Factors affecting the reproductive performance of sows

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                                       Factors affecting the
                             reproductive performance
                                     of sows
                                                            Mike A. VARLEY
                                                University of Leeds - United Kingdom

There are many diverse factors which can have a criticism is directed. Different environmental
profound effect on the reproductive performance                      of conditions in addition to the imposition of good or
the breeding herd. Not the least of theseare: poor welfare to the animal, can alsobe associated
the genotype of the sow and boar, the health status with a different levelproductive efficiency.          of
of the herd and the general environment provided
for the breeding females. It is intended in this                          Light and temperature are two environmental
paper to concentrate on those factors which are componentswhichmayplay                                                        a r o l ei nt h e
under direct management control and which are                             determination of litter size although more datais
e c o n o m i c a l l ys i g n i f i c a n t .C o m p o n e n t so f      needed. Sainsbury (1971) has suggested that high
reproductive performance to be considered are:                            ambient temperature at mating associated with    is
lactation length, climatic and social environment poor litter size a t full term, although Tomes and
and prolificacy.                                                          Neilson (1979)have presented data showing this                        is
                                                                          notalways so. Obviously the effects of high
There has been progressive improvement i n recent                         ambient temperature on litter size in the female
years in sow productivity and this trend seems                            pig are confounded by effects on the male. Svajgr
likely to continue. Data from the Meat and                                 (1975) has demonstrated that high environmental
Livestock Commission show that over the years                             temperatures occurring two or three weeks after
1970-1984,sowproductivity                            in theUnited          mating are extremely detrimental to prolificacy.
Kingdom for all recorded herds rose from 15.5                              Table 1 presents data from a recent study by
piglets reared per sow per year to 20.0 reared per Wettermann and Bazer (1985) showing that heat
sow per year. There is great variation between                             s t r e s si nv e r ye a r l yp r e g n a n c yc a nh a v e
 herds in this respect and in 1984 the top 10% of detrimental effects on uterine function and the
herds weaning piglets between 14 and 18 days of development of embryos.
age were recorded as rearing 26.8 piglets per sow
                                                                                                 Table 1 Heat stress
per year (2.6 litters per sow per year;11.1 piglets                                                      ,
                                                                            after Wettermann& Bazer (1985) Pregnant Gilts
 born alive per litter). Not every producer can
achieve performances at this                  level but there may be

                                                                                                    I                    1
                                                                                                              Control          Heat stressed
 lessons to learn from these top herds which could
 help the  average farmer.

             I - Environmental effects                                    I  Embryowet
                                                                             weight per
                                                                             uterine horn
                                                                                                              336f75               233266

