other purposes. The remaining meal is               Culturing of marine shrimp and many other
known as expeller or cake and still contains        crustaceans is made more difficult by the fact
approximately 10% oil. This can either be           that they have complicated life cycles, with
used as an animal feed or, more commonly, it        each stage requiring a distinct type of feed.
undergoes further chemical treatment to                 Such a life cycle is not unusual for crus-
extract the remaining oil.                          taceans of aquaculture interest. The nauplius
    Crushing can also refer to rolling, espe-       sustains itself on stored yolk but the rest of the
cially of cereals such as oats and barley, to       hatchery (sub-juvenile) stages have distinctive
prepare them for feeding. This is also known        requirements. Protozoea feed exclusively on
as ‘bruising’.                              (MG)    algae or other similar-sized microscopic feed-
                                                    stuffs. Increasingly, specific species of algae
Crustacean feeding             Fisheries biolo-     are cultured to provide an optimum feed for
gists have always had some interest in the          the protozoea stage. After a few days the pro-
type of food needed by large crustaceans such       tozoea stage moults into a mysis stage that
as lobster, shrimp or prawn. These animals          requires zooplankton rather than phytoplank-
were known to thrive on a variety of molluscs,      ton for continuing growth. The shrimp indus-
worms and other invertebrates found in              try is heavily dependent on feeding
aquatic environments. Aquaculturists inter-         brine-shrimp nauplii that have been freshly
ested in culturing crustaceans used this knowl-     hatched from cysts to support mysis produc-
edge to maintain crustaceans in the laboratory      tion. Finally, as the mysis stage moults into
and, in the case of shrimp and the prawn, to        the megalopa (or post-larva as the industry
produce limited numbers in ponds where              refers to it) larger types of zooplankton are
abundant supplies of natural feeds were pre-        needed. It is only at this last stage that formu-
sent. However, in the 1970s as culturists           lated rations are exclusively used.
128                                           Crustacean feeding




                OFFSHORE                                               COASTAL            ESTUARY



                             Mysis                    Megalopa

                   Protozoea                                                             Juvenile




            Nauplius

                                                                        Subadult

   Fertilized
       eggs
                                      Adult



Life cycle of a typical marine shrimp species.


    Most crustaceans require ten essential              quality and the contribution of natural food
amino acids, essential fatty acids (EFA), vita-         organisms in the pond system. Quantitative
mins and minerals for their growth, survival,           dietary requirements for arginine, histidine,
reproduction and health. Unlike fish and other           isoleucine, leucine, lysine, methionine, pheny-
terrestrial animals, they require sterols and           lalanine, threonine, tryptophan and valine
phospholipids,       particularly    phosphatidyl       have been determined for P. japonicus. Infor-
choline, as indispensable nutrients. Choles-            mation on carbohydrate utilization by crus-
terol is more effective in promoting growth             taceans is limited. Generally, simple sugars are
and development of crustaceans including lob-           poorly utilized by shrimp. Starch is commonly
ster and penaeid shrimps. Juvenile Penaeus              used as a carbohydrate source in shrimp diets
japonicus require 1% eicosapentaenoic acid              and its protein-sparing effect on energy utiliza-
(20:5 n-3) and docosahexaenoic acid (22:6 n-            tion has been demonstrated in P. monodon.
3) in their diet. Several crustaceans (P. japoni-       Chitin is the major structural component of the
cus, Penaeus orientalis, Macrobrachium                  exoskeleton of crustaceans, and some benefit
rosenbergii and Palemon paucidence) have                of supplemented chitin (0.5%) but not glu-
limited ability to convert linolenic acid (18:3 n-      cosamine has been reported in P. japonicus.
3) to 20:5 n-3 and 22:6 n-3. The recom-                     Most vitamins that have been established
mended dietary phospholipid concentration               as essential nutrients for fish and terrestrial
for various penaeids ranges from 0.84% for              animals are also considered to be essential for
Penaeus chinensis to 1.25% for Penaeus                  various crustacean species. The optimum lev-
penicillatus and Penaeus monodon. Recom-                els reported for penaeid shrimp include the
mended lipid levels for commercial shrimp               following (IU or mg kg 1): vitamin D, 4000
feeds range from 6% to 7.5% and the level               IU; vitamin E, 100 mg; vitamin K, 30 mg; thi-
should not exceed 10% of the diet.                      amine, 15–100 mg; riboflavin, 20 mg; pyri-
    Protein is an important component of crus-          doxine, 80 mg; niacin, 400 mg; biotin, 2 mg;
tacean diets. The optimum protein level for             vitamin B12, 0.2 mg; inositol, 2000–4000
growth of penaeid shrimps ranges from 28 to             mg; choline chloride, 600 mg; vitamin C,
57%. Wide variations in these values among              20–215 mg. Dietary deficiencies of these vita-
and within species in various studies have been         mins have been shown to cause reduced
due to the differences in species, size, protein        growth of penaeid shrimp but specific defi-
quality, utilization of non-protein nitrogen for        ciency signs have not been reported except
energy, stability of pellet, feeding rate, water        vitamin C. Black death syndrome, character-
                                            Cutting date                                         129




ized by blackened lesions of the digestive tract    amount of feed offered should not exceed the
and other tissues, is a typical sign of vitamin C   capacity of the system to accumulate the
deficiency.                                          waste products and to maintain sufficient lev-
    Dietary deficiencies of most minerals have       els of dissolved oxygen.         (DEC, SPL)
been difficult to produce in crustaceans             See also: Shrimp; Prawn
because of the presence of these minerals in
fresh water and sea water. Marine shrimp, P.
japonicus do not require calcium, magne-            Further reading
                                                    Fast, A. and Lester, J. (eds) (1992) Marine Shrimp
sium, iron or manganese, but do require
                                                       Culture – Principles and Practices, Vol. 23.
phosphorus, potassium and trace elements in            Developments in Aquaculture and Fisheries Sci-
the diet. Although calcium is not an essential         ence, Elsevier Science Publishers, Amsterdam,
element, a calcium:phosphorus ratio of 1:1 to          The Netherlands, 862 pp.
1:2 has been recommended. Phosphorus                McVey, J.P. (ed.) (1993) CRC Handbook of Mari-
requirement increases with the increase in             culture, Vol. I, Crustacean Aquaculture, 2nd
dietary calcium concentration. Most crus-              edn. CRC Press, Boca Raton, Florida, 526 pp.
taceans moult to grow and certain minerals          Teshima, S. (1993) Nutrition of Penaeus japonicus.
lost during this process must be replaced from         Reviews of Fisheries Science 6, 97–111.
their diet.
    Marine and freshwater shrimp farmed in          Crypts        of    Lieberkühn         Hollows
conventional ponds or tank-based systems are        between the villi with groups of undifferenti-
generally fed high quality, nutritionally com-      ated cells. These are the only cells of the villi
plete, compounded diets for the duration of         that undergo division. Renewal of the villi is
the production cycle. These feeds are usually       provided by the migration of new cells from
formulated to satisfy all of the known nutrient     the crypts towards the tip of the villi. These
requirements of the cultured species. How-          cells are among the most rapidly regenerating
ever, shrimp can also derive a substantial por-     cells of the body.                         (SB)
tion of their nutrient requirements from
                                                    Cubes         Pellets of compound feed with a
aquatic organisms produced within the culture
                                                    diameter > 15 mm. Very large pellets, nor-
system. Sinking pellets or crumbles of various
                                                    mally called rolls or cobs, tend to be used for
sizes, produced by extrusion or steam-pellet-
                                                    feeding directly on to the ground; the larger
ing processes, are widely used for feeding
                                                    size minimizes wastage and theft by birds.
shrimp at various stages of development.
                                                                                              (MG)
Water stability of feed is important because
they are slow eaters and must break the feed        See also: Compound feed; Feed blocks; Pel-
into smaller particles before ingestion. Feed       leted feed; Pelleting
attractants such as amino acids, fish extracts,
shrimp by-products, squid, clam and mussel          Curled toe paralysis            A condition of
stimulate the feeding response.                     chickens caused by riboflavin deficiency. The
    The amount of feed offered to shrimp is         chickens walk on the hocks, the toes curling
determined by the size of shrimps, stocking         under and inward. It is similar to crooked toe
density, availability of natural foods, dietary     disease, the cause of which is not known.
energy content and water quality. Daily feed                                               (WRW)
allowances may range from approximately             See also: Foot diseases; Vitamin deficiencies
25% of the body weight for larvae to less than
3% of body weight per day at market size.           Cutting date          Date of first cut of the sea-
Under laboratory conditions, feeding fre-           son will depend on the start of grass growth.
quency is reduced from six times per day for        The term includes cutting for conservation or
larvae to two or three times per day for juve-      green feeding and grazing. In intensive systems
niles to produce optimum growth and feed            the use of fertilizers and irrigation can hasten
utilization. It is important to maintain the        the start of growth, but extensive systems are
water quality at an acceptable level to produce     reliant on adequate rainfall. Ambient tempera-
a high standing crop of shrimp, therefore, the      ture must be adequate for growth.             (TS)
130                                       Cutting frequency




See also: Seasonal variation                        Cyanocobalamin: see Cobalamin

Cutting frequency          The frequency with       Cyanogenic glycosides            Cyanogenesis
which forage is cut for conservation or ‘green-     is the process by which plants release hydro-
feeding’ throughout the growing season. The         gen cyanide (HCN) from endogenous cyanide-
frequency will affect both yield (longer inter-     containing compounds. It is thought to play a
vals give higher yields) and quality (shorter       role in plant defence against generalist herbi-
intervals give higher protein and lower fibre        vores. In ruminants, hydrogen cyanide is
concentrations). In intensive systems, with         formed in the rumen and absorbed into the
adequate rainfall or irrigation, the cutting        bloodstream. A metabolite of hydrogen
cycle may be interspersed with grazing. (TS)        cyanide, thiocyanate, can be detected in urine
See also: Seasonal variation                        after 1–2 days and can be used in diagnosis.
                                                        Cyanogenic glycosides are common in
Cutting height          This depends on the         tropical fodder trees, which may make them
grass species and the cutting frequency.            unpalatable and can interfere with nutrient uti-
Longer intervals between cuts increase height,      lization. The cyanogenic glycoside, prunasin,
indicating greater maturity and, unless this is     is the toxic component in a number of browse
associated with extra leaf material, there could    species (serviceberry, Amelanchier alnifolia,
be a reduction in quality (less protein, more       and chokecherry, Prunus virginiana) and also
fibre). The chosen cutting height will reflect        in     the    eucalyptus    tree   (Eucalyptus
the need for high bulk versus high-quality          melanophloia). Drying, soaking, leaching and
material.                                   (TS)    fermentation are simple means of detoxifying
See also: Seasonal variation                        these potential feed sources. Although grasses
                                                    generally contain few intrinsic toxins,
Cyanide         An anion containing carbon          sorghum does have significant concentrations
and nitrogen, which very readily complexes          of cyanogenic glycosides. Cassava (Manihot
with ligands. A common form in nature is            esculenta) roots contain two potent
hydrogen cyanide, which dissolves in water to       cyanogenic glycosides: linamarin and lotaus-
form hydrocyanic acid. This smells of bitter        tralin. Cassava can be fed to livestock only
almonds and can be detected in the breath of        after detoxification by fermentation, boiling or
affected subjects. It is extremely toxic, causing   ensiling. Similarly, linseed contains linustatin
pulmonary failure as a result of the capacity of    and neolinustatin, which must be detoxified
the cyanide ion to bind with cytochrome oxi-        before feeding.                          (CJCP)
dase and reduce the oxygen-carrying capacity
of the cells. Cyanide also stimulates the           Cyanogens: see Cyanogenic glycosides
chemoreceptors of the carotid and aortic bod-
ies, causing hyperpnoea. Death is usually           Cyclopropenoic fatty acids               Natu-
caused by respiratory arrest, however, rather       rally occurring cyclopropenoic fatty acids,
than cardiac irregularities. Following ingestion    sterculic and malvalic acid, are found in ster-
of cyanogenic compounds, toxic symptoms             cula and cotton seeds.
appear within 1 h and so urgent treatment is
essential. Treatment is by intravenous injec-                             CH2
                                                                            \
tion of sodium nitrite, which is converted to a               CH3(CH2)7C = C(CH2)7COOH
tolerable amount of methaemoglobin that has                           Sterculic acid
a stronger affinity than cytochrome for the               8-(2-octacyclopropen-1-yl)octanoic acid
cyanide. To prevent the cyanmethaemoglobin
complex releasing cyanide, a second injection
                                                                           CH2
of sodium thiosulphate is required, which                                   \
invokes the enzyme rhodanese to convert the                   CH3(CH2)7C = C(CH2)6COOH
cyanide to the excretable thiocyanate.                                 Malvalic acid
                                          (CJCP)         7-(2-octacyclopropen-1-yl)heptanoic acid
                                              Cytokines                                            131




These compounds are potent inhibitors of ∆9          sulphate (SO42–) and the carbon skeleton
desaturase, which converts stearic to oleic          becomes pyruvate.                  (NJB)
acid. Their effect is to alter the permeability of
membranes. In laying hens, a diet containing         Cystine                           An amino acid
sterculic acid gives rise to a condition known       (COOH·NH 2 ·CH·CH 2 ·S·S·CH 2 ·CH·NH 2 ·
as pink–white disease when pink ferroproteins        COOH) found in protein. A disulphide bridge
pass from the yolk into the white. Cottonseed        within or between peptide chains can be
oil is the most important edible oil containing      formed when two cysteine groups combine.
cyclopropene fatty acids (concentration range        Following digestion (breaking of peptide
from 0.6 to 1.2%) but for human consump-             bonds), cystine or cystine-containing small
tion the oil is processed to reduce the level to     peptides are released. Cystine that exists in
0.1 to 0.5%.                               (JEM)     food proteins, particularly heat-processed pro-
                                                     teins, is less digestible (available) than either
Cysteine                         An amino acid       methionine or cysteine.
(HS·CH2·CH·NH2·COOH, molecular weight
                                                               O                              N
121.2) found in protein. It is synthesized from                         O
                                                                             S
methionine (which provides the sulphur) and
serine (which provides the carbon skeleton) in
the metabolic process known as trans-sulphu-                                 S
                                                           N
ration. Of the cysteine not used in protein                                       O           O
synthesis or catabolized (to CO2, SO42– and
                                                                                                  (DHB)
H2O), some is used for the synthesis of glu-
                                                     See also: Cysteine
tathione, some for the synthesis of taurine
and some for the synthesis of phosphoadeno-
                                                     Cystinuria (cysturia)           An inherited dis-
sine phosphosulphate. Many of the sulphydryl
                                                     ease of amino acid transport in the renal
groups of cysteine that exist in protein are
                                                     tubules. Urinary concentrations of cystine,
oxidized, with formation of a disulphide bridge
                                                     lysine, arginine, ornithine and cysteine–homo-
between two cysteine residues, forming the
                                                     cysteine-mixed disulphide are elevated.
dimeric amino acid, cystine. Cysteine (or cys-
                                                     Because of its low solubility, cystine forms cal-
tine) is capable of supplying up to 50% of
                                                     culi in the tubules leading to obstruction, infec-
dietary need for sulphur amino acids (methio-
                                                     tion and ultimately renal insufficiency.     (NJB)
nine + cysteine) of growing animals and an
even larger portion (up to 80%) of the sulphur
amino acid need of adult animals.                    Key reference
                                                     Segal, S. and Their, S.O. (1989) Cystinuria. In:
                            O                           Scriver, C.C., Beaudet, S.L., Sly, W.S. and
                                                        Valle, D. (eds) The Metabolic Basis of Inherited
                                                        Disease. McGraw-Hill, New York.
            HS
                                OH
                      NH2
                                                     Cytochrome           A class of iron-porphyrin-
                                                     containing proteins. Cytochromes are inti-
                                     (DHB)           mately associated with the respiratory chain
See also: Cystine; Glutathione; Methionine;          involved in electron transport and the oxida-
Taurine                                              tion–reduction reactions of cell respiration.
                                                     Cytochromes in the mitochondria are a direct
Cysteine dioxygenase            One of two           link to the use of molecular oxygen as a termi-
enzymes involved in the conversion of L-cys-         nal electron acceptor in aerobic metabolism
teine to pyruvate. Cysteine dioxygenase, a           leading to the production of ATP.         (NJB)
cytoplasmic enzyme, converts L-cysteine
(HSCH2·CHNH3+·COO–) to L-cysteine sulphi-            Cytokines         A family of low molecular
nate using molecular oxygen. In this process         weight (~ 30,000) proteins secreted by vari-
the sulphur atom of L-cysteine is converted to       ous cells with autocrine and paracrine actions.
132                                             Cytosine




Cytokines are involved in the coordination of         tumour cells. Still other cytokines exist and
cellular responses in various pathways includ-        more will probably be identified.        (TDC)
ing immune responses, haematopoietic cell
signalling, calcium homeostasis, skeletal mod-
                                                      Key reference
elling and remodelling, wound healing and tis-        Goldsby, R.A., Kindt, T.J. and Osborne, B.A.
sue repair, growth and ordinary replacement              (2000) Kuby Immunology, 4th edn. W.H. Free-
of aged cells. Cytokines regulate the intensity          man and Co., London.
and duration of a response by stimulating or
inhibiting activation, proliferation or differenti-   Cytosine        A pyrimidine, C4H5N3O,
ation of cells by regulating the secretion of         found in both RNA and DNA. In RNA it is
proteins or other cytokines. Cytokines include        cytidine 5 -monophosphate (CMP); when in
interleukins, interferons, colony-stimulating         DNA it is deoxycytidine 5 -monophosphate
factors and tumour necrosis factors. The              (dCMP). Cytidine is involved as cytidine
specificity of cytokines and cell response is via      diphosphate choline (CDP-choline) in phos-
specific cell surface receptors. For example,          phatidylcholine synthesis and as CDP-diacyl-
white blood cells (macrophages) and other             glycerol in phosphatidylinositol biosynthesis.
cells (activated T helper cells, TH) act by
secreting cytokines that bind receptors on the                         NH2
surface of specific cells to stimulate prolifera-
tion, differentiation or both. Interleukins may
induce pro-inflammation responses, killer cell
activation and immunoglobulin production                                       N
while interferons may prevent viral replica-
tion. At least 18 interleukins, three interferons
and two tumour necrosis factor subclasses
have been identified. The two tumour necrosis                            N            O
factors ( and ) have cytotoxic effects on                                                     (NJB)
                                              D

D value         A digestibility coefficient, usu-   into metabolizable energy (ME) using an
ally expressed in terms of the dry matter          assumed value for the gross energy of the
(DMD), organic matter (OMD) or digestible          digestible organic matter. If this is taken as
organic matter contained in the dry matter         19 MJ kg 1, ME (MJ kg–1 DM) = 0.15
(DOMD). These terms are most often used in         DOMD%.                                     (IM)
forage evaluation for ruminants and their defi-
nition needs care as they are not interchange-
able. In the UK the ‘D’ value is usually           References
                                                   Alexander, R.H. and McGowan, M. (1966) The
expressed as DOMD in practical publications
                                                       routine determination of in vitro digestibility of
while OMD or DMD are used in scientific                 organic matter in forages – an investigation of
research.                                              the problems associated with continuous large-
    DMD = dry matter digestibility                     scale operation. Journal of the British Grass-
    OMD = organic matter digestibility                 land Society 21, 140.
    DOMD = digestible organic matter con-          Tilley, J.M.A. and Terry, R.A.A. (1963) A two-
tained in the dry matter                               stage technique for the in vitro digestion of for-
where OM = organic matter = loss on com-               age crops. Journal of the British Grassland
bustion = dry matter (DM) minus ash; and               Society 18, 104.
DOM = digestible organic matter = OM in
feed minus OM in faeces.                           Dairy cattle        Bovine animals bred and
                                                   kept principally for milk production. (PCG)
        DMfed    DMfaeces
DMD =                                              Dairy products         Milk and products man-
             DMfed                                 ufactured from milk. Liquid milk is heated for
                                                   short periods of time to kill pathogens. Pas-
        OMfed    OMfaeces                          teurized milk (72°C for 15 s) can be stored for
OMD =
             OMfed                                 up to 5 days. UHT (ultra-heat-treated) milk
                                                   (132°C for 2 s) can be stored for up to 12
         OMfed     OMfaeces = OMD*%OMfood          months; sterilized milk (115–130°C for
DOMD =                                             10–30 min) can be stored for several months.
                DMfed                              Heat treatment denatures the whey proteins
    These terms can be expressed as digestibil-    in milk, giving it a boiled taste that is particu-
ity coefficients (e.g. 0.7) or as percentages       larly noticeable in UHT and sterilized milk.
(e.g. 70%). Whereas DOMD can be calculated             The butterfat contents of liquid milks are
from OMD and the OM percentage in the              3.9% (whole), 0.1% (skimmed), 1.6% (semi-
food, DMD cannot be directly calculated from       skimmed) and > 4% (Channel Islands breeds).
OMD. Digestibility determined in vivo is           In homogenized milk the fat globules are bro-
apparent digestibility, since excreta contain      ken up and remain distributed throughout the
endogenous matter. Most of these digestibility     milk so that it does not form a cream layer.
coefficients can also be applied to the two-            Cream is separated from whole milk
stage rumen-pepsin in vitro technique devised      mechanically and either sold with a fat con-
originally by Tilley and Terry (1963) and          tent between 15 and 45% or churned into
applied by Alexander and McGowan (1966).           butter. Butter manufacture produces butter-
Digestibility as D value (DOMD) can be scaled      milk as a by-product.

                                                                                                    133
134                                            Databases




   Yoghurt is made by fermenting milk with            metabolism of cysteine, glutamine, glycine,
bacteria that produce lactic acid to coagulate        histidine, methionine, serine, threonine and
the casein; sugar and fruit or flavouring may          tryptophan by specific enzymes. Ammonium
then be added.                                        nitrogen can be produced directly from glu-
   Cheese is manufactured from coagulated             tamic acid by L-glutamic dehydrogenase,
milk proteins (see Casein) and varying pro-           which links the transamination of nitrogen
portions of fat, water and salts. A general           between amino acids to nitrogen excretion.
method is to coagulate the casein to produce          Ammonium nitrogen can be incorporated into
curds and whey, cut and scald the curd, drain         urea for detoxification and excretion.   (NJB)
off the whey, press, salt and ripen the curd.         See also: Ammonia; Nitrogen metabolism
There are hundreds of varieties of cheese,
which obtain their individual characteristics by      Debeaking          Erroneous term for beak-
variations in the production process.     (PCG)       trimming, a procedure commonly used in the
                                                      poultry industry to reduce feather-pecking and
Databases         Collections of valuable mea-        cannibalism. Recent studies have shown that
surements that pertain to a specific produc-           the beak is well innervated and therefore the
tion system. The most common uses of                  practice is debatable.                 (MMax)
databases in animal production are in tables
of nutrient composition of the large range of         Decarboxylation         The removal of a
feedstuffs that may be used in animal feeds.          carboxyl carbon from a substrate with the ulti-
These data are used in feed formulation soft-         mate production of CO2. Carbon dioxide pro-
ware packages.                           (SPR)        duction by decarboxylation occurs in the
                                                      breakdown of carbohydrate-related molecules
Date         Dates are the fruit of the palm          such as pyruvate, TCA cycle intermediates
Phoenix dactylifera. When mature at 10–15             such as isocitrate and -ketoglutarate, amino
years old, date trees yield 45–90 kg of dates         acids such as glutamic acid (in the production
per tree. The leading date-producing and              of -aminobutyrate) and other amino acids (or
exporting countries are Saudi Arabia, Egypt,          related compounds) in the production of bio-
Iran and Iraq. Dates are usually grown for            genic amines.                           (NJB)
human consumption but may be fed to goats
and cattle if they fall from the tree or are of       Deer        The cervid family branched from
substandard quality. The seeds can be pressed         the ruminant stock some 30 million years
for oil, leaving a residue useful for stock feed.     ago. There are now 17 living genera, some
Date trees are drought resistant. The young           (especially Cervus) still rapidly speciating.
leaf spines are soft and the branches can be          Deer are native to all continents except Aus-
browsed or fed to cattle and goats.        (JKM)      tralasia and Africa south of the Sahara, rang-
                                                      ing from equatorial to arctic regions. They
Deamination        The process by which               occupy a wide variety of habitats, forest, open
the nitrogen from amino acids is released as          scrubland, mountain and tundra, and so their
ammonium nitrogen. This can occur by direct           natural diets and dietary adaptations vary
production of ammonium nitrogen from the              greatly (Hofmann, 1985).

Date palm nutrient composition.

                                                      Nutrient composition (g kg   1 DM)


                  Dry matter      Crude      Ether         Crude                       Starch
                   (g kg 1)       protein   extract        fibre            Ash        and sugar   NFE

Fruit             660–850          11–25     4–17          39–102           81             760      –
Fresh leaves         –            116–275   15–42          14–23          7–13              –     41–58

NFE, nitrogen-free extract.
                                                Deer                                                    135




    The social behaviour of forest species,         hay and silage, root and fruit crops, pelleted
such as roe, moose, white-tailed deer, mule         or loose concentrates, protein supplements
deer and muntjac (territoriality, small family      and mineral–urea blocks. Care should be
groups, browsing habits), makes them                taken, of course, to introduce new foods
unsuited to intensive management or                 gradually.
domestication. However, those adapted to               Deer from temperate or northern regions
more open habitats, such as red deer,               show a marked seasonality not only in their
wapiti, sika, sambar, fallow and reindeer,          reproductive cycle but also in growth and fat-
show herding behaviour and a hierarchical           tening, appetite and metabolic rate. They lay
society, mobility and versatile feeding habits,     down fat and they lactate during summer;
and recently they have been successfully            during winter, calf growth slackens and adults
domesticated as farm animals. Deer may              mobilize their fat. These cycles help to match
also be managed extensively so as to exploit        food requirement to the natural availability of
their adaptation to their natural habitat on a      forage. Both antler growth and peak milk
low-cost basis. Procedures such as disease          production occur during the summer and
control, selective culling and supplementary        place similar demands on mineral intake
feeding may then be used to increase their          (Table 3). Since food intake is naturally high
productive potential. In red deer, one adult        at this time, such mineral requirements are
stag will mate with 20–40 hinds; hinds              readily met.
remain fertile for more than 12 years; and             Deer, compared with sheep and cattle,
surplus animals may be removed for sale or          can produce an attractively lean carcass with
slaughter at 15 months of age (Blaxter et           heavy and highly priced hindquarters. This,
al., 1988). As a result, a managed herd of          together with the popular image of venison,
deer can be many times more productive              ensures a good price for deer meat, provided
than a fully wild herd.                             that it is hygienically produced and mar-
    Some typical dietary requirements for           keted, with due regard for animal welfare. As
domesticated red deer are shown in Table 1.         well-fed adults (but not yearlings) lay down
Compared with sheep, red deer have a high           substantial fat reserves by the end of sum-
metabolic rate. They also generally show a          mer, this is an unsuitable time for their
shorter retention time of food in the gut and       slaughter. Other products are antler velvet (of
so digest roughage diets a little less well. As a   supposed medicinal value), skins and soft
result their maintenance requirements are           dress leather, while the aesthetic appeal of
rather high (Kay and Staines, 1981).                these lean and agile animals serves to pro-
    In the northern hemisphere, red deer            mote tourism.                          (RNBK)
calves are born in May or June. They may
be weaned from their dam after taking
                                                    Table 1. Dietary requirements of red deer (from Adam,
colostrum and reared on a milk substitute.          1994).
This should be similar to that used for rear-
ing lambs, for deer milk is much richer than                                   Dry matter    Crude protein
cow’s milk (Table 2). Alternatively they may                                   (kg day 1)    (g kg 1 DM)
be left with their dam at pasture until             Calves
housed for the winter, or weaned at about 8           6–8 months (winter)          1.3           100
weeks of age on to a fattening diet, concen-          12–15 months (summer)        2.2         120–170
trates plus some roughage, similar to that          Hinds
used for sheep or cattle. Rapid growth and            Pregnant (winter)            2.0            100
an excellent conversion efficiency (food               Lactating (summer)           3.0            170
intake for weight gain) can be achieved             Stags
(Blaxter et al., 1988; Adam, 1994). Adult             Maintenance (winter)         3.0            100
                                                      Increasing liveweight        4.0            120
red deer will readily take a wide variety of
                                                      (summer)
foods, including forage crops and browse,
136                                                 Deficiency diseases




In the northern hemisphere, red deer calves are normally born in May or June.


Table 2. Composition of milk, mid lactation (g kg 1).

                  Crude protein (N    6.38)           Lactose      Fat      Ash    Dry matter   Energy (kJ kg 1)

Red deer                     75                         45         100       11       230            6500
Dairy cow                    35                         48          35        9       130            2900



Table 3. Minerals (g) deposited in antlers by a 125 kg             Society    of    New    Zealand,  Wellington,
red deer stag, and secreted in milk by a 80 kg red deer            pp. 393–407.
hind during full lactation (Kay and Staines, 1981) and          Kay, R.N.B. and Staines, B.W. (1981) The Nutri-
recommended dietary content (Adam, 1994).                          tion of the Red Deer. Commonwealth Agricul-
                                                                   tural Bureaux, Slough, UK.
                                     Ca       P       Mg        Wemmer, C.M. (ed.) (1982) Biology and Manage-
Antlers                              350      160      5           ment of the Cervidae. Smithsonian Institution
Milk                                 370      300     20           Press, Washington, DC.
Recommended dietary content          3–6      2–4     1–2
  (g kg 1 DM)
                                                                Deficiency diseases            A deficiency nor-
                                                                mally refers to an inadequate supply of one or
References and further reading                                  more specific nutrients, rather than a general
Adam, C.L. (1994) Feeding. In: Alexander, T.L.                  restriction of intake or a deficiency in any
   and Buxton, D. (eds) Management and Dis-                     other aspects of an animal’s environment.
   eases of Deer. The Veterinary Deer Society,                  There are seven major classes of nutrients –
   London, pp. 44–54.                                           protein, carbohydrate, minerals, vitamins,
Blaxter, K., Kay, R.N.B., Sharman, G.A.M., Cun-
                                                                lipids, fibre and water – a deficiency of any of
   ningham, J.M.M., Eadie, J. and Hamilton, W.J.
                                                                which can cause characteristic disease symp-
   (1988) Farming the Red Deer. HMSO, Edin-
   burgh.                                                       toms, such as iron deficiency causing
Hofmann, R.R. (1985) Digestive physiology of the                anaemia. Some deficiencies cause asympto-
   deer – their morphological specialisation and                matic disorders that reduce vigour, activity and
   adaptation. In: Fennessy, P.F. and Drew, K.R.                production in farm animals, e.g. restrictions in
   (eds) Biology of Deer Production. The Royal                  energy or sodium intake.
                                         Deficiency diseases                                      137




    The severity of a nutrient deficiency will        minor or trace nutrients often depends on the
depend on an animal’s requirement, so that a         intake of other nutrients. Some may have
cow in early lactation may be deficient in            generic effects that influence the availability of
energy when offered a diet with an energy den-       several elements, such as the effect of ascor-
sity that would be adequate for a non-               bic acid on the availability of many heavy met-
lactating cow. A deficiency becomes a disease         als, particularly iron, or the adverse effect on
when the welfare of the animal is reduced by         the immune system of selenium or vitamin E
the nutrient deficit. Thus, depending on how          deficiencies. Others rely on the similarity in
welfare is defined, an animal either fails to cope    the chemical properties of different elements
with the deficiency or feels unwell as a result. In   for their interdependency, e.g. cadmium and
many circumstances the deficiency is tempo-           sodium, or the formation of stable complexes
rary, until homeostatic mechanisms are               in the digestive tract, e.g. copper thiomolyb-
employed that allow the animal to cope. These        dates in ruminants.
may be by increasing the absorption of the               Samples that can be taken from farm ani-
deficient nutrient or by reducing output, e.g. of     mals to diagnose a deficiency include blood
milk. Even if they are only temporary, diseases      plasma, saliva, faeces or urine. Occasionally
would normally exist for several days, or regu-      tissue biopsies (e.g. liver) are performed for
larly for a period of each day, to be classified as   diagnostic purposes. Occasionally hair, hoof
such. Theoretically deficiencies can only exist       and other tissues are sampled to give a histori-
for elements or compounds that are required          cal record of the progression of the deficiency.
by the animal, but in recent years an essential-         Another aid to diagnosis of a deficiency dis-
ity has been demonstrated for many elements          ease is the animal’s behaviour. Many animals
that were not previously believed to be required     that are short of specific nutrients develop an
by animals, even though it has not so far been       opportunistic appetite to try to obtain the
possible to quantify the requirement.                nutrient in deficit. This has been demonstrated
    The severity of the deficiency is mainly          for many species whose members are short of
determined by the animal’s capacity to store         sodium, for chickens that are short of calcium
the element and the fluctuation in intake.            and for cattle that are deficient in phosphorus.
Fluctuations in intake may arise from a vari-        Sometimes the novel appetite is focused on
able food supply in farm animals foraging on         learnt methods of obtaining the nutrient in
rough grazing or from a deliberate restriction       deficit; for example, animals with sodium defi-
of intake for economic reasons. Towards the          ciencies lick each other’s skin to get salts.
end of winter, the availability of feed may be           As agriculture has developed in recent
deliberately restricted by farmers in anticipa-      years, some nutrients have become routinely
tion of the growth of grass in spring. Food          deficient in farm animals. For example, the
availability and intake may also fluctuate with       milk yields of dairy cows have increased con-
the physiological state of animals; for exam-        siderably, leading to a significant likelihood
ple, dry sows might be restricted to prevent         that the cow will be deficient in calcium in the
them from becoming obese. Storage organs,            first week of lactation. After a few days, it is
such as the liver for copper and zinc, or the        able to mobilize the necessary calcium from
bones for calcium, may accumulate toxic ele-         bones and a clinical disorder is usually avoided.
ments in place of essential ones, such as cad-       Farmers now often prepare cows for the cal-
mium being stored in the liver and lead in           cium demands of early lactation by feeding
bones, exacerbating or perhaps even trigger-         them a calcium-deficient diet for up to 1
ing a deficiency in the essential element.            month before parturition. This entrains the cal-
    If clinical symptoms are evident, the aetiol-    cium mobilization pathways in advance of the
ogy of a deficiency disease can usually be            period of increased requirements. Another
traced to the nutrient in deficit. However, some      example is the deficiency in sodium intake,
farm animals, such as cattle and sheep, having       which arises when large quantities of potas-
evolved from prey species, do not show overt         sium are used on pasture to stimulate grass
signs of pain and so diagnosis can be difficult.      growth. Potassium in soil is antagonistic to
    The animal’s status with regard to many          sodium uptake by plants, and potassium in the
138                                           Dehull




rumen is antagonistic to magnesium absorp-         Dehydration, body            A state in which
tion. This leads to both sodium deficiency,         the body is in negative water balance, i.e.
which is easily rectified by salt supplements or    when it loses more water than is ingested as
sodium fertilizers, and magnesium deficiency,       liquid and in food. It may arise from either
which is not so easily rectified. Magnesium         insufficient intake of water or excessive loss,
deficiency, or hypomagnesaemia, can some-           e.g. from diarrhoea and vomiting, beyond the
times be rectified by adding magnesium salts to     ability of the kidneys to compensate. The ini-
the drinking water or feed, or by broadcasting     tial response of the body to negative water
calcined magnesite on the pasture, but none of     balance is the withdrawal of water from the
these mechanisms ensures adequate magne-           interstitial fluid space in an attempt to main-
sium intake by cattle. As the onset of the dis-    tain normal blood volume. Connective tissue,
ease is sudden, unlike sodium deficiency, the       muscle and skin are most affected, leading to
mortality rate is high. Herbivores have an         the clinical test of prolonged elevation of a
acute appetite for sodium, unlike magnesium        skin fold. More advanced dehydration results
and calcium, which suggests that sodium defi-       in a reduction in blood volume, accompanied
ciencies have been common throughout their         by haemoconcentration. Milk yield is
evolution and indeed they are still observed in    depressed in lactating animals. In order to
wild cattle in Southeast Asia.                     produce more metabolic water, there is an
    Calves reared on milk-based diets for veal     increase in the oxidation of fat, then of carbo-
production may routinely suffer from iron          hydrate and finally of protein. Dehydration
deficiency, manifested as anaemia, because          can contribute to death, especially when com-
the milk has a low supply of iron. The conse-      bined with another clinical condition, e.g. an
quences for the animal – lethargy and fatigue      electrolyte imbalance.
– are not likely to affect the animal’s survival       Racehorses and eventer horses can easily
adversely and may even increase feed conver-       become dehydrated, since they lose large
sion efficiency. However, deficiencies that          quantities of hypotonic sweat when exercised,
result from an unsuitable farming system are       especially under hot conditions. Because of
now increasingly believed by the public to be      the conflicting stimuli regulating the secretion
unacceptable, and in the European Union            of renin and angiotensin II, such horses may
minimum iron levels in blood are now legally       refuse to drink to correct the resultant dehy-
established. Suckling piglets are also prone to    dration.                                  (ADC)
iron deficiency and are routinely given an iron
injection soon after birth.                        Dehydroascorbate            The oxidized form
    Some elements, such as selenium and            of L-ascorbate (L-ascorbate   L-dehydroascor-
iodine, can be given to farm animals so that       bate      2H). It is produced when ascorbate
their products are rich in these elements and      participates in oxidation–reduction reactions
human consumers will be more likely to             in cellular metabolism.                 (NJB)
obtain an adequate supply. An increasingly         See also: Ascorbic acid
important area of research is the extent to
which genetic differences in absorption pro-       Dehydrogenase             A class of enzymes
voke deficiency diseases. The differences have      involved in metabolic oxidation–reduction
been identified in the absorption of copper,        reactions. They act by removing hydrogen
but a better understanding of mineral absorp-      from a substrate or adding hydrogen to a sub-
tion is needed before genetic differences can      strate. These enzymes cannot use oxygen as
be exploited in practice.                (CJCP)    the acceptor but instead use one of three
                                                   coenzyme        combinations:     NAD/NADH,
Dehull        To remove the kernel coat or         NADP/NADPH, FAD/FADH. These co-
pericarp of a seed.                 (JMW)          enzymes link metabolic oxidation to the electron
                                                   transport chain (a series of dehydrogenases
Dehydration         A deficit of water in the       involved in oxidation–reduction steps carried out
body. Dehydration may result from a lack of        by cytochromes) and link substrate oxidation
drinking water, excessive evaporative loss or      with molecular oxygen as the terminal electron
diarrhoea.                             (JMW)       acceptor, yielding water.                   (NJB)
                                          Detoxification                                        139




Demand feeding          Spontaneous feeding        See also: Carbohydrates; Deoxyribonucleic
‘on demand’, or ad libitum, when food avail-       acid (DNA); Monosaccharide
ability is unlimited.                 (JSav)
                                                   Depigmentation            A pigmentation dis-
Deoxynivalenol               Deoxynivalenol        order of the skin, mucous membranes, hair,
(DON) or vomitoxin is a mycotoxin of the tri-      or retina in which melanocytes in these tissues
chothecene class, produced by Fusarium             are affected or destroyed. The brown pigment
fungi. DON causes feed refusal and vomiting        melanin is produced from the amino acid
in swine, and feed refusal and oesophageal         tyrosine by specialized pigment cells called
lesions in poultry. Trichothecenes such as         melanocytes. Copper deficiency causes depig-
DON tend to be produced in moist grain             mentation of hair, fur, wool and feathers in
under cool or cold environmental conditions.       animals. Depigmentation may also develop
Wheat and maize are the grains most com-           due to hyperthyroidism, adrenocortical insuffi-
monly contaminated by DON.              (PC)       ciency, alopecia, anaemia, certain infectious
                                                   diseases, excessive sun exposure or albinism
Deoxyribonuclease          An enzyme, also
                                                   in humans and other animals.              (SPL)
called DNase, hydrolysing deoxyribonucleic
acid (DNA) into nucleotides. A DNase (DNase        Desmosine          A unique structure of cross-
I; deoxyribonucleate 5 -oligonucleotidohydro-      linked lysine, found only in mature elastin. In
lase; EC 3.1.21.1) is purified from pancreatic      the biosynthesis of elastin, three lysine
secretions. Another DNase II is purified from
                                                   residues are oxidized by the enzyme lysyl oxi-
the spleen.                              (SB)
                                                   dase; these combine with a fourth lysine to
                                                   form the cross-linked structure of desmosine.
Deoxyribonucleic acid (DNA)             A poly-
                                                   Desmosine stabilizes the structure of elastin,
mer of deoxyribonucleotides, each consisting of
                                                   which contributes to connective tissues its
a sugar, deoxyribose, and a nitrogenous base,
which is derived from one of two purines, ade-     properties of extensibility and elastic recoil.
nine or guanine, and one of two pyrimidines,                                                   (NJB)
thymidine or cytosine. DNA can be considered       Desoxysugar: see Deoxysugar
the chemical basis of heredity: the genetic code
is the sequence of deoxynucleotides found in       Detoxification          A process by which a
the genes that make up chromosomes. DNA is         toxin is changed to a less toxic compound or
made up of two complementary strands in the        by which its poisonous effect is reduced. In
form of an -helix. The genetic code is given       ruminants, rumen microbes are the first line
by the sequence of deoxynucleotides in DNA,        of active defence against some plant toxins,
each amino acid being represented by a spe-        e.g. ricin in castor bean, mimosine in Leu-
cific set of three. This code is transcribed to     caena, nitrotoxins in Astragalus, nitrates in
messenger RNA, which specifies the complete         many forage plants, oxalates in Halogeton,
amino acid sequence of the protein being syn-      phyto-oestrogens in clovers, pyrrolizidine alka-
thesized.                                  (NJB)   loids in Senecio and Heliotropium, thiami-
                                                   nase in bracken fern and many mycotoxins.
Deoxysugar          A monosaccharide contain-      Once absorbed, some toxins can be detoxified
ing less oxygen than the parent sugar. Usually,    by enzymes in the gut and intestinal lining,
the terminal –CH2OH group is replaced by a         liver, lungs and kidney.
–CH3 group. In bacteria, more than one                 There are antidotes for a few specific plant
hydroxyl group may be replaced with hydrogen,      poisons. Bracken fern poisoning can be
producing di- and tri-deoxysugars. The most        treated by butyl alcohol in cattle or by thi-
abundant deoxy sugar in nature is 2-deoxy-D-       amine in horses, fluoroacetate poisoning by
ribose, the sugar component of deoxyribonu-        glyceryl monoacetate and pentobarbital,
cleic acid. Bacterial lipopolysaccharides can      hydrocyanic acid poisoning by nitrite or thio-
contain L-rhamnose (6-deoxy-L-mannose) and L-      sulphate, nitrates and nitrotoxin poisoning by
fucose (6-deoxy-L-galactose).           (JAM)      methylene blue or ascorbic acid, oxalate poi-
140                                         Deuterium




soning by calcium hydroxide or calcium glu-        sequent glycosuria as a result of insufficient
conate, Jimson weed poisoning by neostig-          pancreatic production of insulin or impaired
mine      and       larkspur    poisoning    by    response of its tissue receptors to a normal
physostigmine. Potassium permanganate and          circulating level of insulin. Refined sugars in
tannic acid will bind to many alkaloids.           the diet should be replaced by fibre-rich foods
    Compounds that bind toxins may also be         containing unrefined carbohydrate; the pro-
given. Activated charcoal binds to many tox-       tein content should remain normal but the fat
ins in the gastrointestinal system; clay miner-    content should be reduced, especially if the
als and aluminosilicates also bind molecules of    animal is overweight.                   (ADC)
certain sizes and configurations. Cyclodextrins
are oligomers of glucose with cylindrical          Diaminopimelic acid           An amino acid,
hydrophobic        cavities   surrounded     by    H2N·CH·(COOH)·(CH 2)3·CH·(COOH)·NH 2,
hydrophilic margins that encapsulate certain       (DAPA) found in the peptidoglycan of all
small toxins, such as corynetoxins in annual       Gram-negative and some Gram-positive bac-
ryegrass (Lolium rigidum).                         teria, but not Archaea. In Gram-negative bac-
    Vaccines against low-molecular-weight tox-     teria, the peptidoglycan is 10% of the cell
ins are difficult to create. However, there has     wall, while in Gram-positive bacteria it is
been some success in developing a vaccine          90%. It has been used to estimate bacterial
against phomopsin mycotoxins that cause            biomass outflow from the rumen and the frac-
lupinosis, corynetoxins in annual ryegrass and     tion of faecal matter attributed to bacteria.
ergot alkaloids in tall fescue. Vaccines against   However, the ratio of DAPA to cell biomass is
other toxins are being developed.         (MHR)    highly variable.                       (DMS)

Deuterium          A stable isotope of hydro-      Diammonium phosphate                   Dibasic
gen. It has one neutron and one proton and is      ammonium phosphate, (NH4)2HPO4, is typi-
twice as heavy as hydrogen (2.014 vs.              cally manufactured by the acidification of rock
1.008). Its physical and chemical properties       phosphate to produce phosphoric acid, which
are very similar to those of hydrogen. It is       is in turn mixed with ammonia and heated
used as a non-radioactive tracer in studies of     under pressure. Manipulation of temperature
the molecular metabolism of carbohydrates,         and pressure determines whether a mono- or
fatty acids and amino acids. As a tracer in        dibasic salt is produced. The dibasic salt is
water (2H2O) it is used to measure total body      extremely unpalatable and is rarely used in
water and body water turnover. As doubly           animal feeding stuffs. Consequently, most of
labelled water (2H218O) it is used to estimate     the material that does come on to the market
CO2 production and (by assuming a respira-         is unrefined and the level of contamination
tory quotient) the heat production or energy       usually prevents it from reaching feed grade
expenditure of free-ranging animals.     (NJB)     standard.                               (CRL)

Development: see Growth; Growth factors            Diarrhoea          The major cause of diar-
                                                   rhoea is a local irritation of the intestinal
Dextrins          -Glucosidic chains of varying    mucosa by infectious or chemical agents,
length, but with a lower average molecular         which often leads to an increased flow of
weight than starch, soluble in water but insolu-   intestinal secretions, distension of the lumen
ble in alcohol and ether. They are intermedi-      and a consequent increase in motility.
ate products of starch hydrolysis.        (NJB)    Dietary diarrhoea occurs in all species and at
                                                   all ages but is most common in neonatal ani-
Diabetes         A condition characterized by      mals ingesting more milk than can be
polyuria and polydypsia. There are two sepa-       digested, perhaps resulting in secondary col-
rate disorders. Diabetes insipidus is caused       ibacillosis and salmonellosis. Feeding inferior
either by insufficient production of antidiuretic   quality milk replacer to young calves is also a
hormone or by failure of its receptor in the       very common cause of dietary diarrhoea.
renal collecting ducts. Diabetes mellitus is       Heat denaturation during the preparation of
associated with hyperglycaemia and the con-        milk replacers can result in a decrease in the
                                            Dietary fibre                                        141




concentration of non-casein proteins, leading       Dicarboxylic acids        Organic acids con-
to poor clotting in the abomasum and thus           taining two ·COOH groups. Examples in
reduced digestibility. The use of excessive         metabolism are oxalate ( OOC·COO ), succi-
amounts of carbohydrates and proteins that          nate ( OOC·CH2·CH2·COO ), fumarate
are not derived from milk also predisposes to       ( OOC·CH=CH·COO ) and oxaloacetate
diarrhoea in calves, as does the inclusion of       ( OOC·CH2·C=O·COO ).              Aspartate
too much protein from soybean or fish. The           ( OOC·CH2·CHNH3·COO ) and glutamate
proteases in the digestive tract of pre-rumi-       ( OOC·H2·CH2·CHNH3·COO ) are dicarb-
nant calves and lambs cannot denature the           oxylic amino acids.                    (NJB)
soluble antigenic constituents of soybean
protein and so a hypersensitive reaction may        Dicoumarol (coumarin)            White and yel-
develop in the tract of such animals. Simi-         low sweet clover (Melilotus albus and M. offic-
larly, milk replacers made from components          inalis) are biennial legumes that grow
of bovine origin may lead to diarrhoea when         throughout much of the USA. The plant’s
fed to lambs, piglets or foals.                     pleasant odour is due to coumarin, a non-toxic
    Dietary diarrhoea can be induced in all         substance that is converted to the anticoagulant
species by a sudden change in diet, particu-        dicoumarol when moulds grow on clover hay
larly at the time of weaning. This is particu-      or silage. Dicoumarol is a vitamin K antagonist
larly important in the early-weaned pig. The        and animals poisoned by it lack the critical pro-
cause is probably related to the fact that          teins needed for blood coagulation. Affected
changes in gut enzyme activity, necessary for       animals bruise easily and bleed excessively.
the digestion of a new diet, take some time,        Some may bleed to death from a relatively
so that gradual exposure to the new diet is         small injury or surgery such as castration,
advisable to maintain proper digestion.             dehorning, or vaccination. Prevention lies in
    Treatment of dietary diarrhoea in the           avoiding mouldy feeds or limiting the dose by
neonate involves cessation of milk-feeding for      intermittently feeding only small amounts of
24 h and its replacement by oral electrolyte        affected clover hay or silage.              (LFJ)
solutions. Milk of the correct composition is
then gradually reintroduced. Treatment with         Diet       All food consumed over a specified
an antibiotic may be necessary if secondary         period. The term includes any material that
infection is suspected, along with oral kaolin      enters the digestive tract, regardless of
or pectin to protect damaged intestinal             whether or not it is nutritionally available. It
mucosa.                                 (ADC)       can be applied to a single feed or a combina-
                                                    tion of feeds, e.g. roughage and concentrate
Diastase        An    obsolete   synonym      for   fed to ruminant animals.                 (SPR)
amylase.                                    (SB)
                                                    Diet-induced thermogenesis: see Heat
Dicalcium phosphate             Dibasic calcium     increment of feeding
phosphate is usually available in anhydrous
(CaHPO4) or dihydrate (CaHPO4.2H2O)                 Dietary fibre          Dietary fibre is the name
forms. The phosphorus (P) occurs in the             given to the polysaccharides of plants that can-
highly available ortho (PO43–) form. The crys-      not be hydrolysed by the digestive enzymes of
talline product is usually prepared by the treat-   higher animals. It includes cellulose, hemicellu-
ment of rock phosphate with hydrochloric            loses, pectic substances, fructans and -glu-
acid. Acid treatment of bones or heat defluori-      cans. Lignin, a group of complex polyphenolic
nation of rock phosphate are alternative            compounds, is usually also included. The
methods of production. Pure anhydrous dical-        dietary fibre complex is the major source of
cium phosphate contains 22.8% P by weight           energy via fermentation in ruminants and a
but, depending on the origin and method of          minor source in non-ruminant species. Fer-
production, the actual level is usually between     mentation yields short-chain fatty acids,
18% and 20.5%. The corresponding value for          acetate, propionate, butyrate and lactic acid,
the dihydrate is 17% to 18%.              (CRL)     carbon dioxide, methane and hydrogen. An
See also: Rock phosphate                            estimated 400–600 different bacterial strains
142                                          Dietary fibre




produce enzymes that degrade these carbohy-          gravimetric method that is widely applied to ani-
drates. Typically, 60–80% of the energy and          mal feeds. It was designed to recover plant cell
two-thirds of the amino acids needed daily by        wall material and does not recover storage or
adult ruminants are produced by the microbial        soluble fibre components, though a modification
fermentation. If starch is present in the diet of    of the NDF method allows recovery of a soluble
the ruminant, it is typically fermented in the       fibre fraction (Mongeau and Brassard, 1993).
rumen, whereas in non-ruminants it is digested       The NDF method measures all cellulose, vari-
in the stomach and small intestine. Variable         able amounts of the hemicelluloses and essen-
amounts of starch, particularly in legumes and       tially no pectins or         -glucans. Enzymatic
severely treated grains, are not susceptible to      treatment with amylase is necessary to remove
endogenous enzymes in non-ruminants: this            starch from the NDF residue (Robertson and
fraction of starch is termed resistant starch. It    Van Soest, 1981). Nitrogen also is incompletely
passes into the large intestine where it is          removed by conventional NDF analysis. In the
rapidly and completely fermented.                    Association of Official Analytical Chemists
    The rate and extent of fermentation of the       (AOAC) method, a dry sample is defatted (if it
dietary fibre polysaccharides are determined by       contains more than 5% by weight of fat),
physical and biochemical characteristics of the      treated with proteases and amylases, dried and
plant material. If there is extensive lignifica-      weighed. Then one aliquot of the remaining
tion, microbial action is hindered and fermen-       fibre residue is ashed; Kjeldahl nitrogen is mea-
tation of the material is incomplete before it       sured in the duplicate aliquot and converted to
leaves the rumen. The extent of silicification        crude protein ( 6.25). The weights of ash and
and cutinization also affects microbial fibre         crude protein are subtracted from the residue
degradation. Tannins, essential oils and             weight to give total fibre. The AOAC method is
polyphenols, if present, inhibit cellulases and      not without potential error – firstly because
proteases and slow rumen digestion. Solubility       starch is not always removed completely and
also determines fermentation rate. Soluble           secondly because, during the ethanol precipita-
dietary fibre in forages includes unlignified pec-     tion step, simple sugars co-precipitate with the
tic substances and hemicelluloses, -glucans          fibre residue when they are present in high con-
and fructans. Soluble carbohydrates are rapidly      centrations, such as in fruits or feeds containing
                                                     sugar products. Both sources of error produce
and completely fermented both in the rumen
                                                     an inflated dietary fibre value. The most accu-
and in the large intestine of non-ruminants.
                                                     rate method of measuring dietary fibre is to
Structural carbohydrates in plants include cellu-
                                                     obtain a residue free of simple sugars and
lose, hemicelluloses and pectins. They may be
                                                     starch, acid-hydrolyse it with sulphuric acid to
associated with lignin. These components are
                                                     generate the constituent monosaccharides and
generally more extensively fermented in the
                                                     individually quantitate these, usually by either
rumen than in the large intestine of non-rumi-
                                                     HPLC or GLC. Colorimetric quantitation of
nants. For example, wood and newsprint are
                                                     these mixtures of monosaccharides is not accu-
not degraded in non-ruminants, whereas in the
                                                     rate because the mixture contains essentially
rumen 0–40% of wood and about a quarter of           unknown amounts of different monosaccharides
newsprint is fermented. Straw, cottonseed            which absorb at different wavelengths. All fibre
hulls and tropical grasses are either not fer-       analysis methods are labour intensive and
mented or poorly fermented in the large intes-       require considerable analytical expertise to
tine of non-ruminants, but one-third to              obtain accurate or even reproducible results on
two-thirds of them is fermented in the rumen.        a variety of samples.                       (JAM)
    Dietary fibre is analysed essentially by remov-   See also: Carbohydrates; Gums; Hemicellu-
ing all of the non-fibre components from the          loses; Oligosaccharides; Pectic substances;
plant material. However, many methods of fibre        Pentosans; Storage polysaccharides; Struc-
analysis either do not remove non-fibre compo-        tural polysaccharides
nents adequately or fail to recover completely
material that is a part of the dietary fibre com-     References
plex. The neutral detergent fibre (NDF) proce-        Mongeau, R. and Brassard, R. (1993) Enzymatic-
dure (Van Soest and Wine, 1967) is a                   gravimetric determination in foods of dietary
                                              Digestibility                                        143




   fiber as sum of insoluble and soluble fiber frac-    in ruminants; addition of feed enzymes, such as
   tions: summary of collaborative study. Journal     glucanase and arabinoxylase, can reduce viscos-
   of the Association of Official Analytical           ity in the small intestine of poultry and piglets.
   Chemists 76, 923–925.                              All these treatments improve digestibility. Food
Robertson, J.B. and Van Soest, P.J. (1981) The
                                                      processing may have a negative influence, in
   detergent system of analysis and its application
   to human foods. In: James, W.P.T. and Thean-       particular on the digestibility of proteins. Heat
   der, O. (eds) The Analysis of Dietary Fiber in     causes the formation of inter- and intramolecu-
   Food. Marcel Dekker, New York, pp. 123–158.        lar covalent bonds that are resistant to enzy-
Van Soest, P.J. and Wine, R.H. (1967) Use of          matic digestion. In the presence of reducing
   detergents in the analysis of fibrous feeds. IV.    sugars (e.g. fructose) and amino acids, the Mail-
   Determination of plant wall constituents. Jour-    lard reaction leads to the formation of com-
   nal of the Association of Official Analytical       plex adducts between the sugar and amino
   Chemists 46, 829–825.                              acids, especially lysine. The Maillard reaction
Diffusion          A process of molecular mix-        can also occur during storage of dried foods and
ing of gases or liquids when pure substances          make lysine unavailable for absorption.
are either poured together or are separated by            Starch is generally made more available by
a semipermeable membrane and allowed to               heat processing but this can also convert avail-
mix. In a cellular setting gases and substrates       able starch into a form that is unavailable for
diffuse down electrochemical gradients across         enzymatic degradation. Resistant starch is
membranes by either simple diffusion (no car-         produced by rearrangements in the molecular
rier) or facilitated diffusion, where a carrier       structure of amylose, which constitutes about
protein is involved.                     (NJB)        20% of starch and is generally less available
                                                      than amylopectin.
Digesta        The contents of the digestive              The digestibility of a nutrient is not a con-
tract, synonymous with chyme. Digesta con-            stant value, like a chemical analysis of the
sist of undigested feed mixed with secretions,        nutrient in a particular sample of feed. Feeding
desquamated mucosal cells and microorgan-             conditions (e.g. method and level of feeding)
isms.                                     (SB)        and the particular animal (its species, sex, age
                                                      and physiological stage) influence digestibility.
Digestibility           A measure of the degree of        The digestibility of a nutrient after passing
net absorption in the digestive tract of dietary      through the entire digestive tract can be deter-
nutrients. Macromolecules such as starch and          mined by total collection of faeces over a suit-
proteins need to be degraded to absorbable            able period. Digestibility measured directly
units, i.e. monosaccharides and amino acids.          from the difference between the intake (I) and
This is done by the digestive enzymes of the          output in digesta or faeces (O) of the nutrient
animal as well as those of gastrointestinal           is called the apparent or net digestibility (AD):
microflora. In carnivores and omnivores, the                            AD (I O) / I
animal’s own enzymes predominate, whereas in          However, the excreted matter also includes
non-ruminant herbivores microbial activity usu-       the endogenous loss of the particular nutrient,
ally predominates. Microbial activity in the          which has been digested and absorbed but has
rumen converts food nutrients into microbial          then re-entered the gut in the form of endoge-
matter and volatile fatty acids, both of which are    nous secretions. After correction for this loss
then utilized by the host animal.                     (E), the true digestibility (TD) of the dietary
    Digestibility is influenced by a number of fac-    nutrient can be calculated:
tors relating to treatments of the foodstuffs and                    TD (I O E) / I
complete diets, e.g. milling and processing. Pro-         The endogenous losses of a nutrient were
cessing can improve digestibility; for example,       traditionally estimated by measurements of the
heat can destroy antinutritional factors such as      losses in animals given diets devoid of that
protease inhibitors in legume seeds and thereby       nutrient. However, for some nutrients at least,
reduce endogenous protein losses; chemicals           endogenous secretions may be modified by the
such as sodium hydroxide can make lignified            diet and these estimates may not represent
cellulose more available for microbial enzymes        what occurs under normal circumstances, when
144                                           Digestibility




the animal eats a complete diet. For this rea-        more, an ideal marker must not be absorbed
son, other corrections are used. Undigested           and affected by the digestive tract or the micro-
food and unreabsorbed endogenous secretions           bial population in the tract and it should be
may, furthermore, be metabolized by the               closely associated with or physically similar to
microflora, being either degraded or converted         the undigested nutrient in question. No existing
to microbial matter. In non-ruminants, micro-         marker totally satisfies all these requirements.
bial metabolism occurs predominantly in the           The combined use of internal and external
large intestine. The digestibility of protein and     markers can improve the measurements, e.g.
amino acids is particularly influenced by micro-       insoluble ash can be used as an internal marker
bial metabolism. Most of the protein in faeces        together with chromic oxide, one of the most
is microbial, and because the microflora can           commonly used external markers.
synthesize amino acids there may be little rela-           To determine the digestibility of nutrients that
tion between the amino acid composition of            are modified in the large intestine, especially
the undigested food and that of the faeces. This      amino acids, digesta are sampled at the terminal
in turn means that digestibility of amino acids       ileum to determine ‘ileal digestibility’. The sim-
measured over the entire digestive tract may be       plest method of obtaining samples of digesta
very misleading. Lipids are less metabolized by       from the terminal ileum is to sacrifice the ani-
the intestinal microflora but fatty acids can be       mals, taking the samples under terminal anaes-
elongated and unsaturated fatty acids may be          thesia. For repeated sampling, various kinds of
partly hydrogenated by the microbial metabo-          cannula may be used. A simple T-cannula allows
lism in the large intestine. Carbohydrates not        only partial sampling and needs the inclusion in
available for digestion in the small intestine, due   the diet of an indigestible marker. The cannula is
to either physical inaccessibility or chemical        relatively small and may give unrepresentative
structures not hydrolysed by the mammalian            samples with coarse or fibre-rich feeds. A more
enzymes (in dietary fibre), are the main energy        advanced technique, the post-valvular ileocaecal
sources for the microflora. The end-products of        cannula, involves a large cannula placed in the
microbial fermentation, i.e. the short-chain          caecum opposite the ileocaecal valve. It can be
fatty acids, are absorbed by the host animal and      steered with a nylon cord in such a way that,
contribute to the energy supply.                      during the collection, digesta are directed into
    A complete characterization of nutrient           the cannula, so that, during the sampling period,
availability in the animal therefore includes         all the digesta leaving the ileum are collected. An
measurements of digestibility in the different        alternative surgical approach, which avoids the
compartments of the gastrointestinal tract, i.e.      use of a cannula, is to bypass the large intestine
in non-ruminants, of digesta at both the ileal        by ileorectal anastomosis.
and faecal level, respectively. In ruminants,              In fish, digestibility is measured by several
measurements of degradation in the rumen are          methods for faeces collection, including dis-
of particular importance, due to a relatively         section, stripping (i.e. pressing digesta out of
predictable and constant composition of the           the rectum with the fingers) or anal suction of
outflow from the rumen. In animals with a less         the individual fish, or alternatively, immediate
significant microbial activity, e.g. carnivores        pipetting, continuous filtration, or decanting
such as mink, ileal sampling is of less impor-        of tank water.
tance for a proper characterization of                     By the use of marker technique, the deter-
digestibility.                                        mination of digestibility is based on the
    Sampling of digesta for measurements of           increase of the marker in relation to the nutri-
digestibility in different compartments requires      ent in the digesta or faeces. AD is calculated
a cannula. If only a fraction of digesta is col-      from analyses of the concentrations (g kg 1)
lected, an indigestible marker must be added          of nutrient (N) and marker (M) in the experi-
to the diet so that the proportion of the whole       mental diet and in samples of digesta (or fae-
flow that is collected can be calculated. For a        ces), n and m, respectively.
correct measurement of the digestibility of a                      AD (N n.(M/m)) / N
nutrient, the flow rate of the marker needs to              Other     approaches       to     determining
be the same as that of the nutrient. Further-         digestibility are based on: (i) the rate of
                                              Digestion                                             145




appearance of the nutrient in the body by            both the energy value of a diet and the energy
measuring the difference in the arteriovenous        requirements of animals.              (JAMcL)
concentration across the portal-drained vis-         See also: Energy balance
cera together with the portal blood flow; this
approach may underestimate absorption due            Digestible organic matter: see D value
to uptake of the nutrient by the tissue of the
gut; (ii) isotopic techniques, e.g. labelling the    Digestion          The process of breaking down
experimental animal with 15N so as to distin-        dietary components to make them available for
guish (labelled) endogenous protein from             absorption from the gastrointestinal lumen by
(unlabelled) dietary protein; this gives a direct    epithelial cells. Food particles are reduced in size
measure of the real digestibility of dietary pro-    by mechanical and chemical means. The
tein, uninfluenced by endogenous protein              mechanical breakdown is performed by chew-
loss; however, there may be some recycling of        ing in the mouth and by contractions of the
(unlabelled) nutrient from the diet into endoge-     muscular walls of the gastrointestinal tract.
nous secretions during the feeding period; and       Chemical breakdown is mainly effected by
(iii) chemical modification of the dietary pro-       enzymes secreted in digestive juices. Food con-
tein, e.g. treatment with o-methyl-isourea in        stituents of large molecular weight, such as pro-
order to guanidinate lysine to homoarginine          teins, starch and lipids, have to be broken down
and then to determine lysine digestibility; this     to low-molecular-weight compounds before they
method assumes that the chemical reaction is         can be absorbed. A large number of specific
distributed equally between digestible and indi-     enzymes are involved in their breakdown, some
gestible lysine, that the treatment does not         from the animal and some from colonizing
influence the general digestibility of the pro-       microorganisms in the digestive tract.
tein, and that homoarginine is digested and              Most digestive enzymes are found in all
absorbed to the same extent as lysine.               species. However, their activity varies with age
     Other methods include predictions from: (i)     and responds to variations in the diet. The
in situ digestibility based on incubations in        digestion of the food may be initiated in the
bags (in sacco) in the digestive tract, e.g. after   mouth, where it may be disintegrated by chew-
incubation in the rumen or throughout the            ing. Although birds have no teeth, they may
intestine (mobile nylon bag) with collection at      use their beaks to reduce the size of food com-
the end of the ileum through a cannula, or in        ponents. During the process of mastication,
the faeces; (ii) in vitro digestibility based on     saliva is added. In the saliva of many animals
incubation with enzymes similar to those             an -amylase initiates the enzymatic degrada-
occurring in the digestive tract; (iii) chemical     tion of starch. In very young pigs, salivary
composition; and (iv) physical methods based         amylase is low; it increases slightly between 2
on near infrared, NIT, nuclear magnetic              and 3 weeks of age and then falls to very low
resonance or other methods, alone or in              levels. In young (suckling) animals, a lipase ini-
combination with chemical analyses.                  tiates the degradation of milk lipids. The saliva
     Availability is often used as a synonym for     provides a source of N (from urea and muco-
digestibility but also has a different meaning       proteins), P and K, which in ruminants are
(see Availability).                          (SB)    essential for the microorganisms in the rumen.
See also: Markers; Protein digestibility                 Some species have a forestomach: birds
                                                     have a crop which serves as a storage organ
Further reading                                      in which microbial fermentation may occur
D’Mello, J.P.F. (2000) Farm Animal Metabolism        together with a continued action of salivary
   and Nutrition. CAB International, Wallingford,    amylase on starch degradation; in ruminants
   UK, 438 pp.                                       the rumen, together with the reticulum and
                                                     omasum, are considered as forestomachs to
Digestible energy           That part of the         the abomasum, which corresponds to the true
gross energy of a food substance or complete         (gastric) stomach of non-ruminants.
ration which is not expelled as the gross                Protein digestion begins in the stomach,
energy of faeces. It is widely used to express       where pepsins cleave some of the peptide link-
146                                           Digestion