There is increasing concern about the effects of the                        3H Leucine
environment on the general welfare          of t h e                        incorporated in
breeding sow. Individual stalls, slatted floors and                         uterine explants
farrowing crates are but three examples where
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    The summer months and early autumn are the                         Table 2: Correlation coefficients between
    times when deficiency in the numbers of piglets                           reproductive performance
    born alive per litter is most likely to be seen. In                                    of
                                                                            and the quality stockmanship
    practice this means that inseminations for this                     from Hemsworth, Brand and Willems    (1981)
    period are carried out in the spring, not usually                 I             I              I                i
l                     of
    the hottest part the year. Changing         photoperiod                                          No. of piglets
    is likely to be another factor involved in seasonal                               Farrowing
                                                                                                       born per
    effects. The experimental data which exist refute                                      %
    this possibility (Greenberg and Mahone,           1982;
    Hacker and Perera,
    study to date has
                           1981; Mabry et al., 1982) In no
                        a significant effect of photoperiod
                                                                      IAversion          I
                                                                       score of sows          - 0.77             - 0.55
    on litter size been reported. Seasonal effects                     with humans
    therefore are still unpredictable and difficult       to
    understand fully.                                                         Many conclusions can be drawn from these simple
                                                                              observations, but it does seem that reproductive
    The social environment of breeding females (and processes in the sow are affected by good and bad
    boars)couldbeone                    of the most significant               stockmanship in the same way that milk yield in
    d e t e r m i n a n t s of reproductive efficiency and                                     be
                                                                              dairy cattle can influencedby the personalityof
    prolificacy. At the present time there is much                            the cowman (Seabrook, 1972). This relationship
    endeavour in the fieldanimal behaviour and the probably has some bearing the fact that adrenal         on
    pig is an excellent model for this. Moreover, with                        function,steroidhormonesandstress                 are
    the current awareness of the general public in                            inextricably linked together. Some individual
    matters of animal rights and welfare, there is a sows or some herds may be more stress prone OF
    need to understand the relationships involved in                          subjected to more stress via the system            of
    social interaction between animals in order that                          buildings and management than others. This
    we may develop systems                        of production and           manifests itself either as complete reproductive
    building designswhich fulfil1 the welfare needs of                        failure or reduced  profilicacy, and may account for
    the animal whilst still remaining                     productive.         much of the variability in litter size and hence
                                                                              overall sow productivity seen in practice.
    There is evidence that alterations to the social
    environment of sows and gilts can be responsible
    for changes in reproductive function. The group                     -      II Sow nutrition, body condition                and
    working a t Werribee in Australia has been very                                              prolificacy
    active in this area. Hemsworth, Beilharz and
    Brown (1978), for example, showed that sows
    housed in pairs between weaning and remating                                               a
                                                                              There has been n abundance of published reports
    had a higher litter size the next farrowing than over the last20 years regarding various aspects                              of
    sows housed individually.                                                 sow nutrition, body composition and reproduction.
                                                                              This work has provided a database from which
    I na d d i t i o nt oa n i m a ls o c i a li n t e r a c t i o n s ,      sound guidelines for the feeding of breeding
    Hemsworth, Brand and Willems                         (1981) reported a females have been derived.            I t is established
    man-animal interaction which influenced the                               practice to offer sows throughout pregnancy an
    litter size. These authors subjectively scored sows energy intake only a fraction above maintenance.
    from 12 separate herds for their "withdrawal" to Under average circumstances this                                     is a cost
    the human experimenters' approach. In those                               effective means of converting feedstuffs into
    herds in which sows showed decreased affinity                             weaners for sale.
    with humans, there were significantly fewer
    piglets born alive per litter.                   Table 2 gives the        It hasnow become apparent that although average
    correlation coefficients observed by Hemsworth et                                                                     sow,
                                                                              levels of energy intake suit the average there
    al. (1981) between the "aversion score" for each                          are too many animals without the middle band of
    farm in the study and either the farrowing rate                           body condition. It may be more efficacious at low
    percentage or the number of piglets farrowed per                          energy and protein intakes to carefully monitor
    litter. Those herds containing sows which showed individual sow body condition and adjust feed
    aversion to humans for whatever reason                               were scales accordingly. At this point in time, however,
    t h o s eh e r d sw i t ht h el o w e s tr e p r o d u c t i v e          the ideal body condition and body weight change
    performance.                                                              have not been. clearly identified for     the various

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phases of a sow's life. As far as prolificacy is             where Y = littersize(bornalive)and            X =
concerned, there is little doubt that the sow can            weaning age (days). In most the conclusion is
experience large variations in weight change                 drawn that with early weaning (7-20 days) there
without loss of numbers born alive per litter                are no benefits accruing in terms of annual sow
(Varley and Cole, 1978b; Hovel1 and McPherson,               productivity even though it is possible to produce
1977). At the extremes of body condition, the                2.8 litters/sow/year. The general recommendation
incidence of conception failure, anoestrus and               has been made that the optimisation of weaning
ovarian dysfunction are likely to increase.                  age is over the range three to four