ages. Like many of the other enzymes involved        secreted from the pancreas into the duodenum
in protein digestion, pepsins are secreted in        in most non-ruminants, except the horse. In
the form of inactive precursors (proenzymes)         bovine species there is generally little pancre-
and activated in the gastrointestinal tract. The     atic amylase. Thus, the pre-ruminant calf can-
pepsin precursors are called pepsinogens and         not utilize starch, and adult cattle fed diets rich
are activated by gastric hydrochloric acid.          in grain may develop digestive disturbances
Pepsins are most active at pH 1.5 to 3 and           when large amounts of starch enter the small
hydrolyse the bonds between aromatic amino           intestine. Carnivores have little or no amylase
acids, such as phenylalanine or tyrosine, and a      activity. -Amylase does not hydrolyse the
second amino acid. A gelatinase that liquefies        chain branches of amylopectin or the terminal
gelatin is also found in the stomach. Rennin         bonds. Therefore, the products of amylase
(chymosin), a milk-clotting enzyme, is present       action in the intestinal lumen are disaccharides
at birth and disappears after weaning. Pepsin        such as maltose and isomaltose, trisaccharides
activity is very low (or absent) during the first 2   and limit dextrins with at least five and an aver-
weeks after birth but then increases rapidly,        age of eight glucose units. These products must
together with HCl production.                        be further hydrolysed to their monosaccharide
    In the small intestine, shortly after passing    constituents before they can be transported
the pylorus, the digesta are mixed with an           into the epithelial cells. The enzymes for per-
alkaline juice which neutralizes the acid            forming these last hydrolyses are attached to
digesta from the stomach and also contains a         the membranes of the microvilli of the brush
variety of digestive enzymes from the pan-           border and include maltase, isomaltase, glu-
creas: proteases, amylase, lipases and nucle-        coamylase and limit dextrinase. Other saccha-
ases for digesting proteins, starch, lipids and      rases are lactase, sucrase and trehalase.
nucleic acids. In some species the pancreatic        Lactase activity is high in mammals at birth and
duct is joined by the hepatic duct that trans-       remains high for the first 2–3 weeks of life,
ports bile from the liver. Bile salts are impor-     after which it declines rapidly. Birds do not
tant for lipid absorption.                           have lactase activity and ruminants do not have
    Polypeptides formed by digestion in the          sucrase activity. In pigs, sucrase and maltase
stomach are further degraded in the small            activities are low at birth and then rise with
intestine by the proteolytic enzymes of the          age. Enzyme changes in early-weaned pigs
pancreas and intestinal mucosa. The pH is            occur more rapidly than in sow-reared pigs, but
about 6.5. Trypsin, the chymotrypsins and            age has a greater effect than diet on the devel-
elastase act at interior peptide bonds in the        opment of intestinal brush-border enzymes.
peptide molecules and are called endopepti-              Lipids are hydrophobic and need to be
dases. The carboxypeptidases of the pancreas         emulsified (breakdown of fat globules into
and the aminopeptidases of the brush border          smaller globules) before they can be digested
are exopeptidases that hydrolyse the amino           by the hydrolytic enzymes lipase and phos-
acids at the carboxy- and amino- ends of the         pholipases. They are initially emulsified in the
polypeptides. Some amino acids are liberated         stomach as a result of stomach motility and
in the intestinal lumen, but others are liber-       are further emulsified in the small intestine by
ated at the epithelial surface by the                bile salts and lecithin secreted from the liver.
aminopeptidases and dipeptidases in the              The major component of lipids, triglycerides,
brush border of the mucosal cells. Some di-          are only partly digested before absorption.
and tripeptides are actively transported into        Fatty acids in position 1 and 3 are hydrolysed
the intestinal cells and hydrolysed by intracel-     and, after forming micelles (microemulsions),
lular peptidases, with the amino acids entering      become available for absorption, together
the bloodstream. Thus, the complete diges-           with the remaining 2-monoglyceride, glycerol,
tion of protein to amino acids occurs at three       cholesterol and other lipids.
locations: the intestinal lumen, the brush bor-          Nucleic acids, DNA and RNA, are digested
der, and the cytoplasm of the mucosal cells.         by deoxyribonuclease and ribonuclease
    Starch consists of amylose and amylopectin.      secreted from the pancreas and are further
Large quantities of pancreatic amylase are           degraded to pentoses and purine and pyrimi-
                                         Digestive disorders                                      147




dine bases by nuclease and related enzymes          as loss of appetite and production. Also in
attached to the brush border. Absorption of         dairy cows, the inadequate supply of acetate
digested products is completed in the ileum.        and butyrate, which are the precursors of milk
    In the large intestine, microbial enzymes       fat synthesized de novo in the mammary
contribute to the digestion in all animal           gland, leads to a low milk fat syndrome, which
species and are in many cases of significant         can be rectified by reducing the quantity of
importance. The major microbial end-prod-           rapidly digestible substrate fed at any one time.
ucts of fermentation are short-chain fatty          The feeding must be changed either to fibre-
acids (SCFAs) and ammonia, which are                based energy sources, such as fodder beet, or
absorbed. SCFAs are an important energy             to a starch-based energy source in small quan-
source for the epithelial tissue but may also       tities at regular intervals of the day. Some ben-
contribute considerably to the general energy       efit can also be obtained by feeding the cereals
supply of herbivorous animals, e.g. up to 75%       in a mixture with forages.
in the horse. In ruminants, microbial digestion          The fermentation of food particles pro-
plays a particular role because the major part      duces gases, principally carbon dioxide and
of digestion takes place in the rumen.     (SB)     methane, which are liberated via the mouth by
See also: Digestibility; Gastrointestinal tract;    eructation. The rapid digestion of starch can
Intestinal absorption                               lead to the production of excessive gas which,
                                                    with diminished contractions of the reticuloru-
Digestive disorders             The function of     men, result in the animal becoming bloated.
the digestive system is to break down food par-     This ruminal tympany can be observed on the
ticles, physically and chemically, into a form      left-hand side of the animal, when viewed from
that is suitable for absorption into the blood      behind. Some legumes, such as lucerne or
system and subsequent utilization for metabolic     clovers, produce a stable foam in the rumen,
processes. There are many digestive disorders       through which the gases cannot be liberated.
in modern animal farming systems, principally       Others, such as bird’s-foot trefoil, contain tan-
because the nature of the food supply is differ-    nins that effectively bind the proteins to reduce
ent to that available to their ancestral progeni-   the rate of digestion and make them ‘bloat-
tors. The digestive system of farm animals          safe’. The feeding of fibrous forages will be
evolved to digest foods that were often very        beneficial in cases of bloat, as it reduces the
different to those that can be easily provided in   rate of digestion. Ruminants will go to consid-
modern farming systems. In addition, the            erable lengths to consume adequate fibre to
genetic modification of farm animals to              stimulate rumination. Ruminal atony predis-
increase productivity requires that the nutrient    poses ruminants to tympany, but the con-
density of the diet be increased above that         sumption of pseudofibrous material can cause
which the wild ancestors of farm animals            digestive disorders, such as calves that lick
would have consumed. This is important for          each other’s coats and develop hairballs, or
the energy and protein supply for ruminants,        chickens that get an impacted crop. Cattle also
which evolved to utilize coarse grasses.            develop abscesses when they consume plants
    In the case of lactating cows, a diet of        with awns that irritate the gastrointestinal tract.
coarse grasses and browse material has been              Salivation is an essential process to add
necessarily replaced by lush grass, with a high     moisture to the food, which together with
water-soluble carbohydrate content, and cereal      mastication prepares the food for passage
grains containing starch that is rapidly digested   into the gastrointestinal tract. It also adds
in their rumen. Excessive processing of cereals     digestive enzymes, principally amylases and
exposes the starch to rapid fermentation. After     buffer salts. The salts are particularly impor-
a meal, the rapid production of fatty acids as a    tant to increase rumen pH in cattle and
result of bacterial growth on the readily avail-    sheep, which allows digestion of fibre to pro-
able substrate can lead to a reduction in rumen     ceed. Excessively wet feeds, such as lush
pH below the normal 6–7 (clinical acidosis),        grass, which may have a dry matter concen-
which reduces the potential growth of cellu-        tration of only 10–12%, may promote aci-
lolytic bacteria in particular and is manifested    dotic conditions in the rumen. Saliva also
148                                   Digestive enzyme inhibitors




contains mucins, which are believed to coun-         rather than suckling with the head held hori-
teract ruminal tympany – a problem that is           zontally, milk may enter the rumen and cause
worst following consumption of herbage of            diarrhoea, or ‘calf scours’. Specific nutrients
low dry matter content.                              consumed in excessive quantities, such as
    Vomiting is a digestive disorder that func-      lipids, can upset the bacterial digestion in the
tions to reduce the digestion of potentially         rumen. Similarly, the consumption of some
harmful material. It can also be triggered by        minerals (e.g. potassium) in excess can reduce
motion sickness in animals in lorries or suffer-     the absorption of others (e.g. magnesium)
ing from intense fear or an infection. A stereo-     through competitive inhibition.
typed vomiting disorder can develop in                   Digestive disorders are a serious problem
primates in stressful conditions. Diarrhoea,         in farm animals and can lead to low growth
too, functions to reduce the time for which          rates and low milk production. This is particu-
potentially toxic elements are present in the        larly the case in high-producing ruminants,
gastrointestinal tract, but can also be triggered    where there is a significant difference in the
by gastrointestinal infection, typically by para-    diet fed from that available to their ancestral
sites or bacteria. Parasites may damage the          progenitors. Further research is required to
absorptive surface of the gastrointestine, espe-     devise feeding regimes for farm animals that
cially the intestinal villi, thus reducing mineral   cater for their level of productivity.   (CJCP)
uptake. Diarrhoea is commonly caused by an
excessive intake of rapidly digestible nutrients.    Digestive enzyme inhibitors                  Sub-
One of the most common instances occurs              stances that inhibit the activity of one or more
when ruminants graze lush pasture in spring.         digestive enzymes. Nutritionally, the most
In this case the absorption of some critical         important of these are the protease
minerals, such as magnesium, can be reduced          inhibitors, which are widespread in the
by the short turnover of feed in the rumen.          seeds of many plants, especially legumes.
    Stress, which is common in many inten-           They are proteins which form stable inactive
sively managed farm animals, will exacerbate         complexes with digestive enzymes, especially
several digestive disorders, including diarrhoea     trypsin and chymotrypsin, and are called
and vomiting. The frequency of defecation, as        trypsin inhibitors. The activity of these
well as the dry matter content of the faeces,        inhibitors, both in their relative and their total
will indicate stress. The extent to which dairy      amounts, varies greatly amongst species of
cows are stressed by contact with their              legume, and between varieties of the same
herdsperson can be estimated by whether they         species. They are inactivated by appropriate
defecate when they are milked by that person.        heat treatment and such treatment often
Gastric ulcers develop in pigs in intensive          forms part of the processing of the seeds for
housing, due to excessive acid production.           inclusion in feeds, especially for non-rumi-
    Low intakes of food can reduce digestibility,    nants. Diets containing large amounts of
at least in the short term, due to insufficient       trypsin inhibitors cause hypersecretion and
nutrients to support an adequate concentration       enlargement of the pancreas, reduce the
of microorganisms in the rumen. In the long          digestion of dietary proteins and increase the
term, digestibility usually increases, due to        loss from the gut of endogenous nitrogen.
increased chewing of the food and reduced               Amylase inhibitors also occur in certain
losses of nitrogen and other nutrients in fae-       legume seeds but do not appear to be of great
ces. Excessive intakes of food, apart from the       nutritional importance.
problems of bloat referred to above, can cause          The actions of digestive enzymes on plant
difficulties if the food particles enter the wrong    proteins can also be impaired by the presence
compartments. In milk-fed calves the milk nor-       in the diet of other antinutritional factors,
mally bypasses the rumen to be digested in the       such as non-starch polysaccharides and phe-
abomasum; but if the reticular groove does not       nolic compounds, and by the physical barrier
function adequately, such as is common in            of indigestible plant cell walls which impede
calves drinking large quantities of milk from        access of digestive enzymes to the substrates
buckets with the head facing downwards,              within the cells.                            MFF
                                         Direct calorimetry                                    149




Digestive system           The complex of           oxyacetic acid (2,4,5-T) and also as a com-
organs that participate in the digestion of         ponent of the defoliant agent orange and in
food. The system comprises the entire gas-          wood preservatives (pentachlorophenol).
trointestinal tract and its accessory organs.       Dioxins can be formed by combustion at low
These include the salivary glands, the pan-         temperature in the presence of carbon and
creas and the liver, which secrete enzymes,         chlorine. They persist in the environment
bile acids and other substances into the gut        and accumulate in the fatty tissue of living
lumen, and the portal circulation, which car-       organisms.
ries away the products of digestion to the rest                          10
of the body.                             (MFF)        Cl          1                9
                                                                                             Cl
                                                                          O
                                                              2                         8
Dihomo- -linolenic acid            All cis 8,11,
14 eicosatrienoic acid, molecular structure
CH 3·(CH 2) 4·(CH=CHCH 2) 3·(CH 2) 5·COOH,                    3                         7
                                                      Cl                  O                  Cl
                                                                  4                6
molecular weight 306.5, shorthand designa-                                5
tion 20:3 n-6. A fatty acid of the n-6 family                           TCDD

synthesized from linoleic acid by successive                                                 (JEM)
∆6 desaturation and chain elongation; it is
also called homo- -linolenic acid.         (DLP)    Dipeptidase          A peptidase that specifi-
                                                    cally hydrolyses dipeptides. Dipeptidases are
Dihydrofolate           C19H23N7O6, the first        located together with tripeptidases and
intermediate in the conversion of folic acid (a     aminopeptidases in the brush border of the
B vitamin) to its tetrahydrofolate form by the      epithelial cells of the small intestine, mainly
enzyme folate reductase. After modification          the jejunum.                              (SB)
by addition of -glutamyl residues, tetrahydro-      See also: Digestion
folate is the coenzyme form of the vitamin.
Tetrahydrofolate and the folate system are          Dipeptide         R·C=O·NH·C·R, a molecule
critical to the synthesis of the purines used in    formed of two amino acids linked by a pep-
DNA synthesis.                             (NJB)    tide bond. In the digestion of protein, some
See also: Folic acid                                dipeptides are formed and absorbed into the
                                                    enterocyte prior to being hydrolysed to single
Dilution rate        The rate at which fluid or      amino acids. In special cases dipeptides are
solids in the freely mixing, constant-volume        formed from cellular amino acids. These
content of a compartment of the gut (e.g.           include carnosine ( -alanylhistidine), anserine
reticulorumen) is replaced. Units are % h 1,        ( -alanyl-1-methylhistidine) and balenine ( -
fraction h 1, etc.                    (RNBK)        alanyl-3-methylhistidine).               (NJB)

Dimethylsulphoxide (DMSO)                           Direct calorimetry           Direct calorime-
(CH3)2·SO, a hygroscopic liquid that is mis-        ters not only measure the total heat given off
cible with water. It readily penetrates tissues     by animals, but also partition it into its two
and is used as a solvent for delivery of drugs to   components, evaporative and non-evapora-
the bloodstream by topical application. (NJB)       tive. Non-evaporative or sensible heat is heat
                                                    given off from an animal by radiation to sur-
Dioxin          A family of more than 70            rounding surfaces, by convection to the sur-
chemical compounds, known as polychlori-            rounding air and by conduction to any objects
nated dibenzo-para-dioxins, that have an            with which the animal is in contact. Evapora-
identical carbon–oxygen ‘skeleton’ and con-         tive heat loss occurs because the conversion
tain one to eight chlorine atoms. The most          of liquid water into vapour requires heat
widely studied is 2,3,7,8-tetrachlorodibenzo-       energy. The latent heat of vaporization is the
p-dioxin (TCDD), a known carcinogen, ter-           heat required to vaporize unit mass of water;
atogen and mutagen. Dioxins were found as           it varies from 2490 to 2390 J g 1 (595–572
contaminants in the herbicide trichlorophen-        cal g 1) within the temperature range
150                                     Direct calorimetry




0–40°C. When water is vaporized in the res-        ters required a team of three or four scientists
piratory passages during normal respiration        for their operation. The precision was truly
and panting, or at the skin surface during         remarkable and demonstrated (over periods of
perspiration, the latent heat of vaporization is   days) agreement between direct and indirect
given up by the animal. This heat loss by the      calorimetry to within 1%. At the time this was
animal is transferred to the air in the form of    hailed as proof that the first law of thermo-
increased humidity; the enthalpy of the air        dynamics applied to living systems as well as
(which is a measure of its energy content and      to mechanical ones. Nowadays that would be
depends on temperature, humidity and pres-         accepted as axiomatic and the agreement
sure) is increased.                                between direct and indirect calorimetry would
    Direct calorimeters are classified into four    be regarded as proof of the accuracy of the
types (isothermal, heat-sink, convection and       measuring systems.
differential) according to how sensible heat is        In recent years the technique of heat-sink
measured. In isothermal calorimeters the           calorimetry has been revived and refined but
sensible heat is measured as it passes             mainly applied to studies on humans. For ani-
through the walls, floor and ceiling of the         mals, recent use of heat-sink, convection and
animal chamber; these surfaces have heat-          differential calorimeters has been confined to
sensitive linings which generate voltages pro-     studies on laboratory animals and poultry.
portional to the heat passing through. In          The most favoured method for farm animals
heat-sink calorimeters the chamber surfaces        has become the isothermal one, the modern
are thermally insulated and the sensible heat      form of which is the gradient-layer calorime-
from the animal is taken up by a heat              ter.
exchanger; the heat is measured as the prod-           In the gradient-layer calorimeter the sensi-
uct of the temperature rise of the coolant         ble heat from the animal generates a small
and its rate of flow. Convection calorimeters       temperature gradient across a thin uniform
also have insulated surfaces and ideally all       layer, usually of plastic material, as it passes
sensible heat from the animal is taken up by       into a water-cooled jacket surrounding the
the ventilating air, whose temperature             chamber. The mean temperature gradient (i.e.
increase multiplied by flow rate provides the       temperature difference) across the layer is
measure of the heat. This method tends to          measured by multiple and/or widespread sen-
be slow in response because after a change         sors on either side (thermocouples, thermis-
in the level of heat output there is a delay       tors or resistance thermometers) and
while the chamber itself, especially its insu-     generates a voltage output that is proportional
lated walls, adjusts to the new level. To over-    to the integrated heat flow through all sur-
come the delay, differential calorimeters          faces, i.e. the sensible heat output from the
employ two similar chambers, one contain-          animal. Evaporated water is reconverted into
ing the animal and the other an electrical         liquid by passing exhaust air between cooled
heat source; the power provided to the             plates that return its humidity to the original
heater is controlled to produce the same           level it had before entering the chamber; the
increase in air temperature as that in the ani-    heat of re-condensing it, which is equal to the
mal chamber and it thus represents the sen-        evaporative heat loss of the animal, is again
sible heat output of the animal. In heat-sink,     measured by gradient layers covering the
convection and differential calorimeters,          plate surfaces. Because the gradient layers are
evaporative heat is measured as the increase       thin and the temperature differential across
in humidity of the ventilating air, usually        them no more than a fraction of a degree, the
sensed by dewpoint hygrometers or wet-and-         time response to changes in heat output is
dry-bulb thermometers.                             only a few minutes. The principal limitation to
    The earliest calorimeters for farm animals     the speed of response of a gradient-layer
were of the heat-sink type and much pioneer-       calorimeter is not the calorimeter itself, but
ing work was done in them 100 years ago.           the relatively slow response to heat changes
None of today’s sophisticated electronic con-      of any cage or bars fixed inside it to restrain
trol systems were available and most calorime-     the animal.
                                         Distillers’ residues                                       151




    Ventilation of a direct calorimeter has to be    Distillers’ residues           Materials that arise
sufficient to ensure control of air temperature       from (or remain after) the distilling process.
inside the chamber and to avoid condensation         Distilling, which is basically the conversion of
of evaporated water inside it. Pre-conditioning      cereal starch into ethyl alcohol, takes two
all the ventilating air and then exhausting it to    forms. Malt distilling uses only malted barley
the environment would be wasteful of power           as a substrate and grain distilling traditionally
and so most of the air is usually recirculated       used maize and malt but recently, in Scotland
round a closed circuit, with only a small pro-       at least, increasing proportions of wheat have
portion being voided to the atmosphere and           been used. Residues suitable for use as animal
replaced with fresh air. The oxygen and car-         feeding stuffs arise at all stages of the distilling
bon      dioxide    concentration     differences    process, from the initial screening of malt or
between fresh and exhaust air can be made of         cereal grains to the liquids remaining after the
the order of 1%, and conveniently measurable         alcohol has been distilled off.
so that indirect and direct calorimetry may be            As in brewing, ground malt, other cereals
performed at the same time.              (JAMcL)     or both are mixed with hot water to form a
See also: Calorimetry; Heat balance; Indirect        ‘mash’ in which the enzymatic conversion of
calorimetry                                          starch to disaccharide sugar takes place or is
                                                     completed. The liquid phase (wort) containing
                                                     the soluble components, primarily sugars and
Further reading                                      some protein, may be separated prior to fer-
McLean, J.A. and Tobin, G. (1987) Animal and         mentation (usual in malt distilleries) or yeast
  Human Calorimetry. Cambridge University            may be added to the whole mash. When fer-
  Press, Cambridge, UK, 338 pp.                      mentation is complete the alcohol is distilled
                                                     off. The mix of liquid and solids remaining
Disaccharidases          Enzymes that hydro-         after fermentation of and distillation from the
lyse molecules made up of two sugars. In ani-        whole mash is known as thin stillage. Solids
mals they are found in the brush border of the       and liquid are separated when distillation is
enterocytes of the small intestine. The              complete.
enzyme that hydrolyses the two-sugar unit                 The solid residues, which are primarily the
maltose from starch digestion is maltase; that       fibrous portion of the cereal grain, whether
hydrolysing lactose is lactase; and that             extracted before or after fermentation and dis-
hydrolysing sucrose is sucrase.         (NJB)        tillation, are known in Scotland as draff whilst
                                                     the liquids are known as ‘pot ale’ (malt distill-
Disaccharides          Sugars made up of two         ing) and ‘spent wash’ (grain distilling). These
monosaccharide molecules. They can be                liquids contain disrupted yeast cells as well as
reducing sugars, which have a potential car-         residues of substances solubilized from malt
bonyl carbon, or non-reducing sugars, which          and cereal grains and are usually concentrated
do not. Disaccharides important in animal            by evaporation to produce pot ale and spent
nutrition include the reducing sugars maltose        wash syrups. Traditionally much of the syrup
(made up of two glucose units) and lactose           was dried to produce a fine, mildly hygro-
(made up of glucose and galactose) and the           scopic meal known as dried distillers’ solubles.
non-reducing sugar sucrose (made up of glu-          More usually now, the syrups are mixed back
cose and fructose). Another non-reducing di-         with the solid residues. This mix may be made
saccharide of note is trehalose; other reducing      available as ‘super draff’ or dried and pelleted
disaccharides include cellobiose, gentiobiose,       to produce distillers’ dark grains (distillers’
melibiose and turanose.                   (NJB)      grains with solubles). Occasionally, though
                                                     rarely now, the solid residues may be dried
Disorders, nutritional: see Nutritional dis-         without the addition of a syrup, when they are
order                                                referred to as distillers’ light grains. Syrups
                                                     may also be used directly or blended with
Dispensable amino acids: see Non-essen-              other materials such as molasses to produce
tial amino acids                                     liquid feeding stuffs.
152                                             Diurnal variation




Composition of distillers’ residues.

                                Dry matter   Crude protein Ether extract Crude fibre  Ash         MER
                                 (g kg 1)    (g kg 1 DM) (g kg 1 DM) (g kg 1 DM) (g kg 1 DM) (MJ kg 1 DM)

Pot ale syrup                      450           360           30         <5          100         14.5
Spent wash syrup – maize           360           300           70        < 10          80         16.0
Spent wash syrup – wheat           300           350           20          25          60         15.0
Malt distillers’ dark grains       890           260           60         140          55         12.0
Maize distillers’ dark grains      890           300          100          90          50         14.0
Wheat distillers’ dark grains      890           300           60          75          50         12.5

MER, metabolizable energy for ruminants.

   When referring to distillers’ residues it              Docosahexaenoic acid (DHA)                    An
should always be made clear from which                    unsaturated 22-carbon fatty acid with six dou-
cereal they were derived, e.g. malt screenings,           ble bonds (22:6, 4,7,10,13,16,19), a member of
maize distillers’ light grains, pot ale syrup or          the n-3 family. In metabolism it can be syn-
wheat distillers’ dark grains.                            thesized from -linolenic acid by sequential
   Distillers’ residues are used in the diets of          desaturation and two-carbon elongation reac-
pigs, poultry and ruminants but their fibrous-             tions. DHA can be obtained directly from fish
ness and the nature of the protein make them              oils and is in high concentrations in the brain,
most suited to feeding ruminants. Typical crude           retina and testis. In the retina it is a compo-
analyses of three syrups and three types of               nent of the membrane phospholipid fraction
dark grains are as shown in the table.     (CRL)          and is thought to lead to the enhanced fluidity
                                                          needed for the visual process. It is particularly
                                                          concentrated in the sn-2 position (i.e. 2-car-
Further reading                                           bon of glycerol) of phosphatidylethanolamine.
Crawshaw, R. (2002) Co-product Feeds – Animal
                                                                                                     (NJB)
   Feeds from the Food and Drinks Industry.
   Nottingham University Press, Nottingham, UK,
   307 pp.                                                Docosapentaenoic acid           A 22-carbon
Gizzi, G. and Givens, D.I. (2001) Distillers’ dark        unsaturated fatty acid with five double bonds
   grains in ruminant nutrition. Nutrition                (22:5, 7,10,13,16,19), a member of the n-3
   Abstracts and Reviews Series B: Livestock              family.                                (NJB)
   Feeds and Feeding 71(10), 1R–19R.
                                                          Domestic fowl             The genus Gallus,
Diurnal variation           A term applied to             belonging to the order Galliformes, suborder
numerous circadian rhythms and used to                    Phasiani, family Phasianidae, subfamily
describe predictable daily variation in the               Phasianinae. The four species in the genus,
intensity of a physiological function. This vari-         which have the common name junglefowl,
ation is thought to occur in all living organ-            have their origin in South-east Asia: the red
isms. The 24-hour light/dark cycle is involved            junglefowl, Gallus gallus, the grey junglefowl,
in setting the daily rhythms of neural activity,          Gallus sonneratii, the Ceylon junglefowl,
body temperature cycle, sleep, feeding and                Gallus lafayetii, and the green junglefowl,
fasting, physical activity cycle, blood concen-           Gallus varius.
trations of hormones and metabolites, etc.                   The most widespread is the red junglefowl,
                                           (NJB)          within which there are five subspecies: G. g.
See also: Circadian rhythm                                murghi, G. g. spadiceus, G. g. jabouillei, G.
                                                          g. gallus and G. g. bankiva. As a species the
Docosaenoic acids           Unsaturated fatty             red junglefowl is not threatened. It is most
acids with 22 carbons. In the n-3 (or 3) fam-             numerous in Thailand, where G. g. spadicus
ily the first double bond occurs on carbon 19              and G. g. gallus have part of their habitat
(i.e. 22–3) whereas in the n-6 ( 6) family the            range. Recent DNA analyses of these sub-
first double bond is on carbon 16.       (NJB)             species have indicated that G. gallus was the
                                    Double isotope techniques                                 153




originating species of the domestic fowl.         away from whole carcasses to portions or
Domestication, from about 6000 BC, exploited      stripped meat, the high-yielding feed-efficient
the bird for sport and food. Breed develop-       breeds have succeeded.
ment across Asia and Europe was limited until         A modern broiler breeder produces 140
the 19th century, when the larger Chinese         chicks to 65 weeks of age with a feed intake
breeds arrived in Europe and the USA. The         per chick of about 350 g. The broilers can be
majority of breeds are for show purposes.         slaughtered over a wide weight range, typi-
Those developed for commercial purposes           cally from 32 days to 50 days of age. This is
have a mature body size ranging from 1.5 to       to provide everything from whole small
6.5 kg. Breeds at the lower end of the range      chicken carcasses to heavy males for meat
are used for egg production and those at the      stripping. Males and females are normally
upper end are used for meat.                      grown separately to allow maximum efficiency
    Both laying hens and meat chickens are        of production. The breeds differ in their
derived from the same species. The modern         growth pattern and yield characteristics but
hybrid layer can be divided into two main         are very similar in weight for age, FCR and
groups: the light breeds and the heavy breeds.    mortality.
The former are mainly derived from White              Birds are normally kept in controlled envi-
Leghorns, laying white eggs, while the heavy,     ronment sheds on the floor with ad libitum
less feed-efficient brown layers come mainly       access to feed and water. Broiler performance
from Rhode Island Red stock. Worldwide            is continuously improving, due to genetic
there are currently some ten major breeds,        selection, with birds typically reaching target
with most breed companies offering a choice       weight 1 day earlier each year. This gives a
of at least three strains: brown and white egg    corresponding improvement in feed efficiency
layers and a more traditional strain for exten-   of several points per annum.
sive/alternative systems.                             Metabolism does not differ greatly between
    Modern breeds are capable of producing        breeds, although the pattern of early growth
20 kg of egg mass output to 76 weeks, with a      is breed specific. The nutrient requirements
feed conversion ratio (FCR) of 2–2.2:1. This      are set out in manuals provided by the breed
is typically obtained by producing 320+ eggs,     companies. In practice, integrated companies
average weight 63 g, on a daily consumption       with more than one breed tend to produce
of around 112 g of feed. Breeds may differ in     only one set of diets.              (WKS, KF)
average egg weight and have different shell
quality characteristics. Some are more feed       Dopamine           Dopamine (3-hydroxytyra-
efficient than others but no one strain is per-    mine or 3,4 dihydroxyphenethylamine) is one
fect, since different markets require different   of the catecholamines and is a neurotransmit-
products. Alternative systems require greater     ter. It is produced by a hydroxylation and
egg size, shell egg markets emphasize shell       decarboxylation of the aromatic amino acid L-
quality, while for the liquid-egg market feed     tyrosine in the substantia nigra in the brain. In
efficiency is most important.                      Parkinson’s disease, production of dopamine
    The world market for meat birds, be it        is insufficient to maintain dopaminergic neu-
chicken or turkey, is now dominated by five        ron function.                              (NJB)
major companies, along with some smaller          See also: Neurotransmitter
organizations producing speciality products.
Several companies offer a choice of products,     Double isotope techniques                 Also
depending on market requirements, while oth-      called double labelling, used to trace the fate
ers have only a simple compromise bird.           of nutrients or metabolites in the body. For
Heavy meat breeds now dominate the world          example, an amino acid labelled with both
stage. Historically there were light breeds       15N and 13C can provide information on the

where the breeder bird produced large num-        metabolic fate of both the nitrogen and the
bers of chicks, which grew less efficiently,       carbon in the amino acid molecule. Doubly
with lower meat yields. With the huge world-      labelled water is used to estimate CO2
wide demand for poultry meat and the move         production.                              (MFF)
154                                    Doubly labelled water