There has been an ongoing debate over the last
                                                   The questionof when to weanis not so simple and
few years as to appropriate energy allowance for
                                                   there may in fact be many answers for different
sows and gilts in very early pregnancy (i.e. up to
                                                   farmers. Not the leastthe considerations the                    are
andaroundimplantation).Thequestion                of
                                                   available buildings on a particular farm and the
whether overfeeding in the immediate coitum
                                                   available management skills. Most people would
period causes increased embryonic mortality has
                                                   agree however that if sow productivity is the main
been open to much discussion. The evidence
                                                   goal then weaning at 21 days is the appropriate
indicates that at least in gilts, it is advisable to
                                                   age to wean. This conclusion does not alter
restrict daily feed intake in the first three weeks
                                                   significantly over a period time. What    of                 does alter
after mating (Dutt and Chaney,    1968).
                                                   is the optimum age to wean with regard to
                                                   financial performance. These relationships are
Evidence for multiparous sows has not been so
                                                   derived from a computer               model of the sow breeding
well defined but a recent study by Toplis, Ginesi
                                                   herd (Varley, 1985, unpublished) which                      integrates
and Wrathall (1983) showed whensowswere
                                                   all of the known biological facts and the                    economic
offered either 2 or 4 kg per day a diet containing
                                                   factors involved.The data                depicted in Figure 1are
13 MJ/kg of DE between 3 a n d 30 days post
                                                   for a new farm with an intensive building system
coitum, there were no differences in either the
                                                   and average to good management. It can be seen
number of viable embryosa t day 30 post coitum or
                                                   that physical productivity peaks at slightly less
in the percentage embryo survival rate. It may
                                                   t h a n a 2 0d a yl a c t a t i o nl e n g t h .F i n a n c i a l
therefore be prudent not to increase the daily
                                                   p e r f o r m a n c e ,i nc o n t r a s t ,s h o w sm a x i m u m
energy intake in very early pregnancy. But in
                                                   expression for a weaning ageof about 35 days. It is
multiparous sows there is often a real need to
                                                   interesting to note also that return on capital at
restore body condition losses resulting from the
                                                   current interest rates and price structures never
previous lactation. It should be possible to apply
                                                   shows a positive value.
an increased plane of energy intake following
mating without extra lossesembryos.
                                                   Figure 2 illustrates the point that financial and
                                                   physical performance peaked at the same pointas
               III Early weaning                   the pricing structure prevailing in 1975 (in the
                                                   UK a t least). The weanerprice/feed cost ratio was
                                                   much greater in the early                1970s. The optimum age
The application of early weaning over the last 20  to wean appears to change considerably over time
years hasplayed a major role in the increases seen and although it currently seems to be around five
in sow productivity on modern pig units. The       weeks of age, it may decrease if the economic
biological effects of early weaning are now well                                         is
                                                   situation changes. What needed are inexpensive
known: for example,as lactation length is reduced  creep diets for early-weaned piglets based soya                 on
there are concomitant effects on the interval from protein and other low cost ingredients. This will
weaning to conception, conception rates and the    not happen until our            knowledge of the nutrition of
subsequent litter size (Varley and Cole, 1978b). the young pig is much further advanced.
The problem with litter size       is probably the
biggest single drawback and the author has
                                                   Although most farmers pursue 25 piglets per sow
                                                   per year from a three week weaning system, they
relationship between weaning age and subsequent
                                                   may maximise their profits accepting 22 piglets
litter sizeis given by the equation:
                                                   from a five week weaning systemat today's prices
                                                   with current       knowledge.
                 Y = 6.8 1.1log, X