Doubly labelled water           Water contain-     ing. The high-temperature drying process not
ing isotopes of both hydrogen and oxygen,          only removes the water content of the plant
usually deuterium (2H) and 18O. Its usual use is   but at the same time reduces the degradability
for the estimation of carbon dioxide produc-       of the proteins, protecting approximately 50%
tion. The principle of this method is that         of the protein from degradation in the rumen,
when doubly labelled water (2H18O2 ) is intro-     making it available for digestion in the small
duced into the body, both elements are lost as     intestine. Dried lucerne contains only 10% of
water but oxygen is lost additionally as CO2.      crude protein as non-protein nitrogen (NPN),
By measuring the rate of decline in the con-       against 55% of crude protein as NPN for
centrations of both isotopes in the body water     lucerne when it is ensiled.
pool, this additional loss of oxygen can be
                                                   Typical analysis of dried lucerne.
estimated and, from it, the rate of CO2 pro-
duction. The method can integrate CO2 pro-         Dry matter (DM)                      88%
duction over a period of days or weeks and is      Protein                              18–20% of DM
thus particularly suitable for measurements in     Metabolizable energy                 10.0 MJ kg 1 DM
free-living animals.                      (MFF)    Neutral detergent fibre               42–45% of DM
                                                   Acid detergent fibre                  32–35% of DM
Draught animals: see Working animals               Oil                                  3% of DM
                                                   Ash                                  11% of DM
                                                    -Carotene                           80 mg kg 1
Dressing percentage             Carcass weight     Vitamin E                            120 mg kg 1
as a proportion of the liveweight at slaughter.    Calcium                              3% of DM
Carcass weight may include the head, feet,         Phosphorus                           0.3% of DM
tail, etc., but sometimes does not.      (MFF)
                                                                                                     (RJ)
Dried grass          The procedure for drying      See also: Lucerne
grass differs from hay and barn-dried haymak-
ing because it involves the rapid evaporation      Dried milk      Milk (whole or skimmed)
of plant juices by hot air with minimum losses     dried to a powder by spray drying or roller
of nutrients. Although this process is the most    drying.                             (PCG)
effective in retaining the nutritional value of
the fresh grass, it is also extremely costly.      Dried skimmed milk              Skimmed milk
Both capital outlay and running costs are          dried to a powder, usually by spray drying.
high. The nutritive quality of dried grass is                                               (PCG)
high and the process is commanding greater
attention due to the need to rely less on          Dried whey             Whey dried to a powder by
imported concentrates. Dried grass is nor-         spray drying.                             (PCG)
mally marketed with protein contents of
between 14 to 20% dry matter (DM), metabo-         Drinker         A device for providing fresh
lizable energy > 10.8 MJ kg 1 DM, and a DM         drinking water to domestic livestock. This can
content > 90%. The final dried grass material       range in size from a bath tub or trough with a
may be sold finely chopped or in the form of        ball-cock mechanism for flow control, as used
pellets. Dried grass is a very palatable feed      for cattle or sheep out at grass, to a tiny nip-
and the forage substitution rate (kg reduction     ple, as used by caged laying hens. A drinker
in forage DM intake per kg DM of supple-           can be as simple as a manually filled basin for
ment fed) is similar to that of average grazed     extensive ducks, or as complex as a time-reg-
grass and better than good quality silage of       ulated bell drinker that allows broiler breeders
maize or grass.                             (RJ)   to consume only a set volume of water each
                                                   day. Sheep and cattle drinkers tend to be
Dried lucerne          Dried lucerne (alfalfa,     large vessels with simple mechanisms to stop
Medicago sativa) is usually chopped and then       wastage. For pigs, on the other hand, drinkers
dried at a very high temperature (800°C)           often incorporate a pressure switch activated
before further processing by pressing or pellet-   by the snout to control the flow of water. For
                                              Drought                                               155




intensive poultry also it is important to avoid     Drinking water: see Water
wastage. Spillage from nipple drinker systems
is often reduced by the use of a cup hung           Drought           Drought occurs where the
underneath. In most production systems              supply of water falls below the critical demand
smaller and more refined drinkers are used           in an area over a prolonged period. The
with infant livestock, such as mini jars for        demand is usually a function of human activi-
poultry, small nipples for pigs and plastic teats   ties and droughts can therefore be considered
for calves and lambs.                        (KF)   man made. In contrast, an area with low rain-
                                                    fall is described as arid, but the ecology of the
Drinking behaviour            There are several     flora and fauna are adapted to the periodic
methods of drinking used by domesticated            absence of water.
animals. While cattle, horses and sheep form            Droughts lead to feed shortages and loss of
their lips into a tube and suck, pigs gulp water    production principally in grazing stock, and
and poultry depend on gravity for transferring      usually have their origin in the rainfall and
water to the alimentary tract. When drinking        plant production of the preceding season. The
from bell or cup drinkers (usually situated         declaration of drought will be made after a
below head height), domestic fowls make a           short dry period in the case of high output
series of angled dips of the open beak into the     stock, such as dairy cows, where as little as 1
water and raise the head between each dip to        month without rain may substantially reduce
let the water pass from the mouth into the          production, and after a long period in the
oesophagus. When drinking from nipple               case of stock of low productivity, such as
drinkers (usually above head height), they          Merino sheep, where a drought may extend
extract water with varying efficiency and let it     for several years before a serious loss of pro-
trickle down while keeping the head raised.         ductivity is experienced. Thus intensification
Typically, fowls spend more time drinking           of pasture and animal production will increase
from nipples (about 6% of time) than from           the risk of drought and increase the variation
bell or cup drinkers (about 3%), because water      in profitability of the enterprise. Drought will
flow rate is limited with nipple drinkers.           also influence the diseases affecting grazing
    Feed intake is the main determinant of          stock, with plant poisoning being common as
water requirement when ambient temperature          animals search for fodder, as well as osteoma-
is within the thermoneutral zone, and most          lacia and botulism. The congregation of live-
drinking occurs in close association with spon-     stock around small waterholes can facilitate
taneous meals. Typically, animals consume           the spread of infectious diseases such as
about 1.6–2.2 times as much water as food           tuberculosis and brucellosis.
per day, by weight. However, some drink                 The impact of droughts can be buffered by
more than would be expected from their daily        feeding supplements to livestock, by sale of
food intake, possibly as a consequence of           stock or their agistment or, in highly intensive
environmental stress, and such excessive            systems, by the use of artificial irrigation for live-
drinking (polydipsia) can be very marked in         stock crops. Usually grain or hay is used as a
animals subjected to chronic food restriction.      supplement. It is important that a drought man-
When ambient temperature is above the               agement strategy is planned in years between
thermoneutral zone, animals need to drink           droughts. The strategy should include estimates
more water to replace evaporative water loss        of drought frequency, the cost of supplementa-
due to sweating and panting. Physiological          tion, the financial gain from maintaining live-
control of water intake is based mainly on          stock growth and the impact on stock welfare.
changes in cellular hydration, through              Drought frequency can now be estimated in
osmoreceptors, but also on changes in plasma        many regions, since rainfall records have been
volume, through the rennin–angiotensin sys-         kept for at least 100 years. For example, it can
tem. Water consumption and the ratio of             be determined that a major drought will occur in
water to food intake are increased by high          central east Australia every 7 years, whereas in
dietary mineral and protein concentrations.         the south-east of that country it will only occur
                                     (JSav, JMF)    once every 11 years.                         (CJCP)
156                                         Dry matter




Dry matter          One of the terms used to       Table 1. Recommended moisture contents (%) of
describe the proximate composition of feed-        selected grains for storage.
stuffs. Most feedstuffs have water as part of
                                                                  Short term                Long term
their weight. In most cases dry matter is deter-
                                                             (less than 6 months)      (more than 6 months)
mined by the weight loss of samples dried in
an oven at temperatures above 100°C for            Barley              14                        12
12–24 h. Weight loss is equated to water and       Maize               15.5                      13
dry matter is calculated accordingly.     (NJB)    Oats                14                        12
                                                   Rye                 13                        12
Dry season          A time when no rain is         Wheat               14                        13
expected. In the tropics either one or two dry
seasons are normal. The long dry season is
usually relatively cool and can last many             Grain can be stored at a higher moisture
months. Plant growth ceases; termite damage        content without significant fungus develop-
and senescence reduce standing biomass.            ment when stored at colder temperatures.
Livestock depend on crop residues. In              Table 2 shows the relationship between mois-
extreme years, stock losses are common.            ture and temperature and its effect on allow-
                                          (TS)     able storage time for cereal grains.
See also: Wet season
                                                   Table 2. Guidance on storage time (days) for cereal grains.
Drying feed crops          The purpose of dry-
                                                                                Temperature (°C)
ing crops for animal feed is to allow safe stor-   Moisture
age with minimal losses and contamination.         content (%)     1        4     10      16       21     27

Grain                                              14             *        *       *       *       200   140
                                                   18             *       200     90      50        30    15
Some advantages of drying grain are that it: (i)
                                                   22            190       60     30      15         8     3
increases quality of harvested grain by reduc-
                                                   26             90       35     12       8         5     2
ing crop exposure to weather; (ii) reduces har-    30             60       25      5       5         3     1
vesting losses, including head shattering and
cracked kernels; (iii) reduces dependency on       * Storage time may exceed 300 days.
weather conditions for harvest; (iv) allows use
of straight combining for small grains; (v)
                                                       Airflow rate, air temperature and atmos-
reduces size and/or number of combines and
                                                   pheric relative humidity will influence drying
other harvest-related equipment and labour
                                                   speed. In general, higher airflow rates, higher
required due to extending harvest time; and
                                                   air temperatures and lower relative humidities
(vi) allows more time for postharvest field
                                                   increase drying speed. Raising the tempera-
work. Some disadvantages are: (i) the original
                                                   ture of the drying air increases the moisture-
investment for drying equipment and annual
cost of ownership; (ii) the operating costs for    carrying capacity of the air and decreases the
fuel, electricity and labour; and (iii) possible   relative humidity. As a general rule of thumb,
need for further investment in equipment for       increasing the air temperature by 7°C doubles
the extra grain handling that is required.         the moisture-holding capacity of air and cuts
    The length of time for which grain can be      the relative humidity in half.
stored without significant deterioration is             The drying rate depends on the difference
determined by the temperature and the mois-        in moisture content between the drying air
ture content at which it is stored. Table 1        and the grain kernel. The rate of moisture
shows the maximum recommended moisture             movement from high-moisture grain to air
contents for storage with duration for some        with low relative humidity is rapid, but the
typical feed grains. Short-term storage gener-     moisture movement from wet grain to moist
ally refers to storage under winter conditions     air may be very small. At high relative
while long-term storage includes the effect of     humidities, dry grain may pick up moisture
summer conditions.                                 from the air.
                                         Drying feed crops                                    157




    There are a number of different grain dri-         Natural dry matter losses in wilted crops
ers available commercially, including natural      are normally small, provided that the wilting
air, low temperature and high temperature, or      period is up to 2 days. If the pre-wilting
batch and continuous flow. Driers can also be       period is extended and accompanied by poor
classified according to the direction of airflow     weather, then losses of DM up to 10% of the
through the grain: cross-flow, counter-flow          total crop have been reported.
and concurrent-flow. These driers are nor-              Mechanical treatment of field-mown crops
mally operated by specialist contractors or        using turning and tedding the swath can sub-
installed on large arable farms.                   stantially increase the drying rate. Spreading
                                                   of mown grass within 1 h can increase the
Forage                                             rate of water evaporation by up to five times,
Some drying is essential for the preservation      mainly as a result of water evaporation
of forage crops such as grasses, legumes or        through open stomatal guard cells. Following
whole-crop cereal silage for livestock winter      this time period the stomata will close and
feed. As forage crops mature and the succu-        plant water loss will need to pass through the
lent leafy material is replaced by stem and        thick cell walls.
seed heads, the moisture content will decline
naturally. With grass and legume crops, a fur-
                                                   Barn-drying
ther field curing or wilting of mown crops will
                                                   Barn-drying was popular in the UK during
be required in order to reduce the moisture
                                                   the 1960s, both in methods of ventilation
content and reduce the potential effluent loss
                                                   and in a shift from batch drying to storage
during storage as baled silage or bunker
                                                   drying. However, even at its peak barn-dry-
silage. High moisture (> 80%) of forage crops
                                                   ing accounted for no more than a small pro-
may lead to an undesirable clostridial fermen-
                                                   portion of the total hay crop made in the
tation, which may increase losses and reduce
the feed nutritional value and palatability.       UK and, as field haymaking declined from
Reducing the moisture content of forage            1970 onwards, it was replaced by ensilage.
crops to < 70% will ease the method of trans-      Thus few large-scale units were installed and
portation of harvested crop from field to stor-     most of the limited number of barn-drying
age, with higher levels of dry matter being        installations still operating are likely to be
transported per trailer load. In the UK the        storage driers, holding between 50 and
main method of reducing forage crop mois-          100 t of hay.
ture content is field wilting.
                                                   High-temperature drying
Field wilting                                      High-temperature drying is undoubtedly the
Field wilting of forage crops is the most com-     most efficient method of conserving a green
mon method of reducing moisture content of         forage crop. Total loss of dry matter, from
crops using natural resources of wind and          standing crop to dried product, can be as low
solar energy. Wilting of crops for silage or       as 3%; furthermore, because the crop can be
haymaking requires herbage to be cut with a        cut for drying at a much more immature
mower and left in the field for varying periods     growth stage than is practicable for either
of time prior to lifting and harvesting. In poor   hay or silage, the nutritive value of the dried
weather conditions, dry matter content of          product can be much higher. High-tempera-
crops will increase only slightly and in           ture drying is also largely independent of
extended wilting periods soluble sugars and        weather conditions. Because of this potential,
protein content will be reduced. In contrast,      a considerable programme of research on
during good weather conditions wilting will be     high-temperature drying was conducted dur-
rapid, with minimum losses in soluble sugars       ing the 1960s. Largely as a result of this
and protein content. Under these conditions        research, production of dried grass in the UK
the dry matter content of the crop may             rose from 65,000 t in 1965 to over
exceed 350 g kg 1.                                 200,000 t in 1972, and further major
158                                          Duck




expansion was predicted. However, grass-          and South America and is more closely
drying is based on the burning of fossil fuel,    related to geese than to the domestic duck.
generally oil, to evaporate the water in the      The incubation period for its eggs is 35 days
fresh crop, with up to 300 l of oil being         instead of 28 days for other ducks. Unlike
needed to produce 1 t of dried grass from a       other domesticated drakes, which have
crop cut at 80% moisture content. Sharp           curled feathers on the upper tail, Muscovy
increases in the price of oil during the 1970s    drakes have none. Plumage comes in a
made grass-drying much more expensive and         range of colours but white is most common
greatly reduced the economic benefits of           in commercial production. They prefer to
dried grass as a livestock feed. As a result      graze and have a slightly curved bill to har-
there was a steady fall in the amount of dried    vest grass seeds. They are often used to
grass produced in the UK, down to the pre-        incubate eggs and make excellent mothers.
sent annual level of about 70,000 t. Most of      Body weights of the sexes are quite different,
this is from drying specialized crops such as     drakes weighing about 5–6.5 kg and females
lucerne, with an annual output of more than       2.5–3.5 kg. Crossing the Muscovy drake
5000 t, and the operators who have con-           with the Pekin female gives a mule offspring
tinued in production have remained com-           that is fast-growing with less fat and higher
petitive by wilting the cut crops in the field     lean in the carcass, but sterile. At 63 days
before bringing them to the drying plant,         the male weighs about 4.0 kg with a feed
thus greatly reducing fuel consumption and        conversion ratio (FCR) of 2.6 and a breast
increasing drier output. The situation in the     meat yield of 16%. Growth rate of the
UK contrasts sharply with that in a number        female is 10% lower.
of other EU countries, and since 1980 total          Numerous breeds of duck are used to
EU production has more than doubled, to           produce eggs and meat. Outside Asia, the
4,500,000 t of dried green crop a year,           Khaki Campbell is the most common
mainly as a consequence of EU support for         because of its low body weight and high egg
dried green crops.                         (RJ)   production, often in excess of 300 eggs per
                                                  year. Pekin ducks, traditionally used for
                                                  meat production, are today, through selec-
Key references                                    tion, also prolific layers. In Asia, selection
Nash, M.J. (1985) Crop Conservation and Stor-     has often focused on the ability to forage in
   age in Cool Temperate Climates, 2nd edn.       rice fields. Light-bodied, high-producing
   Pergamon Press, Oxford, UK.                    ducks, such as the Indian Runner and
Raymond, F. and Waltham, R. (1996) Forage Con-    Alabio, stand upright, allowing them to
   servation and Feeding, 5th edn. Farming        move between the rice plants in the tradi-
   Press, Ipswich, UK.                            tional systems (Farrell, 1995). In Taiwan,
                                                  the Brown Tsaiya is the only egg-laying
Duck        Ducks are kept for meat, eggs,        breed; it produces up to 325 eggs per year
feathers and down, and liver fat. Most of the     and weighs 1.5 kg. For meat production,
world duck population (917 million) is found      the White Pekin is the most popular.
in China (636 million), where they were              Ducks, unlike most other avian species, do
domesticated more than 2500 years ago.            not have a distinct crop. Instead, there is a
The domestic duck originates from the             widening of the oesophagus where food sits
green-headed mallard Anas platyrhynchos           temporarily. They feed briefly, then drink
in the tribe Anatini (dabbling ducks) in the      copious amounts, resulting in watery excreta
subfamily Anatinae of the family Anatidae.        (which leads to wet litter problems). Ducks are
There are about 40 species of the genus           hardier than chickens; they are less prone to
Anas.                                             avian diseases, have a high reproductive rate,
   The Muscovy or Barbary duck (Cairina           run in flocks and are easier to manage. Com-
moschata) is not derived from the wild mal-       mon viral diseases are hepatitis, enteritis (duck
lard and belongs to the Cairina tribe (perch-     plague), avian influenza and fowl cholera, a
ing ducks and geese); it is a native of Central   bacterial infection.
                                                  Duck                                             159




    Over the last few years, duck production           Philippines, the ‘balut’, an embryonated egg,
has increased by almost 10% per year, faster           incubated to day 19, is a delicacy. Salted eggs
than any other farmed animal. Of the world’s           and century eggs are traditional methods of
2.9 million metric t annual production of duck         preserving duck eggs, giving them a charac-
meat, China’s contribution was 2 million t, or         teristic taste. In Taiwan, 95% of duck eggs are
69%. Other major producers in South-east               processed in these ways but in Indonesia most
Asia are Thailand, Vietnam and Malaysia.               are eaten fresh.
Roast Pekin duck is a traditional Chinese dish.            Today’s Pekin genotypes of mixed sex can
Other traditional products include smoked              grow to 3.5 kg in 6 weeks with an FCR of
duck, pressed duck and salted duck. In western         about 2.3:1, a carcass yield of 72%, a fat con-
countries, emphasis has been on breast meat            tent of 20%, and breast meat yield of the evis-
yield, reduced fat, and further processing for         cerated carcass of 14–16%. Typical mature
sale as cut portions. France has the highest           body weight is < 5 kg for males and > 4 kg
production in Europe (23,500 t), where there           for females. Until recently, carcass fat of up to
has been emphasis on the Muscovy ducks,                30% was not uncommon in Pekin ducks.
whose meat colour and characteristics are not          Duck meat is substantially more expensive
unlike bovine red meat. Drakes are usually pre-        than chicken meat because of higher costs of
pared in cut-up portions because of their size,        processing, generally poorer FCR and higher
whereas the females are marketed whole.                labour needs.
Liver fat (see Geese) from ducks is a major                Intensive systems may be fully enclosed,
industry in several countries: in France, mule         with straw bedding. Ducks are sometimes
ducks are commonly used for this. Starting at          raised on a slatted floor or wire mesh over a
about 10 weeks of age they are force-fed sev-          pit, or with a mix of bedding and mesh floor
eral times a day for 2 weeks or more, produc-          for the feeders and waterers because ducks
ing livers that weigh 400–700 g.                       tend to defaecate when eating. Adequate
    Duck eggs are not popular in most western          ventilation is essential to remove the ammo-
countries. They contain 30% more fat than              nia in excreta. If they are overcrowded or the
hen eggs, are normally larger, and vary in             diet is inadequate, feather pecking of wing
colour from white to brown to blue-green. In           tips, back and vent is not uncommon. Ducks
Asia, they are eaten in many forms. In the             may have access to an outdoor run, and




Intensive systems for ducks may be fully enclosed, with straw bedding.
160                                           Duck




many producers, especially in Asia, provide        Table 1. Nutrient requirements (g kg 1) of meat-type
them with a pond. Ponds are not essential for      Pekin ducks for starter (1–21 days) and finisher periods
raising ducks, but they may improve feather        (21–49 days) on a total and digestible basis.
production and facilitate mating. In China,                                 Starter           Finisher
ducks are raised in large numbers and invari-
ably with access to water. Laying ducks are        Energy (MJ kg 1)            12.1              12.6
provided with nest boxes with bedding at           Crude protein              220               175
ground level and usually against the back wall                          Total Digestible Total Digestible
of the house.                                      Arginine             12      10       10       7.8
    In traditional systems in Asia, ducks are      Leucine              14               11
herded in rice fields where they scavenge for       Lysine               11.6     9.5       9      7.2
fallen rice grains. In the flooded fields, they      Isoleucine            7       6.8       5      4.9
also feed on snails, fish, insects and small        Methionine            4.4     3.4       3.2    2.9
crustacea and are returned to outside or           Methionine + cystine 8.6      6.7       7.7    5.4
                                                   Tryptophan            2.1               2      1.4
indoor pens at night. They lay their eggs in
                                                   Threonine             7.2     6.2       6.6    5
the early morning before they are released
into the fields. The system has a low cost,
with low inputs and minimum feed supple-               Specifications for Muscovy and mule ducks
mentation. The ducks lay seasonally, produc-       are about 10% less. Mineral and vitamin
ing 60–90 eggs per year.                           requirements of ducks are similar to those of
    Artificial incubation of eggs has caused        broiler chickens except for niacin, for which
difficulties in the past, resulting in low hatch-   the requirement is higher (55 mg vs. 35 mg
ability. Treatment of eggs, pre-incubation,        kg 1). Zinc requirement is slightly higher and
and conditions in the incubator differ from        calcium lower for ducks. The ingredients used
                                                   are the same as for other avian species. Duck-
those for hen eggs. Pekin ducks are not
                                                   lings are highly susceptible to mycotoxins,
good sitters, and in Asia Muscovy ducks are
                                                   which may be a particular problem in ground-
often used to incubate their eggs. There are
                                                   nut meal and maize in the humid tropics.
also ingenious traditional incubating sys-
                                                       Pekin egg-laying ducks are now producing
tems. Some rely entirely on heat from the
                                                   almost as prolifically as commercial hens. For
developing embryos: the eggs are kept on
                                                   maximum production, they are grown to spe-
trays in baskets and are turned twice daily        cific target weights for age so that they come
by hand, resulting in a hatchability of >          into lay at an ideal body weight. There are
85%. Artificial brooding of ducklings lasts         three diets: starter, grower and developer;
for only 10–14 days.                               then two diets, either layer or breeder, which
    For meat production, there may be two or       differ only slightly in that most minerals and
sometimes three diets (0–14 days, 15–35            vitamins are higher in the breeder diet for
days and 36–49 days). The first 2 weeks are         deposition in the egg and the developing
critical. With the rapid progress in breeding      embryo. Shown in Table 2 are the recom-
for growth rate and lean deposition, require-      mendations for some nutrients used by a large
ments for nutrients, particularly for amino        commercial Pekin duck producer for females
acids, have had to be re-examined. Most of         weighing 3 kg, and those of the smaller Khaki
the information on nutrient requirements is        Campbell (1.7 kg) laying a 60 g vs. 80 g egg.
difficult to access. As with other poultry,             Lysine in the layer and breeder diets is
lysine, threonine and methionine are the most      more generous than in diets of commercial
critical amino acids. A fixed relationship has      brown-egg layers, and those specified for
been established between lysine and other          Khaki Campbells. For foie gras production,
amino acids (‘ideal protein’). Shown in Table      wet ground maize, sometimes with fat, is usu-
1 are published specifications for meat-type        ally force-fed. There is some discussion as to
Pekin ducks of a commercial strain. For maxi-      whether a more balanced diet would be more
mum intake, diets should be pelleted, as ducks     appropriate to give better carcass characteris-
do not like powdery feed.                          tics in ducks that are still growing.      (DF)
                                               Dyschondroplasia                                             161




Table 2. Nutrient requirements (g kg 1) for layer ducks during growth and production.

                                  Starter       Grower          Developer        Layer/breeder   Khaki Campbell

Energy (ME MJ kg   1)              11.9           12.1             11.6            11.5              12
Crude protein                     220            175              155             195               180
Lysine                             11              8.5              7              10.0 (8.0)*        7.9
Methionine                          5              4                3               4.0 (3.6)         3.4
Methionine + cystine                8              7                5.5             6.8 (6.4)         6.2
Threonine                           6.9            5.7              4.9             7.0 (5.8)         5.7
Tryptophan                          2.4            2                1.6             2.2 (1.6)         1.7
Calcium                             9              9                9              29                32.5
Phosphorus (available)              5.5            4.2              4               4.5               4.5
Sodium                              1.7            1.6              1.6             1.6               1.8

*Digestible basis.
ME, metabolizable energy.



Key references                                             sured and from this the total mass of nitrogen
Farrell, D.J. (1992) Nutrition and management of           in the sample is calculated. For nutritional
   ducks. In: Wiseman, J. and Garnsworthy, P.S.            studies it is an alternative to the Kjeldahl
   (eds) Recent Developments in Poultry Nutri-             method.                                   (SPL)
   tion 2. Nottingham University Press, Notting-
   ham, UK, pp. 203–226.
Farrell, D.J. (1995) Table egg laying ducks: nutri-        Duodenum          The proximal section of the
   tional requirements and current husbandry sys-          small intestine, between the pylorus and the
   tems in Asia. Poultry and Avian Biology                 jejunum, where digesta leaving the stomach
   Reviews 6(1), 55–69.                                    are mixed with secretions from the pancreatic
Farrell, D.J. and Stapleton, P. (1986) Duck Produc-        and bile ducts.                          (SB)
   tion Science and World Practice. The Univer-
   sity of New England, Armidale, NSW, 430 pp.
Scott, M.L. and Dean, W.F. (1991) Nutrition and
                                                           Dyschondroplasia             Dyschondroplasia
   Management of Ducks. Ml Scott, Ithaca, New              (chondrodystrophy, osteochondrosis) occurs
   York, 177 pp.                                           as a congenital lesion in manganese defi-
                                                           ciency in calves, associated with impaired syn-
Dumas method           A method for meaur-                 thesis of chondroitin sulphate, and seen as
ing the amount of nitrogen in organic com-                 enlarged joints and deformed limbs. Copper
pounds. A weighed amount of sample is                      deficiency with molybdenosis causes over-
mixed with copper(II) oxide and heated in a                growth of epiphyseal cartilage, associated
tube. All nitrogenous compounds present in                 with impaired activity of lysyl oxidase, and
the sample are converted into nitrogen gas,                seen as lameness with obvious swellings, in
which is separated from other gases and col-               calves, foals and deer.                 (WRW)
lected. The volume of nitrogen gas is mea-                 See also: Leg weakness; Manganese
                                               E

Early weaning              Removal of young        the availability of wild juveniles (elvers) return-
mammals from their mother at a time before         ing from the sea.
that which is normal under natural conditions.         Since the optimum temperature for eel
If left undisturbed, piglets will not wean them-   growth is in excess of 20°C, their culture in
selves until 12–16 weeks of age. In farm prac-     temperate climates requires the use of recircu-
tice, the age at weaning can vary widely and       lation systems for most efficient use of heated
the term ‘early weaning’ has different mean-       water. Pond culture is practised in south-east-
ing in different countries. Within the Euro-       ern Asia. Cannibalism and variable growth are
pean Community, animal welfare legislation         also problems in eel culture. About 150,000 t
specifies that weaning may not take place at        of cultured eels are marketed annually, with
less than 3 weeks of age. Commercial wean-         over 90,000 t being consumed in Japan.
ing ages typically vary between 3 and 5            Italy, Japan and China are the major produc-
weeks. However, weaning at much younger            ers of eels.                                 (RHP)
ages is possible and is practised in some coun-
tries as a means of improving both sow out-        Efficiency         of     energy       utilization
put and herd health management. The                Energetic efficiency is defined as the ratio
practice of segregated early weaning involves      between energy output (in useful end-prod-
weaning piglets at 10–18 days of age, whilst       ucts) and the corresponding energy input. It
still protected by maternally derived antibod-     can be obtained from the relationship
ies, and removing them to a clean site, away       between energy balance and metaboliz-
from infectious challenges of the breeding         able energy (ME) intake (see figure). The
herd. The nutritional requirements of the          slope of this line is interpreted as the effi-
piglets depend heavily on the age at weaning.      ciency of energy utilization (k). Historically,
Younger pigs have little experience of eating      the relationship has been represented as hav-
solid food and have an immature digestive          ing two linear segments. Below mainte-
enzyme system. They are very susceptible to        nance, the slope of the line between fasting
enteric disorders and therefore require highly     heat production (FHP) and the metabolizable
digestible diets containing milk products and      energy intake for maintenance (MEm) indi-
cooked cereals.                            (SAE)   cates the efficiency with which dietary nutri-
See also: Piglets                                  ents are used for maintenance purposes,
                                                   relative to mobilizing body reserves for that
Eel        Some species of the freshwater eel      purpose. This relative efficiency has been
family (Anguillidae) are of importance to aqua-    called the efficiency for maintenance (km) and
culture, with the Japanese eel (Anguilla           depends on both the diet and the body
japonica) and the European eel (A. anguilla)       reserves used when the animal is actually fed
being the principal cultured species. The fam-     below maintenance. The slope of the line
ily has a worldwide distribution, with the         above maintenance is the energetic efficiency
greatest number of species in South-east Asia      for production (e.g. growth, lactation). With
and the south-western Pacific, including Aus-       increasing ME intake, growing animals
tralia and New Zealand. All species are            deposit an increasing fraction of energy as
catadromous, living in fresh water but return-     lipid (relative to protein). As the energetic effi-
ing to sea to spawn. The larvae have not been      ciencies of protein and lipid deposition differ,
reared successfully and so all culture relies on   the linear relation is therefore overly simple.

                                                                                                  163
164                               Efficiency of feed conversion (FCE)




                                                                   kproduction
      Energy balance




                                    MEm                                Metabolizable energy intake



                             km


                       FHP



Relation between the energy balance and metabolizable energy intake.