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                                                                                 profitability. Without a high order of prolificacy it
                                                                                 is i m p o s s i b l eo a x i m i s e n n u as o w
                                                                                                      tm             a        l
                       IV - Endocrine status                                     productivity. Survey data highlight the enormous
                       of early-weaned sows                                      variation that exists on farms and the best herds
                                                                                 achieve12.5pigletdlitterand                    at t h e o t h e r
                                                                                 extreme, the poorest record 7.8 (McIntyre, 1984,
        Recentworkhasfocusedontheendocrine                                       personal communicationMLC data).
        background of early-weanedsows(Varley,
        Atkinson and Ross, 1981; Varley, Peaker and
                                                                                 N e o n a t a 1m o r t a l i t y is a l s o of p a r a m o u n t
        Atkinson, 1984; EdwardsandFoxcroft, 1983).
                                                                                 importance. It is little consequence producing 12
        Plasma concentrations of the steroid hormone
                                                                                 piglets per litter born alive if 15% of these die
        progesterone do not differ in early pregnancy
                                                                                 within 48 hours of birth, asoften is the case. There
        between early-weaned sows and conventionally
                                                                                 are many management aids for reducing the
        teated sows (weaned a t six weeks) but there is
                                                                                 incidence of neonata1 deaths and these include
        evidence (Edwards and Foxcroft, 1983; Kirkwood
                                                                                 h i g ht e c h n o l o g yf a r r o w i n gc r a t e s , E . coli
        et al., 1984) that the luteinising hormone (LH)
                                                                                 vaccination and synchronised farrowing.
        surge at ovulation is significantly reduced for
        early-weaned sows. This could influence the
        timing of ovulation relative to other endocrine                          Supplementary rearing devices for the artificial
        signals, leading ultimately to early embryonic                           rearing of surplus piglets are now being used
        death. Surprisingly, the reduced peak does not                           widely in the UK. In otherwords, there are many
        affect the ovulation rate.                                               technicaloptionsopento     farmers with special
                                                                                 problems in this area.
        Oestrogens have been given some attention                           by
        Varley et al., 1984. Some sows have very high
        blood levels of circulating oestrogens between
        weaning and remating and in early pregnancy.
                                                                                                    VI - Conclusions
        transport and poor implantation of blastocysts.
                                                                                 From a practical viewpoint, there is a glimmer of
        The source this oestrogen is open at the                        moment
                                                                                 hope t h a t it may be possible in the future to
        to speculation but early-weaned                     sows show a very
        h i g hi n c i d e n c eo fe l e v a t e do e s t r o g e n s .      A
                                                                                 reproductive performances. There is a vigorous
        proportion of conventionally weaned sows show
                                                                                 effort beingmade by hybrid breeding companies to
        the same response but the overall incidence is
                                                                                 develop hyper-prolific female lines and Meat and
        much lower than for early-weaned sows.
                                                                                 Livestock Commission evaluations strongly
                                                                                 suggest that there are significant differences
        One possibility is that the oestrogens originate
                                                                                 between companies in breeding value                          of t h e i r
        from the adrenal glands. This known to occur as
                                                                                 animals for litter size. Producers now have the
        a reaction to stress. Itmay be that some animals
                                                                                 option to select a company’s gilts on the basis of
    .   are predisposedto stressand willproduce more
                                                                                 published comparative information. From the
        oestrogens as a result. Early-weaning tends to
                                                                                 starting point of agood genotype, it is t h e n
        compound together two very stressful events in
                                                                                 n e c e s s a r yt oa d h e r et ot h ee s t a b l i s h e d
        the reproductive life of a breeding female. These
                                                                                 recommendations of good husbandry and due
        are parturition and weaning. There is more work
                                                                                 consideration of some of the points listed below.
        to be done in this before firm conclusions are
        drawn but it does seem that elevated oestrogens
        may lead to embryonic deaths.                                            Use of an appropriate housing system with good

                 V - Prolificacy and neonata1                                    Stocking densityfor sows not too high;
                                                                                 Feed sows and gilts as individuals where possible
                                                                                 and monitorbody condition;
        Prolificacy, or the number piglets born alive per
        litter, is usually considered by most pig farmers
                                                        to         o                   ie       p
                                                           A v o i d v e r f e e d i n gn a r l y r e g n a n c y ,
        be the single most important determinant        of particularly with gilts and primiparous                sows.