    Because km is a relative efficiency, its value    The theoretical energy expenditure for ATP synthesis
typically exceeds that of the efficiency of pro-      from various substrates.
duction and may even exceed unity. The               Source        kJ mol   1   ATP   Source          kJ mol   1   ATP
maintenance energy requirement is essentially
a requirement for adenosine triphosphate             Glucose            74.0          Phenylalanine      124.0
(ATP). It is difficult to express the efficiency of    Tri-stearin        75.7          Tyrosine           107.0
ATP synthesis as a fraction of energy input          Acetate            87.4          Histidine          149.8
‘retained’ as ATP; nevertheless, the (relative)      Propionate         85.4          Arginine           133.6
                                                     Butyrate           81.2          Serine             116.0
efficiency with which nutrients can be used for
                                                     Lysine            102.2          Glycine            149.2
ATP synthesis can be compared (see table). It        Methionine        129.3          Alanine            104.5
appears that glucose and lipids can be used          Cysteine          178.4          Glutamate           91.8
relatively efficiently for ATP synthesis,             Threonine         100.0          Proline             92.5
whereas volatile fatty acids are used 10–18%         Tryptophan        134.0          Aspartate          103.9
less efficiently. The efficiency of using amino        Isoleucine         88.4          Valine              92.7
acids for ATP synthesis is considerably lower.       Leucine            90.6
Part of this inefficiency is due to the incom-
plete oxidation of amino acids. The nitrogen             In the 20th century, considerable research
of amino acids is excreted as urea, which            has been carried out on the energetic efficiency
involves both a physical loss of energy (as          of fat deposition. In ruminants, a major part of
urea) as well as the energy expenditure to syn-      the energy supply is derived from the end-prod-
thesize it (2 ATP/N).                                ucts of fermentation. The metabolic utilization
    The theoretical efficiency of protein synthe-     of these end-products (and the associated cost
sis is approximately 85% (see Energy costs)          of fermentation) is less efficient than that
but the actual efficiency is often lower, due to      observed in non-ruminant animals. As with the
protein turnover. The efficiency of depositing        efficiency for ATP synthesis, the efficiency for
protein in animal tissue appears to be consid-       fat deposition in non-ruminants increases in the
erably lower (approximately 60%) than that of        order protein, carbohydrate, lipid.     (JvanM)
depositing protein in animal products such as
milk or eggs (75%). Part of this difference may      Efficiency of feed conversion (FCE)
be due to difference in protein turnover             The efficiency of conversion of feed into pro-
between these types of production.                   ductive output (e.g. meat or eggs) is the
                                          Egg composition                                      165




major cost in most animal enterprises and so        egg is approximately 623 kJ 100 g 1 com-
it is often used to indicate the efficiency of       pared with, for example, 776 kJ 100 g 1 for
the system. Efficiency is commonly expressed         the duck’s egg. While the duck’s egg contains
as the weight of productive output divided by       more total lipid than the hen’s egg (13.8 g
the weight of feed eaten (the term ‘gain:feed’      100 g 1 cf. 10.0 g 100 g 1, respectively), the
is also used in growing animals). Differences       amounts of total saturated fatty acids differ
in feed conversion efficiency therefore indi-        only slightly. The amounts of total monosatu-
cate differences in the availability and utiliza-   rated fatty acids are significantly greater in
tion of the feed supplied, the proportion of        duck’s eggs (6.5 g 100 g 1 cf. 3.8 g 100 g 1),
the available nutrients that are required for       with cholesterol levels in the duck’s egg being
body maintenance and the nutrient composi-          more than double those in the hen’s egg (884
tion of the productive output (the ratios of        mg 100 g 1 cf. 425 mg 100 g 1).
protein:lipid:ash). Feed conversion ratio               The albumen in the hen’s egg consists pri-
(feed:gain) is inversely related to FCE             marily of water (on average 88%), the remain-
(gain:feed) and is also used to describe the        der being protein (approximately 10%); lipid,
efficiency of feed utilization.            (SPR)     carbohydrate and ash each account for less
See also: Feed conversion ratio (FCR)               than 1%.
                                                        The fibrous shell membranes are proteina-
Egg composition             The structure of an     ceous and are characterized by high contents
egg can be defined according to the parts of         of histidine, cystine and proline while being
the reproductive tract. Thus the ovaries form       relatively low in glycine.
the yolk, the magnum the albumen, the isth-             The bulk (approximately 98%) of the shell
mus the shell membranes, and the uterus or          is inorganic in nature, being predominantly
shell-gland the shell and cuticle.                  calcium carbonate in the form of calcite. The
    The domestic hen’s egg has a yolk with a        organic matrix accounts for the remainder of
solids content of approximately 50%, of which       the shell. The matrix permeates the shell and
lipid accounts for 31–36%, protein 15–17%,          is linked to the shell membranes via the
carbohydrate 0.2–1.0% and ash 1.1%. The             organic cores that are embedded in the cone
composition of the yolk lipid is approximately      layer. The shell may be capped by either an
66% triglyceride, 29% phospholipid and 5%           organic (e.g. chicken, grouse) or inorganic
cholesterol. The energy content of the hen’s        (e.g. gannet, shag) layer. The glycoprotein




The structure of the egg.
166                                         Egg formation




cover on the shell of the hen’s egg is con-          to release the ovum. The empty follicle, which
structed from spheres (< 1 m) forming an             is anatomically similar to the mammalian cor-
uneven layer some 0–13 m thick. The                  pus luteum, starts to degenerate within a day
spheres are mainly protein (90%), the amino          of ovulation and has disappeared within about
acids having a high glycine content.   (NS)          a week of ovulation. During this time, it pro-
                                                     duces a hormone that plays an important role
Egg formation            At hatch, the left ovary    in controlling the expulsion of the fully formed
of the domestic hen contains several thousand        egg from the vagina at oviposition.
ova, but fewer than 2000–3000 will be ovu-               Within 15 min of its release from the
lated during the bird’s natural productive life.     ovary, the ovum is engulfed by the funnel-
The number of ova recruited into the ovarian         shaped proximal end of the oviduct
hierarchy at any one time is rarely more than        (infundibulum). After a further 15 min, the
ten and more commonly only six to eight.             ovum passes into part of the oviduct called
When ova are in the hierarchy, yellow yolky          the magnum where, over a 3 h period and in
material (vitellin) produced by the liver under      response to mechanical contact with the ovi-
the influence of oestrogen is transferred to the      ducal walls, albumen proteins are deposited
developing follicles so that each ovum               on to it. Moving on to the isthmus, the devel-
increases its weight by about 2 g day 1 over a       oping egg spends the next 1.5 h having fibres
period of 9–10 days. Ovarian follicles have a        extruded on to it which form the inner and
blood supply to most of their surface, with the      outer shell membranes. During the initial 5 h
exception of a narrow avascular strip called         in the uterus or tubular shell gland, the egg is
the stigma. During the final day of follicular        plumped by the accumulation of water and
development, plasma progesterone in the fol-         electrolytes. Additionally, the fibres of the
licular veins rises, stimulating the hypothala-      shell membranes are organized into the
mus to release GnRH, which, in turn,                 mamillary cores that will fix the mineral shell
stimulates the release of luteinizing hormone        to the shell membranes. The egg finally enters
by the anterior pituitary, triggering ovulation.     the shell gland pouch where, over a period of
At ovulation, the follicle splits along the stigma   10–14 h, calcium carbonate crystals are




The stages of egg formation.
                                          Egg production                                       167




deposited to form the shell proper. Calcium        range’, are characterized by larger colony
ions (Ca2+) for shell formation may be from        sizes and the ability of the bird to move freely
the diet, via the upper small intestine blood      within the housing and, for free range, to
system, from a labile form of calcium phos-        access land outside the housing.
phate in medullary bone stores in the long             The type of system used to house the lay-
bones or, in desperate situations, from cortical   ing bird determines in part the bird’s nutri-
bone. In brown-shelled eggs, the pigment por-      tional requirements. The energy requirements
phyrin is secreted in the final 6–10 h of egg       of birds in extensive systems are higher than
formation. Total egg formation time varies         those of birds kept in cages because they are
with lighting regime, age and size of egg, but     more active and, in the case of birds allowed
is generally about 24–25 h.              (PDL)     access to range (especially in northern cli-
                                                   mates), exposure to lower environmental tem-
Egg production           Egg production sys-       perature. As energy requirements influence
tems differ across the world, but there is a       the amount of feed consumed, it is to be antic-
tendency for the larger companies to use           ipated that feed intake is depressed at temper-
cage-based systems for housing hens for egg        atures above the house set temperature and
production, while the smaller companies and        increased at lower temperatures. Energy
home producers use extensive systems.              requirements will also be affected by egg out-
Although domestic hen eggs dominate the            put – an egg contains up to 418 kJ of energy.
world table-egg market, other types of poultry         The protein requirements of the laying hen
are also kept for their eggs. The Indian Run-      vary according to the number of eggs being
ner duck, for example, is kept for its eggs        laid. The percentage protein in the diet
across the world, but particularly in Asia.        increases to a maximum of approximately
Ducks are kept almost exclusively in floor-         19% at peak production and then falls back to
based or free-range systems.                       a pre-laying level that may be only 15%. The
    Cage-based systems first became popular         amino acids that have a significant impact on
for hens because they were perceived to offer      the laying bird are arginine, lysine, methion-
a means of keeping birds in such a way that        ine, cystine and tryptophan. When an imbal-
they had ready access to feed and water while      ance in the amino acid profile occurs it is
being protected from adverse weather condi-        frequently a deficiency in methionine that is
tions, predators and pathogenic organisms.         identified. If the environmental temperature
The rapid development of the cage system           remains elevated for a significant period of
and, in particular, the mechanization that         time, the birds’ feed intake is lower (as dis-
allowed cages to be stacked six or more tiers      cussed above) and the percentage protein in
high, allowed large numbers of birds to be         the diet may need to be increased.
kept in a building with a relatively small floor        Shell quality is a nebulous concept, deter-
area. While egg production from well-run           mined in part by the egg’s end-use (i.e. table,
cage units is very high and the overall mortal-    processing or hatching), but one of the key
ity low, public concerns about the welfare of      nutritional parameters that is cited as being
birds kept in these so-called intensive systems    related to shell quality is the calcium require-
has led in Europe (with similar concerns now       ment. This is to be expected, given that the
being expressed in the USA) to the proposed        shell consists predominantly (98%) of calcium
replacement of the traditional cage system by      carbonate in the form of calcite (cf. aragonite
‘enriched cages’. These cages allow the birds      or vaterite). The calcium and phosphorus
greater freedom of movement; they provide          requirements of the bird change depending on
for dust bathing and perching and have abra-       the number of eggs being laid, the age of the
sive surfaces for keeping the claw at an           birds (calcium uptake becomes less efficient as
acceptable length. Alternative systems of pro-     the bird ages) and the amount of feed being
duction have been increasing in popularity,        consumed (e.g. high temperatures or feed
particularly for the producer who sells eggs       high in energy both depress feed intake).
into a niche market. These more extensive          These factors result in the percentage calcium
systems, which include ‘barn’ and ‘free-           requirement varying from < 2% to > 5%,
168                                          Eggshells




depending on the environment, feed con-            region of the oviduct, immediately prior to the
stituents, age of the bird, stage in the produc-   egg entering the uterus or shell-gland where
tion cycle, etc.                                   the bulk of mineralization takes place over
    Another factor that needs to be taken into     about 18 h. During this period the opportunity
account is the form in which the calcium is        exists for shell formation to be disrupted by a
presented to the bird. Shell formation takes       number of events or conditions.
some 18 h and tends to take place during the           Disease (e.g. infectious bronchitis) or nutri-
hours of darkness, with the egg being laid         tional factors (e.g. high levels of lathyrogens)
soon after the lights are switched on. Calcium     can cause wrinkled shells. The wrinkled shell
should be provided, therefore, in a form that      results from either the failure of the shell
can be resorbed by the bird during the hours       membranes, which form the foundation for
of darkness, when the bird is unlikely to be       the shell, to tension correctly during plumping
eating. If calcium is provided as a finely          (e.g. as caused by infectious bronchitis) or the
ground powder it is likely to pass rapidly         structure of the membranes being perturbed
through the gizzard and be unavailable to the      (e.g. as caused by lathyrogens). The normally
bird at the time when it needs it most. For this   smooth texture of the shell results from the
reason the majority of the calcium should be       distinct outer layer of the shell (surface crystal
provided as coarsely ground limestone or oys-      layer) being overlaid by an organic layer – the
ter shell. Laying birds will, if the demand for    so-called cuticle.
calcium is high (as in high-output lines of lay-       If the bird is stressed it is possible that the
ing hens), supplement dietary calcium with         egg can be expelled from the oviduct before
calcium that has first been incorporated into       the mineralization process has been com-
the labile cortical bone. Cortical bone will be    pleted. The resultant partially formed shell
maintained at the expense of the less labile       will, depending on its thickness, feel rough
medullary bone if the demand for shell cal-        when compared with normal shells, mineral-
cium is constant. Eventually this will cause so-   ization having proceeded as far as the forma-
called ‘cage layer fatigue’ and the associated     tion of the cone or palisade layers. Also,
increase in bone breaks reported in high-out-      where mineralization has not proceeded
put flocks.                                         beyond the fusion of the cone tips, the shell
    Phosphorus is not incorporated into the        will be flexible: the form and strength are pro-
shell in any significant amount but, because of     vided by the shell membranes and influenced
its role in bone biology, its inclusion in diets   by the underlying albumen.
can affect shell quality. Recommended daily            The presence of two eggs in the oviduct at
intakes of available phosphorus in layer           the same time can also cause thin-shelled
rations are in the order of 400–450 mg. It is      eggs. If both eggs arrive at the same time in
important to note that this figure refers to        the oviduct they will have equally thin shells,
available phosphorus, as some 40% of phos-         but if one arrives much earlier than the other
phorus in a laying-hen diet is present as phy-     it will have all, or almost all, of its full comple-
tate, a bound organic form that is difficult for    ment of calcium carbonate while the other
the bird to access.                                egg will have little or no shell. In the former
    It is common practice to feed pigments to      circumstance the eggs will have a ‘slab-sided’
laying hens in order to provide the consumer       appearance caused by the two eggs pressing
with eggs that have a yolk of a consistent         against each other in the shell gland.
colour, irrespective of the hen that laid the          So-called equatorial or shoulder bulges
egg or the point in the production cycle.          (where the shell has a thickened appearance
                                            (NS)   around the equator) are the result of the shell
See also: Egg composition; Egg formation;          being broken around the equator during the
Eggshells; Eggs                                    early stages of mineralization. Typically this is
                                                   caused by the bird being stressed; the conse-
Eggshells       Eggshells consist primarily of     quent constriction of the oviduct results in the
calcium carbonate in the form of calcite. Shell    shell being broken. The crystalline calcium
mineralization commences in the isthmus            carbonate shell is formed by a process known
                                              Elastase                                           169




as epitaxis. Thus the existing crystal face dic-    Eicosanoids           A group of physiological
tates the crystal form. If the mineralizing face    substances derived from 20-carbon unsaturated
is disrupted, as occurs when the shell is bro-      fatty acids. The source of the fatty acids for the
ken, subsequent mineralization will take place      biosynthesis of these compounds is from the
on an uneven surface, both physically and in        two position of membrane phosphatidylcholine.
terms of activation energy, causing the uncon-      Eicosanoids are classified as prostaglandins,
trolled and irregular deposition of calcite.        thromboxanes, leukotrienes and lipoxins.
    Mineralization in the shell gland is termi-     They are local hormones and act through cell
nated in part by a rise in the concentration of     membrane receptors and signal transduction to
phosphate; however, if stressed, the bird may       elicit cellular change. Two pathways are
secrete excess phosphate into the shell-gland,      involved in their synthesis: the cyclooxygenase
causing calcium phosphate to be deposited as        pathway results in the production of
a ‘white dusting’ or ‘splashing’ over the sur-      prostaglandins and thromboxanes; and the
face of the shell.                           (NS)   lipoxygenase pathway produces leukotrienes
                                                    and lipoxins. Dihomo- -linolenic acid (eicosatri-
Eggs          As a source of nutrients the egg      enoic acid, 8,11,14) gives rise to a series of
presents the consumer with a number of ben-         prostaglandins, thromboxanes and leukotrienes.
efits over many other foods. Eggs are rich in        Arachidonic acid (eicosatetraenoic acid,
balanced proteins (with a biological value of         5,8,11,14) gives rise to a separate series of

93.7%) and are a good source of unsaturated         prostaglandins, thromboxanes and leukotrienes
fatty acids, vitamins A, B, D, E and K, iron,       and lipoxins. Finally -linolenic acid, after being
phosphorus and trace minerals. Concerns             converted to a 20-carbon unsaturated fatty acid
about the effect on blood cholesterol of eating     (eicosapentaenoic 5,8,11,14,17), gives rise to a
eggs are now considered to have been over-          separate series of prostaglandins, thromboxanes
emphasized: dietary cholesterol intake has lit-     and leukotrienes. These compounds are potent
tle effect on plasma cholesterol levels in          and can have physiological effects at concentra-
healthy individuals.                                tions as low as 1 ng ml 1.                   (NJB)
    Cooking may destroy some nutrients or
can enhance nutrient availability. Thus             Eicosapentaenoic acid            A 20-carbon
riboflavin levels have been shown to be              fatty acid with five double bonds (C20:5
reduced by up to 20% by some forms of                 5,8,11,14,17), a member of the n-3 family. It

cooking. While unlikely to have a significant        can be formed from -linolenic acid (C18:3
impact in healthy adults eating a balanced            9,12,15) by 2-carbon elongation and desatu-

diet, the egg proteins ovomucoid and ovoin-         ration and is involved in production of
hibitor have been shown to be have anti-tryp-       prostanoids via the cyclooxygenase pathway
tic activity. Similarly the protein avidin binds    and leukotrienes by the lipoxygenase path-
to biotin making in unavailable. Heat treat-        way.                                    (NJB)
ment can destroy these anti-nutritive factors       See also: Eicosanoids
and thus release vitamins, improving their
availability.                                       Elaidic acid      An 18-carbon unsaturated
    Eggs are used in foods not only for their       fatty   acid,   CH3·(CH2)7·CH=CH·(CH2)7
nutritive value but also for their functional       ·COOH, the trans form of oleic acid, the
properties. The albumen proteins allow eggs         form encountered in nature.          (NJB)
to be used as coagulators (e.g. in custards,
scrambled egg) and foaming agents (e.g. in          Elastase         An endopeptidase (pancreato-
cakes, meringues) while the yolk is used            peptidase E; EC 3.4.21.36) that hydrolyses
extensively as an emulsifying agent in, say,        those peptide bonds that involve neutral
batter, mayonnaise and salad dressings. The         amino acids: it is particularly active on elastin.
yolks may also be used as colorants; for exam-      It is secreted from the pancreas as the precur-
ple, the xanthophylls provide the pale golden       sor proelastase, which is activated in the duo-
colour associated with cakes and pasta. (NS)        denum by trypsin.                            (SB)
170                                                Electrolytes




Electrolytes         Soluble ions in body fluids.           Endocrine glands            Ductless glands that
Electrolytes participate in maintaining electro-           secrete hormones into the bloodstream.
chemical gradients and osmotic pressure.                   Unique hormones are released by each of the
Sodium, potassium, magnesium and calcium                   endocrine glands. The pineal gland is in the
are the major cations and chloride, phosphate,             brain near the third ventricle, and the pituitary
bicarbonate, organic acids and protein the                 is in the brain near the base of the skull. The
major anions. Sodium is the major extracellular            thymus is at the base of the neck near the
cation; potassium and magnesium are the                    heart and the thyroid lies on each side of the
major intracellular cations. Phosphate, proteins           trachea. There are two parathyroids, on the
and bicarbonate make up the majority of the                left and right sides of the trachea, next to the
intracellular anions. It is the unequal distribution       thyroid. The two adrenal glands are located
of ions across cellular membranes that gener-              above the kidneys and the pancreas is located
ates electrochemical potentials and the osmotic            near the liver. The two ovaries are located in
pressure required for cells to function.       (NJB)       the lower abdomen, while the two testes are
                                                           normally outside the body in the scrotum.
Embden–Meyerhof pathway: see Glycolysis                                                               (NJB)

Embryonic development: see Fetal growth                    Endogenous protein              Endogenous pro-
                                                           tein comprises all non-dietary nitrogen (N)
Emulsifier         A substance used to stabilize            compounds entering the lumen of the diges-
an emulsion, in animal feeding most com-                   tive tract. These N compounds include
monly to make a liquid mixture of fat and                  enzymes, the glycoproteins of saliva, gastric
water. The table gives emulsifiers that are listed          juice, bile and pancreatic secretions and
in the Feedingstuffs (UK) Regulations 2000.                mucus (mucopolysaccharides) secreted from
                                                           the mucus cells throughout the intestinal tract.
Emulsifier                                   E number       The largest component is contributed by
                                                           desquamated intestinal cells, which can
Lecithins                                   E322
                                                           amount to 30–60% of the total protein that
Propylene glycol alginate                   E405
D-Glucitol                                  E420
                                                           enters the intestinal lumen. Trypsin is the
Mannitol                                    E421           most abundant of the pancreatic enzymes,
Glycerol                                    E422           and proteases the most abundant class of
Sodium, potassium and calcium salts of                     enzymes. Urea is an important non-protein
  edible fatty acids                        E470           component of endogenous nitrogen.
Monoacyl and diacylglycerols                E471               Most endogenous proteins are digested by
Esterified monoacyl and diacylglycerols      E472           pancreatic proteases and are processed identi-
Sucrose esters of fatty acids               E473           cally to dietary proteins. A few proteins (e.g.
Mixture of sucrose esters and monoacyl                     intrinsic factor that is necessary for absorption
  and diacylglyerols                        E474
                                                           of B12 in the ileum) largely escape luminal
Polyglycerol esters of non-polymerized
  edible fats                               E475           digestion.
Propylene glycol esters of fatty acids      E477               Generally, most of the endogenous protein
Stearoyl-2-lactylic acid                    E480           from the stomach and small intestine is reab-
Sodium stearoyl-2-lactylic acid             E481           sorbed (at least 0.65–0.75) in the ileum. Most
Calcium stearoyl-2-lactylic acid            E482           unreabsorbed endogenous protein is con-
Stearyl tartrateq                           E483           verted to microbial protein, some in the ileum
Glycerol poly(ethylene glycol)ricinoleate   E484           but more in the large intestine. N from fer-
Dextrans                                    E486           mented endogenous protein utilized for
Sorbitan monostearate                       E491           energy by the bacteria is either incorporated
Sorbitan tristearate                        E492
                                                           into microbial protein or absorbed as ammo-
Sorbitan monolaurate                        E493
Sorbitan mono-oleate                        E494
                                                           nia in the hindgut, increasing apparent overall
Sorbitan monopalmitate                      E495           N digestibility.
                                                               Endogenous protein loss changes with feed
                                               (MG)        intake and, in feed evaluation, it is practical to
                                              Endotoxins                                        171




express endogenous protein loss in relation to       Endopeptidase           A proteolytic enzyme
the dietary intake, i.e. in g kg 1 dry matter        that has the capacity to hydrolyse internal
(DM) intake. The amount and amino acid com-          peptide bonds in a protein, in contrast to an
position of endogenous protein is influenced          exopeptidase, which hydrolyses terminal pep-
by a number of dietary factors, in particular        tide bonds. Important endopeptidases in the
fibre and antinutritional factors (ANFs). In          digestive tract include pepsin and rennin in
the pig, endogenous protein losses from the          gastric secretions, enterokinase from duodenal
ileum vary from less than 10 to more than 30         epithelial cells and trypsin, chymotrypsin and
g kg 1 DM intake. Endogenous losses in the           elastase from the pancreas.                (SB)
faeces are smaller and less variable.
    Endogenous protein can be considered to          Endorphins          Peptides produced by the
be composed of two fractions: a minimal              brain and having a morphine-like effect. They
(basal) loss and a feed-specific (extra) loss,        are part of the pro-opiomelanocortin peptide
mainly resulting from the effects of dietary         family and are derived from the 31-amino-
protein, fibre and ANFs. The total loss (ileal or     acid carboxyl terminal of the 91-amino-acid
faecal) can be measured after a preliminary            -lipotropin. -Endorphin contains the full
labelling of the experimental animals with 15N       31-amino-acid sequence; - and -endorphins
and measuring the dilution of dietary 14N in         have 15 and 14 amino acids, respectively.
the digesta or faeces by comparing the               Endorphins bind to the same receptors as do
15N:14N ratio in the digesta or faeces with          opiates and play a role in pain perception.
that of the blood. The basal loss can be mea-                                                 (NJB)
sured by feeding N-free diets (or diets with
100% digestible protein at ileal level) that do      Endosperm          In angiosperm seeds, the
                                                     tissue that surrounds the embryo. The
not contain fibre or ANFs.
                                                     endosperm and embryo together comprise
    Endogenous protein loss has a significant
                                                     the inside of cereal grains, with the
influence on experimentally determined values
                                                     endosperm forming the major component.
for the digestibility of protein and amino
                                                     Starch and protein stored within the
acids. Their digestibility is now commonly
                                                     endosperm support the initial growth of the
measured at the terminal ileum because
                                                     germinating    embryo.     The     endosperm
amino acids are practically not absorbed in
                                                     accounts for the nutritional and economic
the large intestine but are metabolized by the
                                                     importance of cereal grains and oilseeds.
microflora which change the amount and
                                                                                               (ED)
composition of the resulting protein that
                                                     See also: Cereals; Grain
appears in faeces. Correction for the basal
endogenous losses of amino acids is now
                                                     Endotoxaemia           The presence of endo-
commonly used for the calculation of true or
                                                     toxins in the blood. This generally occurs with
standardized ileal digestibility of amino acids.     the proliferation of Gram-negative bacteria,
Endogenous protein in the ileal digesta of           such as that seen with Escherichia coli masti-
growing pigs has a characteristic amino acid         tis. Endotoxins are highly inflammatory and
composition, with a relatively low contribution      pyrogenic and result in massive increases in
of most essential amino acids (except threo-         vascular permeability. A common result of
nine, cystine and tryptophan) compared with          endotoxaemia is loss of circulating blood vol-
ideal protein.                                (SB)   ume and loss of cardiovascular function
See also: Protein digestibility; Protein digestion   (shock).                                 (BLS)

                                                     Endotoxins        Heat-stable bacterial toxins
Further reading
                                                     produced primarily by Gram-negative bacte-
Boisen, S. and Moughan, P.J. (1996) Dietary influ-
   ences on endogenous ileal protein and amino       ria. They are included in the bacterial
   acid loss in the pig – a review. Acta Agricul-    lipopolysaccharide cell wall. Endotoxins are
   turae Scandinavica, Sect. A, Animal Science       highly pyrogenic and cause extensive
   46, 154–164.                                      increases in vascular permeability. They are
172                                          Energy




similar regardless of the species of bacteria     a given level of power is consumed for a spec-
and have similar activity and pathogenicity.      ified time; thermal definitions of energy relate
                                          (BLS)   to the heat required to increase the tempera-
                                                  ture of a mass of water by one degree. All
Energy          The capacity to do work.          energy units are precisely related to one
Energy exists in many forms, including chemi-     another and some useful conversion factors
cal energy, mechanical energy and heat. On        include the following.
earth, the primary source of energy is the            1 joule (J) = 1 watt second (W s) = 0.239
sun. Solar radiation warms up the atmos-              calories (cal)
phere and surface of the planet and some of           1 kilojoule (kJ) = 0.278 watt hours (W h) =
it is absorbed by chlorophyll in growing plants       0.239 kilocalories (kcal)
to synthesize organic material from carbon            1 megajoule (MJ) = 0.278 kilowatt hours
dioxide and water. This process, photosynthe-         (kW h)
sis, stores energy in chemical form as plant          1 calorie = 4.184 joules (J)
tissue. The chemical energy of plants may in          1 kilocalorie (kcal) = 4.184 kilojoules (kJ) =
turn be used in the short term as fuel for fires       1.162 watt hours (W h)
or as food for humans and animals, or it may                                               (JAMcL)
be stored over millennia, building up reserves    See also: Energy balance; Energy costs;
of fossil fuel. Metabolism of food makes          Energy metabolism; Energy units; Energy uti-
energy available for the maintenance of           lization; International units
essential body functions, such as respiration
and circulation of the blood, and for growth.     Energy balance            The principle of con-
Metabolism is an oxidative process in which       servation of energy necessitates that food
carbon from the food is combined with atmos-      energy intake is balanced by energy retained
pheric oxygen, with the release of energy as      or lost. The partition of the gross (chemical)
heat, but the total amount of heat or energy      energy of food into its major subdivisions is
produced from the oxidation of any food           illustrated in the figure. Some food is undi-
material is very nearly the same whether it is    gested, resulting in loss of energy as faeces.
burned quickly or digested in the body. It may    The difference between the energy content of
not be identical, because the final state (tem-    the food and the energy content of the faeces
perature and pressure) of the products of the     is termed the apparently digested energy; the
reaction may differ between the two               adjective ‘apparently’ being included because
processes.                                        some faecal material is not of immediate
     In the body, some of the energy of food is   dietary origin but consists of cells or secretions
converted into other forms of chemical            of the alimentary tract. Cellulose and other
energy (body growth, milk, eggs, etc.) and by     complex food constituents that are not sus-
draught animals into mechanical energy, but a     ceptible to digestion by the animal’s own
high proportion of the total energy intake is     digestive enzymes are converted into
returned to the environment as heat or as the     digestible end-products by bacterial fermenta-
residual chemical energy of excreta. Even         tion especially in the rumen, but also in the
mechanical energy is rarely retained in a use-    gut of all species. This results in the produc-
ful retrievable form, but lost as heat in over-   tion and expulsion of combustible gases
coming, say, the friction of a plough or          methane and, to a lesser extent, hydrogen.
cartwheels; an exception is when animal           The digestible energy consists of nutrients
power is used to raise loads, such as water out   that are absorbed from the gut. Waste prod-
of a well.                                        ucts from their further metabolism are lost as
     Because of its many diverse forms, energy    energy excreted in urine; the remaining
may be measured in a variety of units.            energy is the metabolizable energy of the
Mechanical energy is defined in terms of the       food. It has to provide for the energy require-
energy expended when a mass of material is        ments of the body. Firstly, there is the basal
moved a given distance against a specified         energy requirement for maintenance of respi-
force; electrical energy is that expended when    ration, blood circulation and other vital func-
                                             Energy balance                                       173




                         Gross energy
                            of food

                                                                 Energy of
                                                                  faeces

                      Apparently digested
                           energy

                                                              Energy of urine
                                                               and methane

                         Metabolizable
                            energy

                                                                    HEAT
                                                              i.e. basal energy
                                                                 + energy of
                                                                    activity
                                                              + heat increment
                                                                  of feeding

                                                                Retrievable
                                                                   work

                        Retained energy
                        i.e. growth, milk,
                           eggs, wool,
                            fetus, etc.



tions. The minimal rate of energy utilization        body function and activity is non-chemical and
by a resting animal in a comfortable environ-        is generally converted into heat. In most
ment is known as the basal metabolic rate; to        forms of exercise, mechanical work (like the
this must be added the extra energy cost that        work involved in vital body functions) is trans-
occurs after taking a meal (the heat incre-          formed into heat in the course of its execu-
ment of feeding) and any additional energy           tion. The rate at which metabolic heat is
required for activity, thermoregulation or           produced in the body is known as the meta-
other muscular work. Any metabolizable               bolic rate or as the rate of heat production.
energy left over from meeting these demands               In accordance with the principle of conser-
may be retained in the body as new tissue            vation of energy, the heat balance equation
growth or used for the production of milk,           may be written as follows:
wool or eggs.                                             Gross energy of food = energy of faeces
    If the metabolizable energy of the food is                                     energy of urine
insufficient to meet the demand, energy reten-                                      energy of
tion can be negative and the body consumes                                          methane
its own energy reserves. Normally the level of                                     retained energy
food intake is regulated to meet the demands                                       retrievable
of maintenance plus growth in the young, or                                         mechanical work
production in the pregnant or feeding mother;                                      heat production.
otherwise excess food intake leads to the            It is possible, with varying degrees of difficulty,
deposition of body fat. Conversely, a defi-           to measure all of these energy components in
ciency leads eventually to emaciation.               a living animal. Food, faeces and urine may
    The gross energy of food, the energy             be collected and sampled; their energy con-
retained in the body and the energy of faeces,       tents can then be measured using a bomb
urine and combustible gases are all forms of         calorimeter. Heat production can be measured
chemical energy. The energy concerned with           by one of the techniques of calorimetry.
174                                         Energy content




Using indirect calorimetry by enclosing the          the ATP utilized for the resynthesis of triacyl-
animal in a respiration chamber or by employ-        glycerides from fatty acids and glycerol.
ing a mask technique, heat production is cal-            The efficiencies mentioned above are
culated very accurately from the rates of            based on the minimal costs of converting one
oxygen consumption and carbon dioxide pro-           nutrient to another. Other costs (i.e. related to
duction. The energy loss as combustible gases        digestion, absorption and transport) are not
can also be measured in a respiration cham-          specifically accounted for but are included in
ber. Energy retention can be measured using          experimental values of efficiency. For exam-
the carbon and nitrogen balance method,              ple, after a meal, part of the digested energy
or by the difference between metabolizable           is stored (temporarily) as glycogen in the mus-
energy and heat production.                          cle or liver. Depending on how the energy of
    In addition to the overall energy balance,       glycogen is recovered, this temporary storage
there must also be a balance between the             of glucose is associated with an additional
rates of heat production and heat loss, other-       energy cost of 3–5%. Likewise, animals may
wise body temperature alters. Healthy warm-          store energy as body lipid, which may be used
blooded animals usually have an efficient             later for ATP synthesis. Baldwin (1995) calcu-
thermoregulatory system for maintaining deep         lated that storing glucose temporarily as fat is
body temperature within close limits but alter-      associated with an additional energy cost of
ations in the temperature of regions close to        23%. Apparently, this is the price paid for
the skin surface and in the limbs can be con-        storing energy in a very compact form.
siderable, resulting in some storage of heat.            Protein turnover (i.e. the repeated synthe-
The rate of heat loss by an animal can be            sis and hydrolysis of peptide bonds) also rep-
measured in a direct calorimeter. When a             resents a considerable energy cost. If it is
direct animal calorimeter also has a facility for    assumed that 100 g of protein is the equiva-
indirect measurements, it is possible to mea-        lent of 1 mol of amino acids and that five ATP
sure the differences between rates of heat           (from glucose) are required for protein synthe-
production and loss and to relate these to           sis, the maximum efficiency is 2380/(2380 +
changes in body temperatures.          (JAMcL)       5 74) = 87%. Using sources other than glu-
See also: Heat balance                               cose for ATP further reduces the efficiency of
                                                     protein deposition. One additional cycle of
Energy content: see Energy value                     degradation and synthesis requires (at least)
                                                     another five ATP, thereby reducing the effi-
Energy costs         It is difficult to give a pre-   ciency to 76%. The value of kp derived from
cise estimate for the energy cost of mainte-         experiments (approximately 60% for protein
nance functions. According to Baldwin                deposition in growth) suggests that consider-
(1995), nervous tissues contribute 15–20% to         ably more ATP is required. The extent of pro-
the maintenance energy requirement and               tein turnover is affected by several factors.
protein turnover 10–15%; Na+ resorption              Visceral organs (especially the gastrointestinal
by the kidneys, heart function and respiration       tract, liver and kidneys) contribute to protein
contribute 6–11% each. Part of the energy            turnover and to the overall energy expendi-
cost is due to the utilization of adenosine          ture. There are also indications that dietary
triphosphate (ATP) for physiological func-           protein increases protein turnover.      (JvanM)
tions; another part is related to an inevitable      See also: Efficiency of energy utilization
loss of energy (as heat) in the biochemical
transformation of dietary nutrients to ATP and
animal products. For example, when glucose           Key reference
is used, 81% of the energy input can be con-         Baldwin, R.L. (1995) Modelling Ruminant Diges-
served as lipid. However, as ATP is formed              tion and Metabolism. Chapman & Hall, Lon-
during this synthesis, the overall efficiency is         don, 578 pp.
slightly higher (84%). Theoretically, the effi-
ciency of using dietary lipid for lipid deposi-      Energy deprivation: see Starvation; Under-
tion exceeds 97%. The only cost involved is          nutrition
                                            Energy intake                                        175




Energy        expenditure         Synonymous         nants. Poultry, particularly broilers, consume
with heat production. That part of the               up to 10% more energy as pelleted feed com-
metabolized energy which is not productively         pared with mash. Energy intake is also
retained as growth, milk, eggs, etc., but is lost    affected by environmental temperature: at
as heat.                               (JAMcL)       low temperatures (outside the thermoneutral
                                                     zone) energy intake tends to increase to cover
Energy intake             Energy intake is a         the additional heat loss incurred. The opposite
function of species, breed, body mass, age,          effect occurs at high temperatures, as the ani-
physiological state, the form and composi-           mal has difficulty in disposing of the heat
tion of the diet and environmental factors.          increment arising from metabolism of feed.
Energy intake can be expressed in terms of           Domestic fowl have a poorly defined ther-
gross, digestible, metabolizable or net              moneutral zone and energy intake tends to
energy. Because of the relatively wide differ-       increase linearly with falling temperature
ences in digestibility coefficients of feeds,         below 30°C. Within the range 15–30°C the
particularly for ruminants, it is generally          reduction in intake per °C increase in temper-
preferable to express energy intakes as              ature averages approximately 1.6%.
digestible energy (DE) or metabolizable                 Other environmental factors that affect
energy (ME) intake, both of which are rea-           energy intake include feed accessibility, trough
sonably easy to measure.                             design and group size. Pigs in groups tend to
    One way of describing energy intake is in        consume 10–15% less energy than those
terms of multiples of the maintenance                housed singly and large group size and limited
energy requirement, i.e. the amount of               trough space further reduce energy intake.
energy needed to maintain zero energy bal-           Large differences in intake between individual
ance. Growing pigs and high-producing lactat-        animals under uniform conditions have been
ing cows and sows can consume up to about            reported in several studies. For example, the
3 times maintenance (3 M), whereas egg-              average DE intake of pigs over the liveweight
laying breeds of domestic poultry voluntarily        range 35–90 kg was 28 MJ day 1 but individ-
consume about 1.5 M and mature non-lactating         ual intakes varied from 20 to 38 MJ day 1.
animals tend to consume between 1 and                   Under normal production conditions cattle
1.5 M. Whilst energy intake increases as body        are usually encouraged to maximize energy
weight increases, the response is not linear.        intake and this applies, in most cases, to pig
With pigs, for example, a study on individually      and poultry meat production. However, sows
fed growing boars from 20 to 300 kg showed           are normally restricted during gestation to
that DE intake (MJ day 1) was 4.0 W0.5 but           about 26 MJ DE day 1 to avoid excessive
some studies have erroneously concluded that         weight gain and maintain fecundity. After
intakes peak around 100 kg liveweight and            peak egg production it is usually desirable to
subsequently decline. Similar results to those       restrict laying hens to approximately 1.2 MJ
for the boars have been reported for sheep           ME day 1 to maximize feed efficiency. Broiler
fed very highly digestible diets. Animals tend       breeders have to be restricted during growth
to eat to a predetermined energy ‘ceiling’           and the laying cycle to prevent leg and fertility
unless there is a physical limitation to intake,     problems.                              (KJMcC)
such as low digestibility of the feed. Such a sit-   See also: Environment–nutrition interactions;
uation is more likely with ruminants on high-        Voluntary food intake
forage diets. With non-ruminants, increasing
the energy content of the feed tends to reduce
dry matter intake but energy intake tends to         Key references
                                                     Agricultural Research Council (1975) The Nutrient
increase. For example, a 10% increase in
                                                        Requirements of Farm Livestock. No. 1: Poul-
energy content of a broiler diet gives approxi-         try. Burt & Son, Bedford, UK.
mately a 5% increase in energy intake.               Agricultural Research Council (1980) The Nutrient
    Energy intake is also affected by the physi-        Requirements of Ruminant Livestock. Com-
cal form of the feed; for example, chop length          monwealth Agricultural Bureaux, Farnham
of forage affects the voluntary intake of rumi-         Royal, UK.
176                                      Energy metabolism




Agricultural Research Council (1981) The Nutrient   and quantitatively large methods of energy
   Requirements of Pigs. Commonwealth Agricul-      storage and de-storage.
   tural Bureaux, Farnham Royal, UK.                    The metabolizable energy is available to
AFRC (1993) Energy and Protein Requirements         promote synthesis of body tissue (meat or
   of Ruminants. CAB International, Wallingford,    fetus), milk, wool or eggs; it can also be used
   UK.
                                                    by draught animals to do mechanical work. A
                                                    large proportion is transformed into heat that
Energy metabolism              All the energy       is lost to the environment. The level at which
exchanges that occur in a living animal or cell.    metabolism proceeds is determined by both
They originate from the chemical energy of          energy requirement and the availability of
food, which is the prime source of energy for       food. A minimal energy level (basal metabo-
all body processes and activities, including        lism) is needed to maintain essential body
growth.                                             functions such as respiration and blood circu-
    Only part of the chemical energy of food        lation. Eating itself involves further energy
can be utilized in the body; some food con-         expenditure in finding, chewing and absorbing
stituents can be assimilated immediately            the food (known as the heat increment of
through the intestinal walls into the blood-        feeding). Additional energy is required for
stream; some have first to undergo chemical          activity and mechanical work. Only after these
transformation in the gastrointestinal tract        requirements have been met is excess metab-
into a more digestible form; some are totally       olized energy available for retention in the
indigestible. Indigestible and waste by-prod-       body as growth or production (milk, eggs,
ucts are voided as faeces and urine. In all         wool or fetus). Production rates are generally
species, but especially in herbivorous animals,     increased up to a certain limit by additional
which pre-digest food by fermentation in the        food intake. Production and skeletal growth in
rumen, a further waste product is methane.          the young, however, do not cease if food
The remaining energy is metabolizable               intake is insufficient, but proceed by catabo-
energy, which is involved in many chemical          lism of body reserves, mainly fat.
transformations in the organs of the body.              All metabolized energy not retained for
This part of the process is termed intermedi-       production, growth or retrievable work is con-
ate metabolism. It includes some reactions          verted into heat. In warm environments, most
that build up energy-rich compounds                 of the heat produced is wasted and animals
(anabolism) and others that break down              have to find means to get rid of the excess
energy-rich compounds to release energy             heat to the environment. Conversely, in cold
(catabolism). Anabolic and catabolic processes      environments, heat is useful to the animal;
are continuous and simultaneous, with an            indeed in very cold environments animals may
equilibrium between them. A prime example           be forced to metabolize additional food
is the energy-rich compound adenosine               energy simply in order to keep warm.
triphosphate (ATP), which can release                                                      (JAMcL)
energy on being reduced to adenosine diphos-
phate (ADP). Such compounds may be used             Energy requirements               In a ther-
to provide energy quickly at high rates for,        moneutral environment, the energy require-
say, muscular movement, the energy store            ment of an animal is the sum of the energy
being replenished later by reconversion of          retained in animal products and the associated
ADP to ATP, this being coupled to the oxida-        adenosine triphosphate (ATP) costs (i.e.
tion of food-derived nutrients that provide the     the cost of ingestion, digestion and metabo-
energy required. This is an example of short-       lism). The energy content of secreted animal
term energy storage; such temporary storage         products (e.g. milk or eggs) can be determined
is quantitatively small in comparison with the      relatively easily in a bomb calorimeter,
overall level of energy metabolism. In a wider      whereas the energy retained by the animal
sense, growth is an anabolic process and con-       (e.g. growth or gestation) requires a compar-
sumption of body fat during undernourish-           ative slaughter technique or (indirect)
ment is a catabolic one; these are long-term        calorimetry. It is virtually impossible to
                                        Energy requirements                                     177




determine directly the ATP required for physi-      ered part of the maintenance energy require-
ological processes. The main problem is that        ment and may represent an important frac-
energy is released as heat during the transfor-     tion of it. In a comparison between species,
mation of nutrients to ATP as well as during        the cost of activity (kJ kg 1 BW0.75) has been
the actual ATP utilization. Consequently,           found to range from 2.4 (rats) to 30 (pigs) per
energy requirements are expressed in terms          100 min of standing. The heat generated in
of energy, such as metabolizable or net             metabolic processes is usually sufficient to
energy.                                             maintain a constant body temperature but ani-
                                                    mals in cold environments may need to
                                                    divert energy from productive processes to
Maintenance                                         thermogenesis in order to maintain a constant
The maintenance energy requirement is               body temperature. In that case, the energy
defined as the energy requirement of a non-          requirement of the animal includes all the heat
producing animal (i.e. no production of milk,       that is produced (i.e. the ME intake).
eggs or wool, no fetal growth and no net
deposition of body protein or lipid). In addi-
tion, it is assumed that the animal is healthy      Weight gain (protein and fat deposition)
and is kept in a thermoneutral and stress-free      Most of the energy gain in farm animals is
environment. Physiological components of            retained as protein and lipid. Although glyco-
maintenance include blood circulation, nutri-       gen is important for the short-term storage of
ent transport and absorption, respiration,          energy, it plays a minor role in the long-term
excretion and tissue turnover that is unrelated     energetics of gain. The energy requirement
to production. Although there is general            for body weight gain depends on the protein
agreement on the conceptual and qualitative         and lipid composition of the gain. The gross
description of maintenance, it is more difficult     energy values of body protein and lipid are
to quantify maintenance unambiguously in            approximately 23.7 and 39.8 kJ g 1, respec-
farm animals. During fasting, animals catabo-       tively. Although these values can be used to
lize body reserves in order to supply ATP for       calculate the energy content of body weight
essential body functions and so fasting heat        gain, they do not reflect the energy cost of
production is often used as an indicator of the     gain. The latter also includes the cost of nutri-
maintenance requirement; however, it is an          ent absorption, transport and metabolism.
indirect measurement because the efficiency          The cost of protein (PD) and lipid deposition
with which body reserves are used for ATP           (LD) has been estimated experimentally by a
synthesis is not considered. Maintenance            factorial approach:
energy requirements are often expressed as a               ME = MEm + 1/ kp PD + 1/kf LD
metabolizable energy (ME) equivalent, which         where MEm is the maintenance energy
has the drawback that the value is not inde-        requirement, kp is the marginal efficiency of
pendent of the diet. A zero energy balance          protein deposition and kf the marginal effi-
(i.e. either induced experimentally or by statis-
                                                    ciency of lipid deposition. Although it is
tical extrapolation) ensures that all metaboliz-
                                                    acknowledged that there is considerable varia-
able energy is used for maintenance functions.
                                                    tion in reported values for marginal efficien-
The maintenance energy requirement repre-
                                                    cies, kp is typically much lower than kf (60
sents an important fraction of the energy
intake, ranging from 25–30% of ME intake            and 80%, respectively, in growing pigs). Con-
for very productive animals (such as high-pro-      sequently, more energy is required to deposit
ducing dairy cows or rapidly growing pigs and       1 kJ of energy as protein than as lipid. The
poultry) to 100% of ME intake in mature non-        greater energy requirement for protein depo-
producing animals. For mature species, main-        sition is due to the ATP needed for peptide
tenance requirements are typically expressed        bond formation (augmented by protein
per kilogram of metabolic body weight (kg           turnover). It is important to realize that kp
BW0.75) and range from 290–330 for cattle           and kf reflect the conversion of metabolizable
to 400–440 kJ ME kg 1 BW0.75 day 1 for              energy to retained energy and are therefore
sows. Normal physical activity is also consid-      diet dependent.
178                                       Energy retention




Gestation and egg production                        experimental efficiency of using dietary
From an energetic point of view, gestation in       energy for milk production is 60–65% in
farm animals is a complex process. Apart            ruminants and 70% in sows. This difference is
from the development of the fetuses, mater-         partly due to differences in the nutrients used
nal tissues such as the uterus, placenta and        for milk fat synthesis (e.g. volatile fatty acids
udder grow and become metabolically more            obtained from fermentation vs. carbohy-
active during gestation. Moreover, the female       drates). In early lactation, the energy require-
may not have reached maturity or may be in          ment for milk production (and maintenance)
the process of restoring body reserves follow-      may exceed the intake capacity of the animal,
ing a previous lactation and so fetal growth        resulting in mobilization of body reserves. The
may be accompanied by growth of maternal            efficiency with which this occurs is relatively
tissues. The energy retention by the fetuses is     high (80–90%).                           (JvanM)
typically assumed to be proportional to the         See also: Energy systems
birth weight and number of young born. Fetal
growth (mainly protein) and growth of the pla-      Energy retention: see Energy balance
centa and maternal tissues are relatively minor
during the initial phase of gestation and are       Energy source           A feed included in diets
often described by exponential functions. Dur-      primarily for the energy it supplies (in contrast
ing gestation, a considerable fraction of the       to protein sources). The major sources of
                                                    energy in animal feeds are carbohydrates
energy expenditure is due to oxidative metab-
                                                    (such as starch in cereal grains and cellulose in
olism (i.e. ATP synthesis and utilization) by the
                                                    forages) and lipids (such as the oils in
uterus and placenta and this expenditure may
                                                    oilseeds).                                (JMW)
even exceed that of the fetus(es). The com-
plexity of gestation and methodological differ-
                                                    Energy systems             Energy systems have
ences result in widely different estimates of
                                                    been developed as a means of relating the sup-
energy requirements of gestation between
                                                    ply of dietary energy to the animal’s require-
species. It is less difficult to determine the
                                                    ment (see figure). The objective of an energy
energy requirement of reproduction in poul-
                                                    system is to attribute a value to a feed that can
try. Based on the energy value of egg con-
                                                    be compared with a requirement expressed
stituents, at least 7 kJ g 1 egg mass is            using the same units. Most current energy sys-
needed. The metabolizable energy require-           tems are based on (or variants of) digestible
ment for egg production is typically assumed        energy (DE), metabolizable energy (ME) or net
as being 8.7 kJ g 1. This requirement covers        energy (NE). It is important to realize that, in
the synthesis of egg energy as well as the          refining energy systems, energy values become
energy required for synthesis (e.g. formation       not so much a property of the feed alone but
of the egg shell).                                  more a function of both the diet and the ani-
                                                    mal’s productive processes.

Lactation
The energy retained in milk is a function of        Digestible energy (DE)
the protein, fat and lactose contents of the        The DE content of a diet corresponds to the
milk. The heat of combustion of these prod-         gross energy (GE) content minus the energy
ucts is approximately 38.9, 23.9 and 16.5 kJ        lost in the faeces. The faecal energy corre-
g 1, respectively. In ruminants, lactose can be     sponds to the energy of undigested dietary
synthesized from gluconeogenic precursors           nutrients as well as a (small) endogenous frac-
such as propionate, whereas non-ruminants           tion. DE values cannot easily be determined
may use dietary glucose. The actual energy          in poultry, because the urine is excreted with
requirement for milk synthesis appears to be        the faeces. DE values may be extremely vari-
considerably greater than that calculated theo-     able and may range from 0 to 100% of the
retically from transforming nutrients to milk       gross energy value. The (apparent) DE value
components, especially in ruminants. The            may often be calculated from digestible nutri-
                                            Energy systems                                        179




                                      Gross                   Faecal energy
                                      energy




                                    Digestible                Urinary energy + CH4
                                     energy




                                   Metabolizable              Heat increment
                                      energy




                                       Net
                                      energy




                     Retained                      Net energy for               Heat
                      energy                       maintenance

Relation between energy systems.


ents. For example, the DE value of feeds (for         Metabolizable energy (ME)
growing pigs) has been determined by regres-          The ME value of a feed corresponds to the
sion as:                                              DE value minus the energy lost in the urine
       DE = 0.0229        DCP + 0.0389                and as gas. All ME is retained in animal prod-
    DEE + 0.0115 DCF + 0.0175 ST                      ucts or lost as heat. The energy losses in the
    + 0.0169 Sugars + 0.0183 DRes                     urine, mainly as urea in mammals or as uric
                                                      acid in birds, are principally due to the incom-
where DCP is the digestible crude protein
                                                      plete oxidation of amino acids. Urinary
content, DEE the digestible ether extract,            energy represents 2–5% of GE for non-rumi-
DCF the digestible crude fibre content, ST             nant animals and 4–6% for ruminants. Urea
the starch content, Sugars the sugar content          has an energy value of 22.6 kJ g 1 N (34.4
and DRes the digestible residue content (i.e.         kJ g 1 N for uric acid). Thus, each additional
organic matter minus the other digestible             gram of protein that is not deposited as pro-
nutrients), all expressed in g kg 1 dry matter        tein will theoretically result in an additional
(DM). It should be noted that the coefficients         urinary energy loss of 0.16       22.6 = 3.6 kJ
correspond to the (approximate) GE values             g 1 protein. Thus, the ME value of dietary
for each nutrient. Several equations of this          proteins that are deposited as protein will
type have been proposed and are all built on          equal the DE value (23.8 kJ g 1), whereas
the premise that digestible energy is supplied        that of oxidized amino acids will be 23.8 –
by the components of organic matter. It               3.6 = 20.2 kJ g 1. Consequently, the ME
must be ensured that DE values are repre-             value of protein is not a property of the pro-
sentative of the situation to which they are          tein content per se, but depends on the uti-
applied, as the digestibility of a nutrient may       lization of the protein. This has led to the
be affected by feeding level or physiological         suggestion that ME should be corrected to
stage of the animal. Although DE values of            zero balance or constant N retention. As with
feedstuffs can be easily determined, the bio-         DE, ME also contains an endogenous compo-
logical basis for establishing DE requirements        nent that is not (directly) of dietary origin.
is rather weak.                                       Also the gaseous energy (methane and hydro-
180                                           Energy units




gen originating from microbial fermentation)          cal value, suggesting that other processes (e.g.
cannot be used by the animal. Although this is        protein turnover) contribute to the effi-
a minor fraction for non-ruminants (0–2% of           ciency. The observation that the efficiency of
GE), it may represent 6–10% of the GE in              using protein for protein deposition is very
ruminants. The measurement of methane and             similar (0.60, which is essentially an ATP cost)
hydrogen production requires specialized              supports this idea. The result is that, relative to
equipment. Consequently, ME values are                an ME classification, feedstuff rich in protein
often calculated as a function of DE, digestible      and fibre have a low NE value (in pigs),
nutrients and/or organic matter digestibility.        whereas those rich in fat have a higher value.
                                                      The advantage of using an NE system (relative
                                                      to ME or DE) is that it corresponds more
Net energy (NE)
                                                      closely to the actual energy utilization by the
Net energy can be defined as the ‘useful’
                                                      animal. On the other hand, it results in differ-
energy for the animal and is equivalent to the
                                                      ent NE values for each type of production and
ME value minus the heat increment of
                                                      therefore becomes less of a diet characteristic
feeding. The latter is the heat loss associated
                                                      per se.                                   (JvanM)
with ingestion, digestion and metabolism of
nutrients and can be obtained by regression of
                                                      Energy units            The Standard Interna-
the energy balance (or heat production) on
                                                      tional (SI) unit of energy is the joule (J), which
the ME intake. The slope of this line is the effi-
                                                      is the work done when a force of 1 newton
ciency of production (kg = EB/ ME) and the
                                                      acts over a distance of 1 m. The calorie,
NE value can then be calculated as kg          ME
                                                      another unit of energy, is the heat required to
(the heat increment is (1 – kg) ME). The rela-
                                                      raise the temperature of 1 g of water through
tion between the energy balance and ME
                                                      1°C. The relationship 4.184 J cal 1 is known
intake is not necessarily linear and NE values
                                                      as the mechanical equivalent of heat.
are therefore not constant. The NE value of a
                                                          Use of SI units is recommended whenever
diet can also be seen as the sum of the NE val-
                                                      possible but calories (cal), kilocalories (kcal)
ues for maintenance and production. The NE
                                                      and pounds (lb) are widely used in agriculture.
for production corresponds to the energy that
                                                      The SI unit of time is the second (s) and the
is stored in animal products (e.g. growth, milk,
                                                      SI unit of power is the watt (1 W = 1 J s 1).
eggs) whereas the fasting heat production is
                                                      In agricultural practice, one is dealing with
typically taken as an estimate for the NE for
                                                      rates of heat output and food energy intake in
maintenance. Although the energy retained in
                                                      the range 1 W to 10 kW, but food intake and
milk and eggs can easily be measured, mea-
                                                      requirements are usually reckoned per 24 h.
surement of the energy balance requires the
                                                      This inevitably leads to the use of hybrid units
comparative          slaughter technique or
                                                      such as kilojoules per hour, megajoules per
calorimetry. Both techniques are costly and
                                                      day, kilowatt-hours, kilojoules per pound, etc.,
time consuming, which limits extensive mea-
                                                      as well as joules and calories. Some useful
surement on feeds. For most species, NE val-
                                                      conversion factors are as follows.
ues have been measured experimentally and
this information has been exploited to predict        Units of energy, including work and heat
the NE value from the chemical composition            (mass distance2 time 2):
or ME value of the feed. These (statistical) rela-        1 joule (J) = 1 watt second (W s) = 0.239
tions explain a large fraction of the biochemi-            calories (cal)
cal efficiency of nutrient transformation. In              1 kilojoule (kJ) = 0.278 watt hours (W h) =
growing pigs, the NE/ME ratio (for mainte-                 0.239 kilocalories (kcal)
nance and growth) for protein, ether extract,             1 megajoule (MJ) = 0.278 kilowatt hours
starch and dietary fibre correspond to approxi-             (kW h)
mately 0.58, 0.90, 0.82 and 0.58, respec-                 1 calorie = 4.184 joules (J)
tively. The value for starch is similar, whereas          1 kilocalorie (kcal) = 4.184 kilojoules (kJ) =
that for lipid is slightly lower than the theoreti-        1.162 watt hours (W h)
cal efficiency for lipid deposition. The value for     Units of power or work-rate (mass
protein is considerably lower than the theoreti-      distance2 time 3):
                                           Energy utilization                                     181




    1 watt (W) = 1 joule/second (J s 1) = 3.6         Energy utilization The metabolizable
     kJ/hour (kJ h 1) = 86.4 kJ day 1 =               energy (ME) cost of forming an animal prod-
     0.239 cal s 1                                    uct (e.g. milk, eggs, body tissue) is the extra
    1 kilowatt (kW) = 1 kJ s 1 = 3.6 MJ h 1 =         ME intake required for the formation of the
     86.4 MJ day 1 = 0.239 kcal s 1                   product over and above the ME required for
    1 joule/second (J s 1) = 1 W = 0.239 cal          the animal’s maintenance (MEm). The gross
     s 1                                              energy of the product is its heat of combus-
    1 kilojoule/hour (kJ h 1) = 0.278 W               tion. For cow’s milk this is approximately 3 kJ
    1 megajoule/day (MJ day 1) = 11.6 W               g 1, for sow’s and ewe’s milk 5 kJ g 1 and
    1 calorie/second (cal s 1) = 4.184 J s 1          for hen’s eggs 6 kJ g 1. For growth in most
    1 kilocalorie/hour (kcal h 1) = 1.162 W           species the gross energy of weight gains is of
Units of energy/mass (distance2         time 2,       the order of 6–10 kJ g 1 after birth when the
                                                      gain is mainly protein, rising to 25–30 kJ g 1
used for energy value of foods, heats of com-
                                                      at maturity when the gain is mostly fat.
bustion, energy expended in doing mechani-
                                                          The efficiency of energy utilization is the
cal work):
                                                      ratio between energy output (in product) and
    1 joule/gram (J g 1) = 0.239 cal g 1
                                                      the corresponding energy input. It can be
    1 kilojoule/kilogram (kJ kg 1) = 0.239
                                                      obtained from the relationship between
     kcal kg 1 = 0.454 kJ lb 1 = 0.1084 kcal
                                                      energy balance and metabolizable energy
     lb 1
                                                      intake (see figure). The slope of this line is
    1 megajoule/kilogram (MJ kg 1) = 108.4            interpreted as the efficiency of energy utiliza-
     kcal lb 1                                        tion (k). The relationship is usually repre-
    1 kilojoule/pound (kJ lb 1) = 0.239 kcal          sented as having two linear segments and can
     lb 1 = 2.205 kJ kg 1 = 0.527 kcal kg 1           be expressed by the equation
    1 calorie/gram (cal g 1) = 4.184 J g 1                    ME = Gross energy of product/k +
    1 kilocalorie/kilogram (kcal kg 1) = 4.184                             FHP/kM
     kJ kg 1 = 0.454 kg lb 1 = 1.90 kJ lb 1               At ME intakes above maintenance, k is the
    1 kilocalorie/pound (kcal lb 1) = 4.184 kJ        efficiency of utilization of ME for formation of
     lb 1 = 2.205 kcal kg 1 = 9.224 kJ kg 1           product (kL for lactation, kF for fattening,
                                       (JAMcL)        etc.). Below maintenance, the slope of the
See also: Calorific factors; International units       line between fasting heat production (FHP)




                                                                kproduction
      Energy balance




                                    MEm                             Metabolizable energy intake



                             km


                       FHP



Relation between the energy balance and metabolizable energy intake.
182                                          Energy utilization




and the metabolizable energy intake for main-              ATP synthesis as a fraction of energy input
tenance (MEm) indicates the efficiency with                 ‘retained’ as ATP. Nevertheless, the (relative)
which dietary nutrients are used for mainte-               efficiency with which nutrients can be used for
nance, relative to mobilizing body reserves for            ATP synthesis can be compared (see table). It
that purpose. This efficiency for maintenance               appears that glucose and lipids can be used
(km) depends on both the diet and the body                 relatively efficiently for ATP synthesis, whereas
reserves used when the animal is actually fed              volatile fatty acids are used 10–18% less effi-
below maintenance. With increasing ME                      ciently. The efficiency of using amino acids for
intake above maintenance, growing animals                  ATP synthesis is considerably lower. Part of
deposit an increasing fraction of energy as                this inefficiency is due to the incomplete oxida-
lipid (relative to protein). As the energetic effi-         tion of amino acids. In mammals, the nitrogen
ciencies of protein and lipid deposition differ,           of amino acids is excreted as urea, which
the linear relation is therefore overly simple.            involves both a physical loss of energy (as
    The efficiency of utilization of ME is gener-           urea) as well as the energy expenditure to syn-
ally higher for higher quality (i.e. higher                thesize it (2 ATP/N).
metabolizability) foods. For maintenance, km                   The theoretical energetic efficiency of pro-
is usually of the order of 0.65–0.85, for lacta-           tein synthesis is approximately 85% but the
tion kL = 0.55–0.65, for growth kG =                       actual efficiency is often lower due to protein
0.35–0.55 and for milk-fed growing animals                 turnover. The efficiency of depositing protein
up to 0.7. For egg production kE = 0.7. The                in animal tissue appears to be considerably
ME cost of an entire pregnancy is approxi-                 lower (~60%) than that of depositing protein
mately 7.5 J per J gross energy of a newborn               in animal products such as milk or eggs
calf, i.e. an efficiency of 0.13. If food intake is         (~75%). Part of this difference may be due to
insufficient for essential needs such as fetal or           a difference in protein turnover between
skeletal growth or milk production these func-             these types of production.
tions still proceed, albeit at reduced rates,                  In ruminants, a major part of the energy
obtaining their energy from catabolism of                  supply is derived from the end-products of
body reserves (mainly fat). The (relative) effi-            fermentation. The metabolic utilization of
ciency for this is usually of the order of 0.9.            these end-products (and the associated cost
    Because km is a relative efficiency, its value          of fermentation) results in lower efficiency
typically exceeds that of the efficiency of pro-            than that observed in non-ruminant animals.
duction and even may exceed unity. The main-               As with the efficiency for ATP synthesis, the
tenance energy requirement is essentially a                efficiency for fat deposition in non-rumi-
requirement for adenosine triphosphate                     nants increases in the order protein, carbo-
(ATP). It is difficult to express the efficiency of          hydrate, lipid.                 (JAMcL, JvanM)


                The theoretical energy expenditure for ATP synthesis from various substrates.

                Source                  kJ mol   1   ATP       Source          kJ mol   1   ATP

                Glucose                     74.0            Phenylalanine         124.0
                Tri-stearin                 75.7            Tyrosine              107.0
                Acetate                     87.4            Histidine             149.8
                Propionate                  85.4            Arginine              133.6
                Butyrate                    81.2            Serine                116.0
                Lysine                     102.2            Glycine               149.2
                Methionine                 129.3            Alanine               104.5
                Cysteine                   178.4            Glutamate              91.8
                Threonine                  100.0            Proline                92.5
                Tryptophan                 134.0            Aspartate             103.9
                Isoleucine                  88.4
                Leucine                     90.6
                Valine                      92.7
                                   Environment–nutrition interation                              183




Further reading                                      Enterokinase          A proteolytic enzyme
Agricultural Research Council (1980) The Nutrient    (enteropeptidase: EC 3.4.21.9), secreted by
   Requirements of Ruminant Livestock. Com-          epithelial cells of the duodenum, that specifi-
   monwealth Agricultural Bureaux, Farnham           cally activates trypsin by the cleavage of a
   Royal, UK.
                                                     lysine–isoleucine peptide bond leading to the
Agricultural Research Council (1981) The Nutrient
                                                     removal of an aspartyl-rich octapeptide from
   Requirements of Pigs. Commonwealth Agricul-
   tural Bureaux, Farnham Royal, UK.
                                                     the NH2-terminal of the inactive zymogen,
Janssen, W.M.M., Terpstra, K., Beeking, F.F.E. and   trypsinogen.                              (SB)
   Bisalsky, A.J.N. (1979) Feeding Values for        See also: Protein digestion
   Poultry. Spelderholt Institute for Poultry
   Research, The Netherlands.                        Environment–nutrition              interaction
                                                     Climate is not the only component of the
Energy value           The concentration of          environment that affects nutrition (lighting
energy in a feed, usually expressed as mega-         and social environment are also important)
joules (MJ) per kg dry matter (DM).    (JMW)         but it is the one that receives most attention.
See also: Digestible energy; Gross energy;           The underlying cause of climate–nutrition
Metabolizable energy; Net energy                     interactions is that mammals and birds are
                                                     homeothermic (or endothermic), which
Englyst method           An in vitro procedure       means that they maintain a near-constant
for the determination of resistant starch. The       body temperature. This can occur only if heat
sample is treated with a combination of mam-         production equals heat loss. Over a range of
malian and bacterial amylolytic enzymes under        ambient temperature, known as the ther-
controlled conditions for various periods of         moneutral zone, or zone of minimal ther-
time to give estimates of rapidly digestible         moregulatory       effort,   constant      body
starch (RDS), slowly digestible starch (SDS)         temperature is maintained by physical means,
and total starch (TS). Resistant starch is calcu-    with no change in metabolic rate. This zone
lated as TS (RDS SDS).                     (MFF)     is narrow in poultry, intermediate in pigs and
                                                     relatively broad in ruminants. Below the ther-
Enrichment (isotopic)           The concentra-       moneutral zone, energy intake usually
tion of a particular isotope in a sample of the      increases as ambient temperature decreases.
element. Because each isotope has a certain          Above the thermoneutral zone, energy intake
natural abundance, enrichments are usually           decreases. The rate of decrease above ther-
referred to as that value and expressed as           moneutrality usually shows two phases. Ini-
‘atoms percent excess’ (ape). For example,           tially, intake decreases at a rate that reflects
the natural abundance of 15N, i.e. the propor-       the decrease in metabolic rate and the conse-
tion of all nitrogen on earth that is of mass        quent decrease in maintenance energy
15, is about 0.36%. So a sample with an              requirement. As temperature increases still
enrichment of 2.48% has ape 2.12.        (MFF)       further, there is often an increased rate of
                                                     decline in energy intake, which may be a
Ensiling: see Silage                                 mechanism for reducing the heat increment
                                                     of feeding. There is usually a further accelera-
Enterocyte         A cell of the single layer of     tion in the decline of food intake with the
columnar cells on the surface of the villi of the    onset of hyperthermia. Farmed fish are poik-
small intestine. Enterocytes are in direct con-      ilothermic (or ectothermic) and their body
tact with the intestinal contents. They have a       temperature is close to that of the surround-
directional orientation toward the intestinal        ing water. Their metabolic rate and nutrient
lumen. On their luminal surface are the              requirements therefore increase with ambient
microvilli (brush border) which dramatically         temperature, following the Q10 relationship
expand the contact surface and contain some          (i.e. a temperature increase of 10°C caused a
of the digestive enzymes (e.g. lactase and           two- to threefold increase in rate from the ini-
sucrase) and transporters.                 (NJB)     tial level).
184                                                 Environmental temperature




    Intake of dietary energy is the nutritional                       Breeds indigenous to hot climates are gen-
variant most directly affected by ambient tem-                    erally better able to maintain their characteris-
perature. To maintain the required intakes of                     tic level of production at temperatures that
essential nutrients it may therefore be necessary                 severely limit the performance of imported
to alter the ratio of nutrients to energy as tem-                 ‘modern’ genotypes. However, their greater
perature varies. This may be most practicable in                  tolerance can be seen as a consequence of
the case of housed pigs and poultry, where                        the lower metabolic intensity accompanying
there is good control of the composition of the                   their lower rate of production.        (MMacL)
diet. The most widely applied dietary alteration                  See also: Environmental temperature; Heat
is to increase the ratio of essential amino acids                 increment of feeding; Hyperthermia; Temper-
to energy as temperature increases. This has                      ature, body; Thermoregulation
some beneficial effect in allowing growth rates
                                                                  Environmental          temperature         The
to be sustained at high ambient temperature.                      effects of environmental temperature on heat
However, it is not always successful in prevent-                  exchanges of animals are illustrated in the fig-
ing a reduction in growth rate or production.                     ure, which is a model generally applicable to
There are clearly direct (physiological) effects of               all homeothermic (warm-blooded) animals.
high temperature that cannot be prevented by                      Homeotherms maintain their deep-body tem-
dietary adjustment. It has sometimes been sug-                    perature (TB, usually measured as rectal tem-
gested that providing more energy in the form                     perature) close to a fixed normal level of
of fat rather than carbohydrate should be bene-                   around 38°C. TB varies between species and
ficial at high temperatures because of its lower                   tends to be higher (up to 40°C) in small ani-
heat increment, but this has not invariably been                  mals than in large ones.
borne out in practice.                                                Except in cold and extremely hot condi-
    Increased dietary vitamin supplementation                     tions, the rate of heat production is not
(especially with vitamins E and C) has been                       affected by the environment but is determined
shown to alleviate some of the effects of heat                    largely by the levels of food intake and activ-
stress. This is most likely to be due to their                    ity; it is shown in the model as a horizontal
antioxidative effects, particularly in protecting                 straight line between the two environmental
the cell membranes of metabolically active tis-                   temperatures TC and Tmax. TC is known as the
sues such as the liver.                                           critical temperature.