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Consider the use a constant light pattern in dry Hovell, F.D. De B. and R.M. Macpherson, 1977. Thin sows. 1.
sow accommodation;                               Observations on the fecundity of sows when underfed for
                                                                        several parities. Agric. Sci.,Camb. 89:513-622.
Avoid high environmental temperatures between
weaning and mating and over the course early
                                                                        Kirkwood, P.N., K.R. Lapwood, W.C. Smith, andI.L. Anderson,
pregnancy; and
                                                                        1944. Plasma concentrations of LH, protein, oestradiol-l7 and
                                                                        progesterone in sows weaned afterlactation for 10 or 35 days. J.
Avoid the imposition of any stress on the animal,
                                                                        Reprod. Fert.70:95-102.
particularly at farrowing and between weaning
and service and in early pregnancy.
                                                                        Mabry, J.W., F.L. Cunningham, R.R. Kraeling and G.B.
                                                                        Rampacek, 1982. The effect of artificially extended photoperiod
T h i sl a s tp o i n tr e l a t e st ot h eq u a l i t y          of
                                                                        during lactation on maternal performance of the sow, J.Anim.
s t o c k m a n s h i pa sw e l l         as t om a n a g e m e n t
                                                                        Sci. 54918-921.
techniques. In recent years there has been an
increase in the ratioof pigs to stockman as herds
                                                                        Sainsbury, D.W.B, 1971. Climatic environment and pig
have increased in                 size. I t is of p a r a m o u n t
                                                                        performance. IN: Pig Production, ed. D.J.A. Cole, pp. 91-106.
importance to ensure that those still working in
                                                                        Buttersworth, London.
the industry are fully trained and of the highest
calibre. However good the genotype, the housing,
                                                                        Seabrook, M.F, 1972. A study to determine theinfluence of the
the feeding and the style of management, the
                                                                        herdman's personality on milk yield. J. Agric. Labour. Sci. 1:l-
primary constraint may always be the person
actually tendingto the animal'sneeds.
                                                                        Svajgr, A.G., 1975. Stretching the feed dollar. Feedstuffs.
In the future, with the introduction to Europe of
                                                                   March 17, p.14.
Chinese breeds capable of producing 16 to 20
liveborn piglets per litter, and with our increasing
                                                                   Tomes, G.J. and H.E. Nielsen, 1979. Seasonal variations in the
u n d e r s t a n d i n g of t h e , b a s i c m e c h a n i s m s
                                                                   reproductive performance of sows under different climatic
controlling embryonic mortality, it might yet be
                                                                   conditions. Wld. Rev. Anim. Prod. 15:(1) 9-19.
possible to sell 3,000bacon pigs a year from 100
                                                                        Toplis,P., M.F.J. Ginesi, and A.E. W r a t h a l l , 1983. The
                                                                        influence of high food levels in early pregnancy on embryo
                                                                        survival in multiparous,sows.Anim. Prod. 37:45-48.
Dutt, R.H. and C.H. Chaney, 1968. Feed intake and embryo
                                                                        Varley, M.A. and D.J.A. Cole, 1978a. The relationshipbetween
survival ingilts. Prop.Rep. Ky. Agric. Exp. Stu. No. 176:33-35.
                                                                        the weight changethe sow and her reproductive output.   Proc.
                                                                        Brit. Soc. Anim. Prod. 1978. Page 368 (abstr.).
Edwards, S. and G.R. Foxcroft, 1983. Endocrine changes in
sows weaned a t two stages of lactation. J. Reprod. Fert. 67:161-
                                                                        Varley, M.A. a n d D.J.A. Cole, 1978b. Studies. in sow
                                                                        reproduction. 6 . Theeffect of lactation length on pre-
                                                                        implantation losses. Anim. Prod. 27:209-214.
Greenberg, L.G. and J.P. Mahone, 1982. Failure of a 16 h L =
8hD or a 8hL = 16hD photoperiod to influence lactation or
                                                                        Varley, M.A.,R.E. Peaker, and T. Atkinson, 1984. Effect of
reproductive efficiency in sows. Can. J. Anim. Sci. 62:141-145.
                                                                        lactation length of the sow on plasma progesterone, oestadiol-
                                                                        17 and embryonicsurvival.   Anim. Prod. 38:113-119.
Hacker, R.R. and M. Perera, 1981. Effect of light changes on
swine reproduction. University of Guelph. Annual Report.
1981. pp. 21-23.                                                        Varley, M.A., T. Atkinson, and L.N. Ross, 1981. The effect of
                                                                        lactation length on the circulating concentrations         of
Hemsworth, P.H., R.G. Beilharz, and W.J. Brown, 1978. The               progesterone and oestradiol in the early-weaned sows.
importance of the courting                        on
                            behaviour of the boar the success           Theriogenology16:179-183.
of natural and artificial matings. Appl. Anim. Ethol. 4:341-347.
                                                                        Wetterman R.P. andF.W.Bazer,              1 9 8 5 . Influence of
Hemsworth, P.H., A. Brand, and P. Willems, 1981. The                    environmental temperature onprofilicacy of pigs..IN Control
behavioural response of sows to thepresence of human beings             of Pig Reproduction II. Ed. Foxcroft G.R., D.J.A. Cole, and B.J.
and its relation productivity. Livest.Sci. 8,67-74.                     Weir, J. Reprod. Fert.:Supplement 33.

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                  Figure 1 :Effect of weaning age oneconomic aspectsof pig production


                                                                S S MARQIH E/ 8 0 W                          -
                                                                                                            - i


 40                                                                                                               +S
              16                                                                                                   O
                                                                     RETURN ON CACltAL I                          -S

                                    10                 20                    30            40

                                                   WEANINQ AGE (days)
                       Figure 2 :The effect of weaning age profitability in Great Britain

      500     I

                             1975 .costs          X.       *
                   /-0                                         \ \
         3                                                               \


                                         Current Feed Costs              (C)
         3                               T9 8 5

                   I                 l                 *                     I         I                     1

                  14               21              28        35                       42                     49
                                                   Weaning Age (days)

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