                              Chemical regulation                      Physical regulation
                          He
                               at                   Comfort
                                    pro
                                       dn
                          No
      Heat exchanges




                               n-e
                                    vap
                                          . lo
                                              ss




                          Evap. loss


                                                    Environmental temperature
                       Tmin                         TC                            TB                  Tmax


Effect of environmental temperature on heat exchange.
                                       Environmental temperature                                   185




    The heat exchange between an inanimate            ture), heat production is increased by increased
object and its surroundings is proportional to        voluntary activity or by shivering as the temper-
the temperature difference between them               ature falls. Above TC, in the first part of the
(Newton’s law of cooling). It is obviously an         physical zone, reflex changes in blood flow just
over-simplification to apply this law to an ani-       below the skin surface alter the thermal insula-
mal – which is clearly not inanimate and has          tion of the tissues, causing the transition
the ability to alter its rate of heat loss by vari-   between the lines of minimal and maximal non-
ous means, both reflex and behavioural, as             evaporative heat loss. This is the comfort zone.
well as to lose heat by evaporation – but for         As the temperature increases further (still
simple consideration of non-evaporative heat          within the physical zone), increased evapora-
exchanges (i.e. convection, conduction and            tion is caused by sweating or panting. The term
infrared radiation to the immediate surround-         ‘thermoneutrality’ is used by some authors to
ings) an animal may be thought of as two sep-         refer to the entire physical zone and by others
arate inanimate objects: one with minimal             just to the comfort zone; the ‘zone of least ther-
insulation for warm environments and the              moregulatory effort’ has also been suggested to
other with maximal insulation for cold ones.          replace ‘comfort zone’ (Mount, 1974).
These are represented in the model as two                 Among many deficiencies of this model is
straight lines of different slopes (insulation),      the fact that heat balance is only imperfectly
both passing through or extrapolating to the          achieved. TB alters slightly and the tempera-
point of zero heat exchange at the environ-           tures of the limbs and of peripheral regions of
mental temperature that corresponds to TB.            the trunk alter considerably more. Periods of
The transition between these two lines is             imbalance between heat production and heat
shown in the model as occurring over a short          loss give rise to temporary storage of heat in
range of environmental temperature above TC.          the body. The simple model also fails to take
    Since TB remains near to a fixed level, it         account of solar radiation. Solar heat load can
follows that heat balance is only maintained if       be very considerable – even higher than the
evaporative heat loss is regulated at a level         normal level of resting heat production. It can
equal to the difference between heat produc-          be included in the model by regarding it as an
tion (which is constant) and non-evaporative          addition to heat production. To maintain heat
heat loss. Evaporative heat loss thus decreases       balance, evaporative heat loss must be
from a high level at Tmax to near zero at TC,         increased by a similar amount. These altered
and it is represented in the model by a               levels, consequent on solar radiation, are
straight line whose slope is equal but opposite       shown by dashed lines on the model. The net
to that of non-evaporative loss.                      effect is a lowering of TC and of temperatures
    At environmental temperatures below TC,           in the comfort zone. Wind accelerates heat
evaporative loss is at a fixed minimal level           exchanges by reducing thermal insulation.
consistent with minimal respiratory activity; it      The effect on the model is to make the slope
appears on the model as a horizontal line             of all lines steeper.
slightly above zero heat loss. In this cold               In addition to the reflex actions described
region, heat balance is achieved by increasing        above, animals (when free to do so) adopt
heat production; it is shown as a straight line       behavioural patterns that influence heat
following the increased non-evaporative heat          exchanges. These include sheltering, huddling
loss as the temperature falls. A limit occurs         and curling up so as to limit heat losses in
when the animal attains its so-called summit          cold weather and standing in the wind or
metabolism and is unable to increase heat             seeking shade when the weather is warm.
production any further (at Tmin).                         For small animals the comfort zone is very
    Between Tmin and Tmax, which represent            narrow, perhaps better described as a comfort
limiting environmental conditions for survival,       point; for large farm animals it is only a few
lie the zones of chemical and physical body-          degrees wide. The table gives approximate crit-
temperature regulation. In the chemical zone,         ical temperatures (°C) for some farm animals
starting at the critical temperature (TC, some-       exposed to neither solar radiation nor wind.
times also known as the lower critical tempera-                                                (JAMcL)
186                                              Enzootic ataxia




       Critical temperatures (°C) for sheltered animals.

                                                                             Mature

       Species                       Newborn               Maintenance fed            Lactating/laying

       Cattle                           14                          7                       –30
       Sheep                            29                         –3                        40
       Pigs                             32                         23                        14
       Chickens                         35                         16                        20



See also: Climate                                          Enzymes as feed additives               Enzymes
                                                           are proteins that act as biological catalysts.
                                                           They are produced by living cells and are inti-
Key reference
Mount, L.E. (1974) The concept of thermal neutral-
                                                           mately involved in essential transformations of
  ity. In: Monteith, J.L. and Mount, L.E. (eds)            substrates into products in biological systems.
  Heat Loss from Animals and Man. Butter-                  Many require non-protein co-factors. Enzyme
  worths, London, pp. 425–439.                             activity depends on the co-factors present, the
                                                           concentration and nature of substrate and
Enzootic ataxia        A gait disorder seen in             enzyme as well as temperature and pH. The
young lambs, goat kids and deer, in Australasia            function of enzymes is critically dependent on
and North America. It has also been seen in                their structure and they are therefore very sus-
pigs. Swayback is a similar condition seen in              ceptible to pH and temperature changes.
lambs and goat kids in the UK: some breeds of                  Enzymes are systematically named and
sheep are much more susceptible than others.               each has an Enzyme Commission (EC) num-
Both conditions are caused by copper defi-                  ber which describes the reaction that it cataly-
ciency and are associated with demyelination               ses. The source of the enzyme (e.g.
of the cerebrum or spinal cord.        (WRW)               Aspergillus niger) is also frequently cited.
See also: Copper                                           Enzymes are often referred to as carbohy-
                                                           drases, proteases, lipases, phytases, etc., indi-
Enzyme          A protein (or sometimes more               cating that their major function is the
than one protein) that has the ability to catal-           degradation of carbohydrates, proteins, lipids
yse a specific chemical reaction. Enzyme                    and phytic acid esters, respectively.
activity requires specific conditions of temper-                Enzymes are produced commercially from
ature, pH, substrate and co-factor concentra-              microbes, fungi and yeasts in highly controlled
tions, etc. Since enzymes act as catalysts they            conditions in fermentation plants. Their main
are not consumed while carrying out reac-                  uses are in the detergent and food industries
tions. Enzyme activity can be reduced by                   but significant quantities are manufactured for
enzyme inhibitors.                        (NJB)            use in animal diets. As feed additives, enzymes
                                                           are mainly used in the diets of non-ruminants
Enzyme activity          The potential of an               but are also added to ruminant diets. Their
enzyme, which may be one protein or a                      main purpose is to improve the nutritive value
group of proteins, to carry out a reaction                 of diets, especially when poor-quality, and usu-
under idealized conditions. It can be measured             ally less expensive, ingredients are incorpo-
using a purified protein or a sample of                     rated. It has been estimated that about 95% of
homogenized cells, tissue or organ. The sys-               intensively fed poultry are now given diets con-
tem is optimized for pH, temperature, co-fac-              taining supplementary enzymes. In some cir-
tor(s) and substrate concentration(s) and the              cumstances enzyme supplementation can
reaction is assessed over a measured time.                 improve performance and nutrient utilization
Results are expressed as a rate in relation to             by as much as 20%. The efficacy of a feed
the amount of sample, e.g. mol (min        mg              enzyme depends on the nature and quantity of
protein) 1.                              (NJB)             its substrate in the diet, the specific ingredi-
                                         Enzymes as feed additives                                           187




ents, the age of the animal and its nutritional               In poultry, the residence time of digesta in
and disease status. Enzyme supplementation                the gastrointestinal tract is relatively short
has the greatest effect on the young animal.              (4–6 h); it is longer in the pig (6–8 h) and
    The feeds of plant origin used in poultry             longer still in ruminants. Thus exogenous
and pig diets are often by-products of human              enzymes have greater opportunity to function
food and of poor quality, with high concentra-            effectively in ruminants and pigs than they do
tions of non-starch polysaccharides (NSPs)                in poultry; however, this also depends on pH,
and oligosaccharides, as well as proteins that            buffering capacity and other conditions in the
are resistant to digestion, and antinutrients             gastrointestinal tract. Generally, the enzymes
such as tannins, trypsin inhibitors, lectins and          required for ruminants are different from
phytates. Such feeds cause physico-chemical               those needed in diets for pigs and poultry. For
problems – increased digesta viscosity, water             ruminants, cellulases and hemicellulases are of
intake and moisture in the gut – that lead to             particular interest, whereas the NSPs and
reduced nutrient availability and increased               phytases are especially useful in diets for non-
endogenous losses. Nutrients are frequently               ruminants.
enclosed in cells with indigestible cell walls,               Enzymes can be added to diets as powders,
making them inaccessible to the animal’s own              granules or liquids. The solid material is added
digestive enzymes. Supplementation with the
                                                          during mixing while the liquid can be applied
correct enzymes can increase the availability
                                                          to pellets. The thermal stability of exogenous
of nutrients and alleviate the adverse effects of
                                                          enzymes is extremely important in diets that
antinutrients. In some instances, however,
                                                          are heated, either to reduce transfer of patho-
enzymes may actually release antinutrients.
                                                          genic microorganisms or when the diets are
    Enzymes used as feed supplements are car-
                                                          pelleted. Overheating can denature supple-
bohydrases, proteases, phytases and, to a
lesser extent, lipases. They may be used singly           mental enzymes, reducing their potencies.
or in combination. The carbohydrases can be                   A benefit of supplemental enzymes in diets
subdivided according to their substrate,                  for non-ruminants has been in reducing the
whether starch or NSPs such as -glucans,                  occurrence of wet, sticky faeces. This tends to
cellulose, hemicellulose, xylans, galacturonans           reduce the incidence of dirty animals, prod-
and galactans. For use in the European                    ucts and litter; it also tends to decrease conta-
Union, the enzyme preparations must be reg-               mination of the animals with dangerous
istered with the EU Scientific Committee on                bacteria such as Clostridium spp. Supple-
Animal Nutrition. The table gives a summary               mental enzymes frequently reduce the viscos-
of the enzymes available and their sources.               ity of digesta in the gastrointestinal tract. (TA)



Enzymes and the organisms from which they are obtained.

Enzyme                                                    Main sources

Phytases
 3-phytase (EC 3.1.3.8)                                   Aspergillus spp., Trichoderma spp.
 Phosphoric monoester hydrolase (EC 3.1.3.26)             Aspergillus spp.
Carbohydrases
 Endo 1→3 (4)- glucanase (EC 3.2.1.6)                     Trichoderma spp., Aspergillus spp., Geosmithia spp.,
                                                          Penicillium spp., Humicola spp., Bacillus spp.
 Endo 1→4- xylanase (EC 3.2.1.8)                          Trichoderma spp., Aspergillus spp., Geosmithia spp.,
                                                          Penicillium spp., Humicola spp., Bacillus spp.
 Alpha galactosidase (EC 3.2.1.22)                        Aspergillus spp.
 Polygalacturonase (EC 3.2.1.15)                          Trichoderma spp., Aspergillus spp.
 Alpha amylase (EC 3.2.1.1)                               Bacillus spp., Humicola spp., Trichoderma spp.
Proteases
 Subtilisin (EC 3.4.21.62)                                Bacillus spp.
 Bacyllolysin (EC 3.4.21.62)                              Bacillus spp.
188                                       Enzyme inhibitors




Further reading                                      growth plate, but growing separately from the
Acamovic, T. (2001) Commercial application of        shaft and covered by a layer of articular carti-
   enzyme technology for poultry production.         lage.                                  (MMax)
   World’s Poultry Science Journal 57,
   225–242.
                                                     Ergocalciferol          A trivial name for vita-
Bedford, M.R. and Partridge, G.G. (eds) (2000)
   Enzymes in Farm Animal Nutrition. CAB
                                                     min D2 or a specific vitamin D compound that
   International, Wallingford, UK.                   possesses the ergosterol side-chain. It is one
European Union (2001) Report of the Scientific        of the two common nutritional forms of vita-
   Committee for Animal Nutrition on the Use of      min D, the other form being cholecalciferol or
   Certain Enzymes in Animal Feedingstuffs. Web      vitamin D3. Unlike vitamin D3, this compound
   address, March 2001, http://europa.eu.int/        is not formed in the body but is produced by
   comm/food/fs/sc/scan/out52_en.pdf                 ultraviolet irradiation of ergosterol. The struc-
                                                     ture of ergocalciferol is:
Enzyme inhibitors             A term applied to
both inorganic and organic substances that
have a negative effect on enzyme activity.
Inhibitors    compete      with    the    normal
substrate(s) or co-factor(s) for the enzyme and
decrease the rate of reaction. The effective-
ness of the inhibitor is described in many
cases by the amount of the inhibitor required
to suppress the activity of the enzyme by
50%. This is referred to as the Ki and has
                                                         It can only be used in mammals. It has low
units such as nmol l 1. The smaller the value
                                                     biological activity in birds because it is rapidly
for the Ki, the more powerful is the inhibitor.
                                                     metabolized. In mammals its activity is equal
Important examples of the role of enzyme
                                                     to that of vitamin D3 or cholecalciferol.
inhibitors in nutrition are the trypsin inhibitors
found in many foods, especially legume seeds.                                                 (HFDeL)
                                            (NJB)
                                                     Ergosterol       A sterol found in plants,
See also: Feedback inhibition
                                                     yeast and moulds having the structure:
Epinephrine          A catecholamine, also
called adrenaline, produced in the adrenal
medulla from the amino acid L-tyrosine. Epi-
nephrine is released in response to both phys-
ical and physiological challenges. It causes the
liver and muscle to increase the rate of glyco-
gen breakdown, increases the release of fatty
acids from adipose tissue and increases circu-           Upon irradiation with sunlight or ultraviolet
lating lactate. An increase in metabolic rate is     light it is converted to ergocalciferol or vita-
often noted in response to epinephrine.              min D2, having the structure:
      O

                                      N

          O
                             O

                                            (NJB)

Epiphyses        Separate, enlarged, terminal
ossifications of long bones attached to a                                                     (HFDeL)
                                          Escherichia coli                                      189




Ergot         Ergot alkaloids are produced by       fed at more than 5% of diet, resulting in
Claviceps fungi infecting grains and grass          slower mitochondrial oxidation of substrates.
seeds, and by Neotyphodium coenophialum                 Erucic acid is found in large amounts in
endophytic fungi infecting grasses such as tall     some rapeseed oils, mustard seed oil and also
fescue (Festuca arundinacea). Claviceps pur-        crambe, meadow foam, nasturtium and
purea, C. paspali and C. cinerea are the            lunaria seeds. The erucic acid content of rape-
three major fungal species. The fungus para-        seed oil is controlled by two genes and zero-
sitizes the grass, attacking the ovary and          erucic acid rapes are now available. The EU
replacing the developing seed with an               has set maximum levels for erucic acid in
enlarged, black structure in which fungal           human foodstuffs at 2%. Erucic acid and its
spores are contained in a resin that eventually     derivatives are used in industry, for example
hardens, forming the sclerotium or ergot            as lubricants.                             (EM)
body. The ergot body may be harvested with
the seed head or consumed by animals graz-          Escherichia coli              A Gram-negative
ing an infected pasture.                            bacterium which is a normal inhabitant of
    The fungus produces toxic ergot alkaloids,      the gut of most mammals and birds. It is
including ergonovine, ergotamine and ergov-         excreted in faeces and can survive in the
aline, which are derivatives of lysergic acid.
                                                    environment for many weeks or even
The hallucinogenic drug of abuse, lysergic
                                                    months. There are several different strains,
acid diethylamide (LSD), is an ergot alkaloid.
                                                    most of which are not pathogenic. They can
Symptoms of ergotism include hyperthermia
                                                    be distinguished and described by serotyping
(elevated body temperature), vasoconstriction
                                                    the O (cell wall), K (capsular), H (flagellar)
and gangrene of extremities (e.g. fescue foot)
                                                    and F (fimbral) antigens.
and behavioural effects such as hyperex-
                                                        Pathogenic E. coli can cause enteritis or
citability, convulsions and poor coordination.
                                                    septicaemia in young animals, oedema dis-
There are three main combinations of symp-
toms in livestock: the convulsive form, con-        ease in weaned pigs, mastitis, urogenital infec-
sisting of convulsions, laboured breathing,         tions or toxaemia, depending on the strain
lack of coordination, excessive salivation and      and on the species of host animal.
diarrhoea; the gangrenous form, producing               Pathogenicity may depend on the pres-
dry gangrene of the nose, ears, legs and tail;      ence of an antigen on the surface of the bac-
and the reproductive form, consisting of            terium which allows adhesion to the intestinal
abortion, agalactia and reduced neonatal sur-       wall or the ability to produce toxins. Toxins
vival. A major sign of tall fescue toxicity (sum-   either act locally in the gut or are absorbed
mer fescue toxicosis) is ergot alkaloid-induced     and target other cells. Many strains of E. coli
hyperthermia. Young poultry are also suscep-        are secondary or opportunist pathogens.
tible to ergotism, with the symptoms of             Those that are pathogenic for one host
severe toxicosis being poor feathering, ner-        species may not be for others; for example,
vousness, incoordination and gangrene of the        E. coli strain 0157, which has caused major
foot and beak. Prevention of ergotism is only       food-poisoning incidents in humans, is car-
possible by removing animals from infected          ried undetected in the gut of a small propor-
feed or removal of the ergots from the grain        tion of cattle and other species. There may
by screening.                        (DRG, PC)      be variations in susceptibility within species to
                                                    different genotypes, e.g. in piglets to E. coli
Erucic acid                       A long-chain      strain K88.
monounsaturated       fatty    acid   (C22 13,          Specific strains of E. coli can be controlled
CH3·(CH2)7·CH= CH·(CH2)11·COOH). Diets              by vaccination, either of the dam to provide
in which erucic acid forms a major part of          passive immunity, or directly of the suscepti-
dietary fatty acids are associated with fatty       ble animal. Vaccine–antisera combinations are
infiltration of the heart, with subsequent per-      available for enteric disease and there is also a
manent damage. Erucic acid has also been            vaccine to aid in the control of E. coli mastitis
associated with liver damage in rats when           in cattle.                                  (EM)
190                                     Essential amino acids




Essential amino acids             Those amino       1920s showed that fat or some component
acids that the animal under consideration can-      in the fat was required to support expected
not synthesize at a rate adequate to achieve        rates of growth and reproduction in labora-
optimal performance. To meet physiological          tory rats. Previously it was thought that fat
needs, these amino acids must be supplied in        could be made from carbohydrate or the car-
the diet or, in ruminants, by the rumen             bon skeletons from amino acids, thus fat
microflora. In contrast, non-essential amino         itself should not be an essential dietary ingre-
acids can be synthesized in adequate quanti-        dient. Later, polyunsaturated fatty acids
ties from simpler precursors, for example glu-      were shown to counteract the growth-
cose or pyruvate together with an amino             depressing effects of a fat-free diet. This was
group. The non-essential amino acids are            the first indication of a dietary requirement
none the less components of protein and are         for something that was classified as a fat. Of
therefore physiologically essential for body        the three polyunsaturated fatty acids usually
protein synthesis. The terms ‘indispensable’        thought of as EFAs – linoleate (18:2 n-6),
and ‘dispensable’ are often considered prefer-      linolenate (18:3 n-3) and arachidonate (20:4
able. The nine amino acids that are generally       n-6) – the highest biopotency for growth is
considered essential for all non-ruminant           seen with arachidonate. Arachidonic acid
mammalian and avian species are lysine, thre-       is found predominantly in animal tissues
onine, methionine, leucine, isoleucine, valine,     whereas linoleic acid is distributed in plant
phenylalanine, histidine and tryptophan. De         oils. Arachidonic acid itself cannot be classi-
novo biosynthesis of these amino acids is           fied as an essential fatty acid since it is
essentially zero. Arginine is partially synthe-     derived from linoleic acid in metabolism. The
sized in mammals, but not at a rate sufficient       classical symptoms of EFA deficiency are
for maximal growth. It is not synthesized at all    growth depression, decreased reproduction,
by avian species and for them it is therefore       decrease in skin integrity (more evaporative
an essential amino acid.                            loss), tissue membrane degradation, and
    For maximal growth of broiler chicks and        changes in fatty acid concentrations in blood
turkey poults, small quantities of glycine (or      and tissue lipids. Humans given a fat-free
serine) and proline must be present in the          diet intravenously had evidence of an EFA
diet. Biosynthesis of these amino acids occurs,     deficiency (altered triene:tetraene ratio) by
but the quantities synthesized fall short of the    14 days and in some cases by 2 days. Rumi-
total needs for these amino acids.                  nants seem to be unexpectedly resistant to
    Tyrosine and cysteine are called semi-          similar treatments. A number of hormones
essential amino acids, because tyrosine can be      are derived from the essential fatty acids.
synthesized in the body from phenylalanine          Each EFA is a precursor for a separate series
and cysteine can be synthesized from methio-        of     prostaglandins,    thromboxanes      and
nine and serine. Taurine, a non-protein amino       leukotrienes – hormones intimately involved
acid that is made from cysteine, is synthesized     in cell and tissue metabolism. A marker of
inefficiently by feline species and for them it is   EFA deficiency is the triene:tetraene ratio in
therefore considered an essential amino acid.       plasma, erythrocyte or tissue lipid. A ratio
                                          (DHB)     less than 0.4 suggests the diet meets the
                                                    EFA requirement. A decrease in the dietary
Essential fatty acids            Essential fatty    availability of linoleate (18:2 n-6) results in
acids (EFAs) are 18- to 20-carbon unsatu-           lower      concentrations    of   arachidonate
rated fatty acids having at least two double        (20:4 n-6) which normally suppresses the
bonds. The term ‘essential fatty acids’ means       conversion of oleate 18:1 n-9 to 20:3 n-9.
that they are essential for life and must be        This results in a triene:tetraene ratio above
provided in the diet to prevent death. These        0.4, which is representative of a deficiency.
fatty acids are dietary essentials because ani-     The minimum requirement for linoleate lies
mal systems do not have enzymes that can            between 1 and 2% of dietary calories for
insert a double bond distal to n-9 carbon in a      rats, pigs and infants.                   (NJB)
fatty acid. Experiments carried out in the late     See also: Eicosanoids
                                          Evaporative heat loss                                   191




Key reference                                         boiling point 123–125°C. A light yellow to
Holman, R. (1964) Nutritional and metabolic inter-    brown liquid with an unpleasant, mercaptan-
   relationships between fatty acids. Fed Proc. 23,   like smell. It is combustible (flash point 107°C)
   1062–1067.                                         and incompatible with oxidizing agents. It
                                                      polymerizes if heated.                      (MG)
Esterification        The formation of ester           See also: Antioxidant
bonds. For example, a carboxyl carbon
R·COO reacts with an alcohol R·COH to                 Ethylenediamine tetraacetic acid (EDTA)
produce an ester R·CO·OCH2·R. Examples                (HOOC·CH 2 ) 2 NCH 2 ·CH 2 N(CH 2 ·COOH) 2 .
are found in the triacylglycerol (triglyceride)       An excellent chelating ligand molecule which
molecule of a neutral fat when a fatty acid           is hexadentate. It forms strong complexes that
reacts with the alcohol group of glycerol or          wrap around metal cations, reducing their bio-
similar linkages in phospholipids. Another            logical activity. Chromium EDTA has been
example is cholesterol esters in which unsatu-        used as an indigestible fluid marker in
rated or saturated fatty acids react with the         digestibility studies (see Feed evaluation).
alcohol group OH of carbon 3 of cholesterol           EDTA may also be used to strip toxic metals
to form an ester bond.                   (NJB)        from the body and facilitate their excretion
                                                      (chelation therapy).                      (IM)
Ester        An organic compound in which
the replaceable hydrogen of an acid can be            EU regulations            Directives issued in
replaced by an alkyl radical. Esters can be           Brussels by the European Commission regu-
made on carboxyl carbons of fatty acids, phos-        late member states of the European Union on
phate (PO42–) in ATP, and sulphate (SO42–) in         many issues. In the case of animal feeds these
heparin. Esters occur in neutral fats the fatty       regulations include: target species; prohibition
acid binding to the alcohol group of glycerol         of feeds; feed processing requirements; feed
(·R·H2CO·OC·(CH2)14·CH3) and where a fatty            contamination, composition and labelling; the
acid binds to the alcohol group R·OH of cho-          marketing and management of animal food-
lesterol or -tocopherol. The phosphate esters         stuffs; and licensing of mineral supplements,
of ATP are R·O·P=O(OH)·O·R. The sulphate              pharmaceuticals and feed additives.       (JKM)
esters of heparin are glucosamine·O·SO3H.
                                         (NJB)        European sea bass (Dicentrarchus
                                                      labrax)           A eurythermal, euryhaline
Ethanol       A monohydric primary alcohol            species living in coastal and brackish waters of
(C2H5OH, molecular weight 46), most com-              the eastern Atlantic, ranging from Norway to
monly produced by the fermentation of carbo-          the Mediterranean and Senegal. It is grown in
hydrates such as molasses and cereal grains           brackish lagoons and sea cages. Sea bass is
by Saccharomyces yeast.               (JKM)           spawned in full sea water, the larvae being fed
                                                      initially on live prey organisms such as rotifers
Ether extract          The residue obtained           and artemia enriched with amino acids, vita-
when a feed sample, or other material, is con-        mins and n-3/n-6 polyunsaturated fatty acids,
tinuously extracted (4–16 h) with diethyl ether;      then switched to formulated micro-diets. A
in the proximate analysis of foods it is a mea-       market size of 300–400 g is attained in
sure of crude fat content. Water-soluble sub-         12–18 months at temperatures near 20°C.
stances may first be removed from the sample                                                     (RHP)
by extraction with several portions of water;
the sample is then dried and continuously             Evaluation, feed: see Feed evaluation
extracted, in a Soxhlet apparatus, with anhy-
drous diethyl ether. The extract is weighed           Evaporative heat loss          Evaporation is
after evaporation of the ether.           (CBC)       a powerful means of dissipating heat from the
                                                      animal’s body to the environment, especially
Ethoxyquin        An antioxidant, dihydro-6-          in warm climates. The heat required to con-
ethoxy-2,2,4-trimethylquinoline, C14H19NO,            vert liquid into vapour (the latent heat of
192                                            Ewe




vaporization of water) is approximately 2.2 kJ     mature weight at mating. Thereafter their
g 1; this heat is drawn from the evaporating       weight gains should be moderate (1–1.5 g
surface, which may be the skin, lungs or res-      kg 1 estimated mature weight day 1) rather
piratory passages. There is a minimal rate of      than excessive (three- to fourfold higher) as
evaporation due to normal respiration and dif-     the latter leads to excessive partitioning of
fusion of water through the skin; these            nutrients to the maternal body at the expense
together normally amount to < 10% of the           of the placenta and fetus.
animal’s resting rate of heat production and           For the second and subsequent breeding
are unavoidable, even in cold weather. In hot      cycles, practical guides for mating weights are
weather, evaporative heat loss is increased        80 and 100% of estimated mature weights. The
reflexly as a result of sweating and panting        body condition of the ewe, which is often eas-
and can rise to two or three times the resting     ier to estimate than weight, is also a valuable
metabolic rate. This is vitally important in hot   index in the implementation of feeding strate-
environments where evaporation may be the          gies. It has the added advantage that for many
only means of heat loss, especially if heat pro-   sheep breeds there is a positive correlation
duction is elevated due to work or by produc-      between the number of lambs born and the body
tion of milk, eggs, etc., or by growth, and        condition of the ewe at mating. Thus the level of
when the animal may additionally be subjected      lamb production and therefore the feed require-
to solar radiation. To be effective as a means     ments for pregnancy and lactation can be con-
of cooling, sweat must be evaporated from          trolled by manipulating body condition at
the skin surface; sweat that runs off the skin     mating. The estimation of body condition
and drips to the ground as liquid provides no      involves palpation of the ewe over the lumbar
cooling. Some animals, e.g. pigs, voluntarily      region and ascribing a score (based on a 0–5
increase evaporation by wallowing to wet the       scale) for the degree of fat cover over the trans-
skin surface when water, mud or damp bed-          verse processes of the vertebrae (Russel et al.,
ding is available to them.              (JAMcL)    1969). For most breeds, maximum ovulation
See also: Climate; Environmental tempera-          rate and therefore the potential for maximum
ture; Thermoregulation                             lamb production occurs with a condition score at
                                                   mating of 3–3.5. This level of body condition is
Ewe        A female sheep capable of breed-        characterized by transverse processes that have
ing. Ewes are usually categorized by age.          a smooth and rounded feeling; firm pressure is
Those mated in their first year are referred to     required to feel over their ends and the eye mus-
as ewe lambs; between 1 and 2 years of age         cle areas are full with a moderate degree of fat
they are called yearlings, shearlings or ‘two-     cover. The ideal follow-up feeding strategy for
tooths’, and thereafter adult or mature ewes.      ewes in this body condition at mating is one that
                                          (JJR)    maintains body weight and condition for the first
                                                   month of pregnancy, followed by a gradual
Ewe feeding          A priority in ewe feeding     move to a mild energy deficit, equivalent to a
is to enable the ewe to achieve a predefined        loss of up to 0.5 units of condition score, from
level of production with minimal risk to her       the end of the first to the end of the third month
well-being. In some sheep systems the aim of       of pregnancy. In general this small energy deficit
the feeding regimen is to promote full expres-     increases the size of the placenta, which is in its
sion of the ewe’s genetic potential for the pro-   rapid growth phase at this time. Provided that
duction of specific products such as meat,          the plane of nutrition during the remainder of
wool or milk. In others the goal is lower levels   pregnancy is increased to meet the nutrient
of output commensurate with a reduced avail-       requirements of the rapidly growing fetus or
ability of food. The application of appropriate    fetuses, the end result is slightly larger and more
feeding regimes for specific systems is facili-     vigorous lambs at birth; the bigger placenta also
tated by setting targets for body weight and       enhances mammary gland development, thereby
condition score during key stages of produc-       increasing the potential for milk production.
tion. For example, ewes bred in their first year        An important component of ewe feeding
should have attained 60% of their estimated        for the full expression of production potential
                                                Ewe feeding                                              193




The application of appropriate feeding regimes is facilitated by setting targets for bodyweight and condition
score during key stages of production.

relates to the adverse effects on ovulation rate        ‘swayback’ arises from copper deficiency in
of undernutrition approximately 6 months                utero, while subclinical cobalt deficiency during
prior to mating. This corresponds to the time           early pregnancy results in the birth of lambs that
that ovarian follicles leave the primordial pool        are slow to stand and suck; they also have a
and become committed to growth. In many                 reduced acquisition of passive immunity as mea-
production systems it also corresponds with             sured by their low serum IgG concentrations
peak lactation and an associated negative               (Fisher and MacPherson, 1991). During the
energy balance in the ewe. Fortunately the              later stages of pregnancy an inadequate intake
adverse effect of this negative energy balance          of selenium by the ewe results in the birth of
on ovulation rate can be avoided by a pre-              lambs with reduced vigour and a suboptimal
mating increase in nutrition (flushing), which           ability to generate heat from their brown adi-
sustains ovulation rate by minimizing the num-          pose tissue. Many of the trace element deficien-
ber of gonadotrophin-responsive and -depen-             cies become more prevalent following the
dent follicles that are lost from the ovulatory         increase in pasture production that occurs after
pool through atresia.                                   land drainage, additional fertilizer nitrogen
    Some nutritional effects are irreversible. For      usage and increases in soil pH. The causal
example, undernutrition during early fetal life         mechanisms are a reduced plant uptake of trace
disrupts the normal development of oogonia in           elements, the demise of pasture species rich in
the fetal ovary, thus providing an explanation          the elements and the higher trace element
for the reduction in adult reproductive perfor-         needs of ewes whose production potential has
mance in ewe lambs conceived and born in                been stimulated by increased feed availability.
harsh nutritional environments. Similarly,              Reduced maternal tissue mobilization arising
adverse effects on adult wool production have           from the general improvement in the energy
been recorded as a result of undernutrition dur-        and protein status of the ewe also contributes to
ing the last trimester of pregnancy in breeds           the problem by inhibiting the release of essential
such as the Merino, which has high genetic              mineral elements from the ewe’s body reserves.
potential for wool growth. Other examples of            Pre-lambing calcium deficiency (hypocalcaemia)
nutritional effects in utero on later performance       provides another example of this phenomenon.
involve trace elements. Enzootic ataxia or              Heavily pregnant ewes receiving adequate
194                                          Ewe lactation




amounts of calcium in their diet are extremely        nutritional management of the flock plays a
susceptible to hypocalcaemia following a sudden       central role in its productivity.     (JJR)
drop in calcium intake. The reason for this is
that the adjustments in gut absorption and            References
                                                      Donaldson, J., van Houtert, M.F.J. and Sykes, A.R.
mobilization of calcium from bone, which are
                                                          (2001) The effect of dietary fish-meal supple-
needed to prevent a fall in blood calcium, do             mentation on parasitic burdens of periparturient
not occur quickly enough to maintain calcium              sheep. Animal Science 72, 149–158.
homeostasis when dietary intake falls.                Fisher, C.E.J. and MacPherson, A. (1991) Effect of
    High-input systems maximize production                cobalt deficiency in the pregnant ewe on repro-
potential with minimum dependence on body                 ductive performance and lamb viability.
reserves; in contrast, low-input systems that are a       Research in Veterinary Science 50, 319–327.
feature of harsh nutritional environments involve     Russel, A.J.F. (1984) Means of assessing the ade-
major depletions of body lipid and mineral ele-           quacy of nutrition of pregnant ewes. Livestock
                                                          Production Science 11, 429–436.
ments to sustain production. For these systems it
                                                      Russel, A.J.F., Doney, J.M. and Gunn, R.G. (1969)
is important that energy deficits in late pregnancy        Subjective assessment of body fat in live sheep.
do not lead to excessive rates of body lipid mobi-        Journal of Agricultural Science, Cambridge,
lization and associated elevations in blood               72, 451–454.
ketones (3-hydroxybutyrate concentrations) above
0.8 nmol l 1 (Russel, 1984), otherwise there is a     Ewe lactation          The milk produced by lac-
high risk of pregnancy toxaemia with the loss of      tating ewes may be used either for the produc-
both ewe and lambs. To prevent blood ketones          tion of lambs or, via milking, to provide milk
rising above this threshold means restricting         and milk products (yoghurt, cheese and now
average       daily      energy      deficits     to   pharmaceutical proteins) for human consump-
    25 kJ ME kg 1 body weight or 2 MJ for a           tion. Milking usually follows a period (1–2
75 kg ewe bearing twins in which the daily            months) of suckling until the lambs can survive
metabolizable energy requirement 2 weeks              and grow on solid food alone. In some systems
before lambing is        18 MJ (≅ 1.7      mainte-    lambs are removed within 2 days of birth and
nance needs of the ewe pre-mating). For ewes          ewes are milked for the next 6–7 months. Alter-
at the limits of their energy deficit during late      natively, following the first few days of suckling,
pregnancy there are major nutritional benefits         ewes may be milked with the lambs restricted to
in feeding a small amount (1 g kg 1 ewe body          daily sucking periods after milking until weaned
weight day 1) of a protein supplement such as         at about 2 months of age, after which the ewes
fish meal. This protein source is rich in essen-       are milked for another 3–4 months. Durations
tial amino acids that escape degradation in the       of lactation therefore vary from approximately
rumen and are therefore available for absorp-         3–4 months for lamb-rearing systems to 6–7
tion in the small intestine. Its presence in the      months for dairy systems, which use breeds
diet allows body fat reserves acquired prior to       such as the East Friesland and Awassi that are
mating to be utilized more efficiently and safely      noted for their high milk yields.
for pregnancy; it also enhances colostrum pro-            In addition to ewe genotype, there are
duction and the ewe’s ability to combat gas-          numerous other non-nutritional factors that
trointestinal parasites (Donaldson et al., 2001).     affect milk yield. These include the positive
    Output from extensive systems is often dic-       effects of the number of lambs carried during
tated by available feed resources (natural plus       pregnancy as well as the number reared. In
supplements) during late pregnancy and early          the ewe, almost all of the udder’s secretory
lactation when nutrient demands are greatest.         tissue is laid down during pregnancy. Thus
The magnitude of these demands is set by the          the effect on milk production of litter size
plane of nutrition and body condition of the          during pregnancy arises from the increase in
ewe at mating. Pre-mating improvements in             the size of the placenta and the accompany-
nutrition (flushing) can increase the average lit-     ing stimulatory effect on mammogenesis of
ter size of ewes that are in poor body condi-         its associated greater production of hor-
tion (score 1.5) from 1 to 1.3, while a one unit      mones, notably placental lactogen. The effect
increase in condition score to 2.5 can increase       on milk yield of the number of lambs reared
it to 1.6. Thus the post-weaning to pre-mating        is greatest between singletons and twins; milk
                                           Ewe lactation                                       195




intake by singletons is usually well below the         With regard to the contribution that mobi-
ewe’s production potential and thus ewes           lized body tissue makes to energy needs for
rearing twins produce about 40% more milk          lactation, AFRC derived a dietary ME equiva-
than those with singletons. Further incre-         lent of 31.6 MJ kg 1 liveweight loss for a kl of
ments in yield for triplets and higher multiples   0.63, i.e. a diet with an ME concentration of
are generally much smaller (approximately          11.5 MJ kg 1 dry matter (DM). The corre-
15–20%); they also occur early in lactation        sponding CSIRO value was 28 MJ kg 1
and gradually decrease so that by 12 weeks         weight loss. In contrast, INRA linked the
differences in yield due to the number of          extent of body energy mobilization for milk
lambs suckled are negligible. At this point        production to a proportion of maintenance
daily yields have declined from a peak of          and adopted a value of approximately 70% of
about 4 l to about 1 l. In contrast, for dairy     maintenance (equivalent to approximately
breeds in which lamb suckling is replaced by       0.3 MJ of ME kg 1 W0.75 day 1) for early lac-
twice-daily machine milking during the sec-        tation, when the deficit between energy intake
ond month of lactation, the rate of decline is     and requirements is at its maximum.
slower, with yields not falling to 1 l day 1           Protein requirements for lactation are
until 20–25 weeks of lactation.                    expressed in terms of metabolizable protein
    Daily nutrient requirements during early       (MP). In the case of AFRC (1993) they were
lactation are the highest experienced by the       based on the assumption that ewe’s milk con-
ewe in her lifetime and are met through a          tains 48.9 g true protein kg 1 and its produc-
combination of increased appetite and the          tion from MP is achieved with an efficiency of
mobilization of body tissues. The extent of the    68%. Although other systems use different
appetite increase depends on the body condi-       efficiencies (CSIRO 70%, INRA 58%, NRC
tion of the ewe: fat ewes have smaller             65%), example calculations (Sinclair and
increases, and lose more body fat reserves,        Wilkinson, 2000) indicate that differences
that their thinner counterparts.                   between systems in the estimates of microbial
    Estimates of the energy requirements for       protein and the contribution of recycled nitro-
lactation can be obtained from the yields of       gen to the rumen lead to remarkably similar
milk constituents. For example, for meat-pro-      crude protein requirements. These are 169,
ducing breeds AFRC (1993) used the experi-         160, 167 and 154 g kg 1 dietary DM when
mentally derived relationship NEl (MJ kg 1) =      the AFRC, CSIRO, INRA and NRC systems,
0.04194F       0.01585P        0.02141L, where     respectively, are applied to a 70 kg ewe pro-
NEl = net energy requirement and F, P and L        ducing 2.0 kg of milk, consuming 2.1 kg DM
are the amounts (g kg 1) of fat, protein and       and 23.1 MJ of ME daily and maintaining a
lactose, respectively. Typical values are 70       constant body weight.
for F, 55 for P and 45 for L. CSIRO (1990)             During periods of body tissue mobilization,
used the coefficients 0.0381, 0.0245 and            which is the norm in early lactation, AFRC
0.0165 for F, P and L, respectively, whereas       (1993) assumed that each kilogram of weight
INRA (1989) used the relationship NEl (MJ          loss contributed approximately 120 g of milk
day 1) = 0.0588F        0.265, in which F is in    protein (enough for about 2.4 kg of milk)
g l 1. In converting net energy requirements       whereas CSIRO used the slightly lower value
for milk production to metabolizable energy        of 108 g. In relation to the amount of milk
(ME), all three feeding systems accept that        (approximately 4.3 kg) that can be produced
the efficiency (kl) of utilization of ME for milk   from the energy in 1 kg of weight loss, mobi-
energy production is influenced by the quality      lized body tissue is clearly deficient in protein.
or metabolizability (q) of the diet, i.e. q =      Ewes in negative energy balance therefore
ME/GE where GE = gross energy. AFRC                respond, in terms of extra milk production, to
and CSIRO used the relationship kl = 0.35q         increases in dietary protein. In fact, it can be
    0.420 whereas INRA used kl = 0.24q             argued that the aim should be to prevent body
0.463, which gives slightly higher values for      protein catabolism by ensuring that sufficient
kl than AFRC and CSIRO and therefore mar-          extra dietary protein (316 g MP kg 1 weight
ginally lower estimates of the ME require-         loss) is given to meet completely the milk pro-
ments for milk production.                         duction contributed from mobilized body
196                                         Ewe pregnancy




energy. This value is based on 1 kg of weight        Sinclair, L.A. and Wilkinson, R.G. (2000) Feeding
loss contributing enough energy for 4.3 kg of           systems for sheep. In: Theodorou, M.K. and
milk with a protein content of 5% and a 68%             France, J. (eds) Feeding Systems and Feed
efficiency of use of MP for the synthesis of             Evaluation Models. CAB International, Walling-
                                                        ford, UK, pp. 155–180.
milk protein.
    The requirements for the major mineral
                                                     Ewe pregnancy              Pregnancy in the ewe
elements, calcium and phosphorus, are based
                                                     lasts from the time of fertilization of an ovum
on the same general principles as for energy
                                                     or ova in the oviduct until the resulting con-
and protein. Their respective concentrations
                                                     cepta leave the uterus. In a successful preg-
in milk are 1.9 and 1.5 g kg 1 but conversion
                                                     nancy live lambs, with their associated
of these to dietary amounts, particularly in the
                                                     placentas, are born approximately 5 months
case of calcium, is not straightforward in that
                                                     after fertilization. The gestation length is nor-
there is an inverse relationship between intake
                                                     mally between 144 and 152 days but is to
and absorption; also mobilization of skeletal
                                                     some extent dependent on breed, nutrition
calcium and phosphorus is a normal occur-
                                                     and the number of lambs in the uterus.
rence during early lactation. AFRC (1991)
                                                         Ewes usually ovulate between one and four
provided a comprehensive set of dietary esti-
                                                     ova at each oestrous period. The numbers vary
mates for Ca and P in relation to ewe size,
                                                     according to the nutritional status of the ewe
milk yield and the metabolizability (q) of the
                                                     (see Flushing), age, season and breed. Some
diet. For calcium, the recommended dietary
                                                     breeds commonly carry one or two lambs,
concentrations for a 75 kg ewe consuming a
                                                     whilst others, such as the Border Leicester, will
diet for which q is 0.6 decrease from 0.38 to
                                                     often carry two or three lambs to term.
0.27% in the DM as her daily milk yield
                                                         Immediately after fertilization, the ovum
declines from 3.0 to 1.0 kg and her associ-
                                                     begin to divide, forming a solid cluster of cells
ated daily losses in body weight decline from
                                                     or blastomeres known as a morula (from its
100 g to zero. Corresponding recommenda-
                                                     mulberry shape). This process takes about 4
tions for dietary phosphorus are 0.41 and
                                                     days, during which the embryo continues its
0.30%. Unlike calcium and phosphorus
                                                     passage down the oviduct and enters the
reserves, magnesium reserves in the ewe’s
                                                     uterus. From about day 5 after fertilization, the
body are trivial and there is little, if any,
                                                     ovum hollows out to become a blastocyst,
response in Mg absorption as requirements
                                                     which consists of a single spherical layer of
increase. The lactating ewe therefore requires
                                                     cells, the trophoblast, with a hollow centre and
a constant dietary supply, particularly in the
                                                     an inner cell mass at one edge. The inner cell
first 6 weeks of lactation, when she is vulnera-
                                                     mass is destined to form the embryo, whilst
ble to death from acute hypomagnesaemia,
                                                     the trophoblast provides it with nutrients and
and particularly if she is grazing lush pastures
                                                     will form the fetal component of the placenta.
that are high in potassium and low in sodium.
                                                     At about day 6 the blastocyst ‘hatches’ from its
A common dietary supplement is magnesium
                                                     shell (the zona pellucida) and is elongating
oxide given at a daily rate of 7 g to ewes pro-
                                                     rapidly by about day 11. Meanwhile, the inner
ducing 3–3.5 kg milk day 1.                (JJR)     cell mass differentiates to form the germ lay-
                                                     ers, namely the ectoderm, mesoderm and
References
AFRC (1991) Technical Committee on Responses         endoderm. The ectoderm gives rise to the
   to Nutrients, Report 6. Nutrition Abstracts and   external structures such as skin, hair, hooves
   Reviews, Series B 61, 573–612.                    and mammary glands and also the nervous
AFRC (1993) Energy and Protein Requirements of       system. The heart, muscles and bones are
   Ruminants. CAB International, Wallingford, UK.    eventually formed from the mesoderm
CSIRO (1990) Feeding Standard for Australian         whereas the other internal organs are derived
   Livestock Ruminants. CSIRO Publications,          from the endoderm layer. By day 45, forma-
   Melbourne, Australia.                             tion of the primitive organs is complete.
INRA (1989) Ruminant Nutrition: Recommended
                                                         The embryo is able to exist for a short time
   Allowances and Feed Tables. INRA, Paris.
                                                     by absorbing nutrients from its own tissues and
NRC (1985) Nutrient Requirements of Sheep, 6th
   edn. National Academy Press, Washington, DC.      from the uterine fluids, but it ultimately
                                                   Exopeptidase                                       197




becomes attached to the endometrium by                    when energy requirements are very high. It
means of its membranes through which nutri-               is good practice to scan ewes to detect the
ents and metabolites are transferred from                 presence of more than one fetus, so that
mother to fetus and vice versa. The ewe pla-              extra feed can be given during the last 2
centa, unlike that of the cow, allows the pas-            months of pregnancy to ewes carrying mul-
sage of antibodies from the mother to the                 tiple lambs as well as to those with lower
fetus, so that lambs can acquire immunity from            body condition scores.
their dams in utero. The attachment process is                Severe underfeeding ultimately affects the
known as implantation and may begin as early              unborn lambs as well as their mothers. The
as day 10, but is not complete until around day           young may die in utero or have reduced via-
30. If the ewe is carrying more than one lamb,            bility after birth as a result of a lowered birth
the placentas and their blood supplies remain             weight and a possible lowering of milk yield.
separate. Thus, unlike the cow, there is little or        Severe malnutrition in early pregnancy may
no danger of sheep producing freemartins.                 simply reduce litter size. Protein, vitamin A
    Fetal growth is exponential throughout                and certain mineral and amino acid deficien-
gestation, the rate increasing as pregnancy               cies can cause fetal death. In the case of vita-
progresses. Fasting metabolism during preg-               min A the lambs may be affected even though
nancy is higher than that in non-pregnancy                the ewe remains healthy. Vitamin deficiency
and increases throughout pregnancy. This,                 may cause congenital deformities in fetal
together with the liveweight increase that                lambs that survive, while copper deficiency
should occur, leads to a gradual rise in the              can cause ‘swayback’, which can severely
maintenance energy requirement. Thus, the                 affect the coordination of newborn lambs.
requirement for energy in pregnancy is                        Increasing the energy intake of the ewe in
increased by far more than the calculated                 the last 6 weeks of pregnancy can increase
requirements for the storage of energy in                 the birth weight of lambs (see table). (PJHB)
the uterus. The fetus has a high priority for
energy and can draw specific nutrients from                Reference and further reading
the ewe’s body reserves even if she is being              AFRC (1993) Energy and Protein Requirements
underfed. Fetal lambs can, for example, be                  of Ruminants. CAB International, Wallingford,
adequately supplied with iron even when the                 UK.
                                                          McDonald, P., Edwards, R.A., Greenhalgh, J.F.D.
mother is anaemic, and a ewe can lose up
                                                            and Morgan, C.A. (1995) Animal Nutrition,
to 14 kg of her own body weight during
                                                            5th edn. Longman, Harlow, UK.
pregnancy and still give birth to normal
lambs. The fetus can maintain higher blood                Exercise: see Activity, physical
sugar levels than those of the ewe, which
can thus succumb to a hypoglycaemic condi-                Exopeptidase           A proteolytic enzyme
tion known as pregnancy toxaemia. Ewes                    that has the capability to hydrolyse the termi-
carrying more than one lamb are more                      nal peptide bonds in a protein. Aminopepti-
prone to the condition, which is also called              dases liberate amino acids consecutively from
twin lamb disease. The problem is exacer-                 the N-terminus. In contrast, carboxypepti-
bated by the fact that voluntary feed intake              dases act from the C-terminus and may also
tends to be suppressed in late pregnancy                  liberate di- and tripeptides.              (SB)

                The effect of energy intake of ewes in the last 6 weeks of pregnancy on the birth
                weights of their twin lambs. Source: McDonald et al. (1995).

                                   Energy intake       Liveweight change        Birthweight
                Group                 MJ/day              of ewes (kg)         of lambs (kg)

                1                       9.4                   –14.5                  4.3
                2                      12.4                   –12.7                  4.8
                3                      13.9                   –11.4                  5.0
                4                      18.6                    –5.4                  5.2
198                                         Exophthalmia




Exophthalmia            A common degenera-           increase the temperature and gelatinize the
tive condition of the eye in which the globe is      starch. Extrusion takes place in a compression
pushed out of the eye socket. In fish, it is typi-    chamber of variable length, normally at least
cally related to the enlargement of the choroid      2 m. The pressure is produced by feeding meal
gland of the posterior uvea or to degeneration       into the chamber at one end, whence it is
of the ocular musculature. It has been linked        moved along the chamber by a revolving screw
to niacin deficiency.                        (DS)     conveyor before being forced through a die
                                                     with many holes at the other end. The flow of
Extensive livestock systems               Live-      meal is adjusted to keep the conveyor running
stock systems, often based on natural grazing        full and obtain maximum pressure at the die.
or rangeland in dry areas, in which inputs and       Steam is normally injected along the length of
outputs are low. In large livestock operations,      the barrel to aid the extrusion process. Extru-
breeding is often carried out extensively, fol-      sion can be used to condition before pelleting,
lowed by intensive finishing of progeny for           but is more commonly used as a manufacturing
marketing. Extensive systems are not suitable        process in its own right. Extruded products are
for profitable smallholder livestock production.      commonly used as fish food, as the modifica-
                                           (TS)      tion of starch greatly improves the swelling
Extracellular water            Body water that is    properties in cold water. They are also used for
outside the cells, in contrast to intracellular      diets for young mammals and poultry, due to
water. Extracellular water includes that of          the improved digestibility of the starch. Most
blood, lymph, cerebrospinal and peritoneal flu-       dried pet foods now contain extruded chunks,
ids as well as interstitial water in the extravas-   since shapes can easily be made by changing
cular spaces within tissues. It can be estimated     the shape of the hole in the die.          (MG)
from the dilution of tracers that do not enter
                                                     Exudative diathesis           A disorder of
cells significantly during a short equilibration
                                                     poultry caused by selenium deficiency, usually
(e.g. bromide). Total body water is the sum of
                                                     as a result of consuming cereals with a low
extracellular and intracellular water.      (MFF)
                                                     selenium concentration. It is characterized by
Extract, ether: see Ether extract                    a generalized oedema, which arises from
                                                     abnormal permeability of the capillary walls.
Extraction, oil           Oil is extracted from      Usually the oedema first appears on the
oil-rich vegetable seeds, such as soybean            breast, wing and neck, with the greatest accu-
(20% oil), oilseed rape (46%) and linseed            mulation of fluid eventually forming under the
(39%), by first dehulling and then crushing the       ventral skin. Broilers are usually affected
seed between rollers or a screw press and col-       between 3 and 6 weeks of age, when they will
lecting the resultant oil. This process is known     lose weight, develop leg weaknesses and may
as expelling. The remaining solids are known         die. Supplementary selenium or vitamin E will
as expeller or ‘cake’ and have variable oil con-     prevent the disorder.                  (CJCP)
tents of around 10%. Many are sold and used
as animal feed ingredients in this state. The oil
                                                     Eye diseases           The eye is well protected
is a useful component of the material but it is
                                                     from variation in nutritional status but there are
susceptible to oxidation and therefore poses
                                                     disorders of the eye that have nutritional con-
potential storage problems. Further oil may be
                                                     nections. Vitamin A deficiency causes a dryness
removed by organic solvent extraction, which
                                                     of the conjunctiva (xerophthalmia) and can lead
reduces the oil content of the final meal to
                                                     to night blindness or complete blindness. Eyes
2–3%. The solvent is finally evaporated from
                                                     are susceptible to cancer during excessive
the meal using heat. The resulting oilseed
                                                     exposure to ultraviolet light, and foods with
meals are valuable vegetable protein sources
                                                     high levels of antioxidants protect against this.
for animals of all species.                  (MG)
                                                     Diabetes mellitus, arising from chronic hypogly-
Extrusion        A process in which condi-           caemia, can result in retinopathy, cataracts and
tioned meal is forced through an adjustable          glaucoma. In grazing animals, eye inflamma-
annular gap under high pressure. The high            tion, or conjunctivitis, can arise from irritation
shear forces created rupture the cell structure,     from seeds, chaff, awns, etc.              (CJCP)
                                              F

Factorial method (for estimating nutri-           anus. The amount and composition of faeces
ent requirements)             A method by which   vary between species and according to the
the requirement for a nutrient is estimated as    diet consumed. Faeces originate from undi-
the sum of its components. Depending on the       gested feed and endogenous losses (gastroin-
animal and the nutrient in question, these        testinal secretions and sloughed epithelial cells
components may include growth, activity, ges-     from the gastrointestinal tract) that have not
tation, lactation, egg production, wool           been reabsorbed. A considerable portion of
growth, etc. Dietary nutrients are used with      these may be transformed into microbial mat-
varying efficiency to meet these needs, and        ter. A large part of the electrolytes present in
these efficiencies must be included in the         the faeces are of metabolic origin.
assessment. For example, the energy require-          Faeces of non-ruminant animals are dom-
ment (R) of a growing animal is commonly          inated by bacterial cells, which may con-
considered to be the sum of its requirements      tribute up to 85%. Starch in faeces is
for maintenance (M), protein accretion (P) and    indicative of inefficient milling of cereals or
fat (lipid) deposition (F). Thus,                 of retrogradation. Faeces of ruminants con-
             R = M/km + P/kp + F/kf               suming mainly roughages are mainly cell wall
where km, kp and kf are the efficiencies with      components. The colour of faeces is derived
which dietary energy (usually metabolizable       from plant pigments and bacterially degraded
energy) is used for each process. It will be      bile pigments.
seen that the equation is used to derive a            The water content varies considerably
requirement for particular rates of protein and
                                                  within a species but is generally higher in
fat deposition; when these rates are inserted
                                                  the faeces of cattle (75–85%) than that of
into the equation, an estimate of the intake
                                                  pigs (65–75%) or even hens (70–75%),
required to support those rates is generated,
                                                  which secrete urine together with faeces via
though at some intake the animal’s potential
                                                  the cloaca. The pH varies with the composi-
for protein or fat deposition will be reached
                                                  tion of the diet and is generally below 7 in
and the linear responses will no longer apply.
    Such a simple model implies that efficiency    cattle and horses but above 7 in pigs, sheep
is constant at all intakes, which is often        and hens.
demonstrably untrue. More complex models              An abnormal water content of faeces is
allow for diminishing efficiency at higher         indicative of digestive disorders, in particu-
intakes. The simple model also applies only to    lar diarrhoea. Steatorrhoea is the excretion
an individual, whereas in practice the need is    of fatty, bulky, clay-coloured stools resulting
usually to derive the response of a population    from impaired digestion and absorption of fat.
(herd or flock) that comprises individuals with                                                (SB)
varying values for each of the terms. This
requires a more complex set of equations.         Faeces collection           Faeces are collected
                                          (MFF)   for many purposes, most commonly for mea-
                                                  suring nutrient digestibility or for investigating
Faecal flora: see Gastrointestinal microflora       effects on the microflora. Total collections are
                                                  made by confining the animal in a metabolic
Faeces       Also called stool. Waste matter      cage or by a container fixed around the anus
discharged from the intestines through the        or cloaca, usually with a harness. Simple

                                                                                                199
200                                     Fasting metabolism




‘grab’ sampling of the faeces can be used to       with one or more double bonds (unsaturated)
measure digestibility if a marker is added to      are often liquid at room temperature and are
the diet and if faeces samples are collected       called oils. Thus, fats and oils are similar in
systematically for a suitable period. Faeces are   structure but are either solid or liquid at room
often collected from fish by stripping, i.e.        temperature. Processed fat derived from pigs
pressing out the contents of the lateral intes-    is called lard. Processed fat from cattle, sheep
tine. In all digestibility studies a sufficiently   and horses is called tallow. Both of these are
long preliminary period, which depends on          solid at room temperature.
the transit time in the particular animal              To estimate the amount of fat in a feed or
species, is essential.                      (SB)   food, a sample is extracted for a specified
                                                   time with a solvent such as ether. In some
Fasting metabolism            Measurement of       cases, where total fat in a tissue is required,
an animal’s fasting metabolic rate is com-         a system based on a mixture of chloro-
monly used as an estimate of its basal             form/methanol is used. In the Weende sys-
metabolism. The animal must be pre-trained         tem of feed analysis, the fat component is
to the calorimeter and the actual measure-         defined as the ether-extractable material.
ment takes place over a prolonged period dur-      The weight of material extracted from a
ing which the animal is free to move within        known amount of sample is used to calculate
the confines of the chamber. The fasting            the percentage of the sample weight that is
                                                   made up of ‘fat’. However, not all ether-
period before the measurement begins should
                                                   extractable material is fat as defined above,
exceed that over which there is an observable
                                                   because other lipid-soluble materials are
heat increment following the last feed; in
                                                   extracted by ether. Fats used as food or feeds
ruminant animals this is 48 h or more.
                                                   come both from animals and plants. Animal
                                     (JAMcL)
                                                   products generally contain more saturated
See also: Heat increment of feeding
                                                   fats while plant products contain more unsat-
                                                   urated fats. Fat is a significant source of food
Fat metabolism: see Lipid metabolism               energy. The gross energy of fat is
                                                   37.7–39.7 kJ g–1 (9.0–9.5 kcal g–1), 2.5
Fat-soluble vitamins           There are four      times that of glucose.
fat-soluble vitamins: A, E, D and K. A defi-            Fats used for animal feeding are extracted
ciency of vitamin A results in defective night     either from animal carcasses, e.g. tallow, or
vision and keratinization of epithelial tissues,   from plant seeds, e.g. palm oil. Beef tallow is
e.g. in the eye (xerophthalmia) which can lead     no longer used since the occurrence of BSE.
to blindness. The lungs and gastrointestinal       Coconut oil and palm kernel oil are rich in
tract are also affected. A deficiency of vitamin    lauric acid (C12:0) and are sometimes
D results in rickets and osteomalacia, which       referred to as the lauric acid oils. Palm oil
involve a derangement of calcium and phos-         and tallow are composed mainly of palmitic
phorus metabolism. A deficiency of vitamin E        (C16:0), stearic (C18:0) and oleic (C18:1)
(an antioxidant) leads to tissue damage by         acids. The melting point of fats is determined
reactive oxygen species produced during aero-      mainly by the chain length of the fatty acids
bic metabolism. A deficiency of vitamin K           and their saturation. Fats with short-chain
results in haemorrhage, because vitamin K is       fatty acids or unsaturated fatty acids have
involved in the synthesis of the blood clotting    lower melting points than those with long-
factors.                                  (NJB)    chain saturated fatty acids. Saponification
                                                   value is an indicator of the chain length of
Fats        Esters of fatty acids with glycerol.   fatty acids in a fat or oil. High values indicate
Simple fats are called triacylglycerols or         shorter chain lengths. Iodine value is an indi-
triglycerides. Triacylglycerols with three satu-   cator of the degree of unsaturation of a fat or
rated fatty acids of ten or more carbons are       oil; high values are associated with a high
solid at room temperature. Those with fatty        proportion of unsaturated fatty acids.
acids of less than ten carbons or fatty acids                                            (NJB, JRS)
                                                  Fatty acid synthesis                                       201




Fatty acid composition (%) and physico-chemical properties of common fats.

Lipid                         Beef tallow        Lard        Coconut oil   Maize oil   Rapeseed oil   Palm oil

10:0                                                             7
12:0                                                            47
14:0                              3               2             17                                       1
16:0                             26              26              8           11              4          48
16:1                              6               4
18:0                             17              14             4             2              2          4
18:1                             43              43             5            24             56         38
18:2                              4              10             2            58             20          9
Melting point (°C)               40–50           28–48         23–26                                   38–45
S/U ratio                         0.85            0.72         13.29                                    1.13
Saponification value             190–200         193–200       251–264                                 196–202
Iodine value                     32–47           46–66          7–10                                   48–56

S/U ratio = ratio of saturated to unsaturated fatty acids.



Fattening          The term fattening (or ‘fin-                Fatty acid synthase              A multi-enzyme
ishing’) is used to describe the process of                   complex of seven enzyme activities responsi-
bringing animals to an appropriate stage of                   ble for the de novo synthesis of fatty acids. In
body condition prior to slaughter for meat                    biosynthesis of longer-chain fatty acids, two
consumption. As the animal grows towards                      carbon units derived mainly from the catabo-
maturity the parts of the musculature that pro-               lism of glucose and amino acids are added
vide the most desirable cuts of meat tend to                  two by two (i.e. via malonyl CoA to acetyl
be late developing and the subcutaneous and                   CoA) to make palmitate, which is a 16-carbon
visceral fat deposits increase more rapidly.                  saturated fatty acid, CH3·(CH2)14·COO–. In
The desired state of fatness (or ‘cover’) will                ruminants the source of the two carbon units
vary with the culture and consumer demand.                    is acetate from fermentative digestion in the
Furthermore, as the rate of protein deposition                rumen. The major site of fatty acid biosynthe-
decreases and the rate of fat deposition                      sis depends on the animal. In humans it is in
increases, the feed efficiency declines to a                   the liver, in rats liver and adipose and in birds
point where it becomes uneconomic to grow                     it is only in the liver.                   (NJB)
the animal to a higher weight. In developed                   Fatty acid synthesis             The process
economies, where the consumption of animal                    whereby fatty acids (for example, palmitate,
fat is generally regarded as detrimental to                   CH3·(CH2)14·COO–) are synthesized, mostly
health, there are usually grading systems in                  from non-fat sources (carbohydrate and amino
place with financial penalties for animals that                acids). Synthesis of fat is a means whereby
are considered to be too fat. In the case of                  excess energy from a meal can be stored in
pigs, grading is usually based on one or more                 the body for later use. The de novo synthesis
measurements of subcutaneous fat depth at                     of fatty acids occurs in the cytoplasm of liver
specified points on the carcass. Systems for                   or adipocytes, depending on the species.
cattle and sheep relate to visual inspection of               Acetyl-CoA (CH3·CO·SCoA), derived from
the extent and depth of subcutaneous fat                      carbohydrate or fat catabolism or from activa-
cover on the carcass. With poultry there is lit-              tion of acetate formed in intestinal fermenta-
tle external fat and even the fat content of the              tion, is the starting two-carbon unit for
meat tends to be low; the main source of fat is               long-chain fatty acid biosynthesis. Another
the abdominal fat pad, which is usually left in               acetyl-CoA is converted to malonyl-CoA by
the eviscerated bird.                  (KJMcC)                acetyl-CoA carboxylase, CH3·CO·SCoA +
See also: Carcass; Finishing; Meat composi-                   CO2 → HOOC·CH2·CO·SCoA and added to
tion; Meat production                                         the growing acyl-CoA chain as a three-carbon
202                                            Fatty acids




unit. After loss of CO2 from the added mal-           they are transported as free fatty acids. After
onyl-CoA a two-carbon unit has been added.