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                          Broiler Nutrition Guide

This new and completely revised Broiler Nutrition Guide has been produced by Dr. Robert
Teeter, Professor at Oklahoma State University (OSU) and Dr. Chet Wiernusz, Nutritionist
in the Cobb-Vantress World Technical Support Group.

Data for the guide utilizes the extensive research on Cobb birds carried out over the last 20
years by Dr. Teeter’s group at OSU and various other research institutes. The format
therefore includes much explanatory material to allow better utilization of the data to match
the wide range of nutritional and growing strategies with varying environmental conditions for
broiler production worldwide.

Cobb-Vantress wishes to acknowledge this significant cooperation and contribution.


                                            1                                          COBB
                  Nutritional Guide
                Broiler Nutrition Guide

       1.   Broiler Nutrition                               2
       2.   The Bird Environment and Growth Interface       3
            COMPENSATORY GAIN                               5
       3.   Interfacing Management, Environment, and Growth 6
            MAINTENANCE                                     7
            BMR AS A MAINTENANCE COMPONENT                  8
            MAINTENANCE EXACERBATION COSTS                  9
            MAINTENANCE & IMMUNE CHALLENGE COST            10
            TISSUE GAIN                                    11
            MANAGEMENT                                     11
       4.   Quantifying the Production-Management Value    14
       5.   Optimizing the Performance Environment         16
            NONPATHOGENIC STRESS                           16
            AIR QUALITY                                    16
            AMBIENT TEMPERATURE                            16
            LIGHTING                                       18
            FEED FORM                                      18
            HYGIENE                                        19
       6.   Feed Conversion                                20
       7.   Growth as Proportion of Mass Versus Yield      22
       8.   Nutrient and Energy Recommendations            23
            BASIC NUTRIENT RELATIONSHIPS                   23
            ENERGY                                         23
            REQUIREMENTS                                   24
            PROTEIN NEEDS                                  25
       9.   Feeding for Yield and Lean Meat Production     26
            APPARENT CRUDE PROTEIN MAXIMUM                 27
            SUMMARY BROILER CRUDE PROTEIN NEED             29

          Broiler Nutrition Guide

10.   Vitamin and Trace Elements                           32
      RECOMMENDED NUTRIENT LEVELS                          32
      FREE RANGE CHICKEN PRODUCTION                        33
      YELLOW SKINNED BIRDS                                 34
11.   Feed Manufacture                                     35
      RAW MATERIAL QUALITY                                 35
      FEED HYGIENE                                         35
      FAT QUALITY                                          36
      PROTEIN QUALITY                                      36
12.   Feed Management                                      38
      RAW MATERIALS QUALITY AND TESTING                    38
      FEED TESTING                                         38
                SAMPLING                                   38
      WHOLE WHEAT FEEDING                                  38
13.   Physiological Stress                                 40
      HEAT STRESS (HS) GENERAL CONCERNS                    40
                HS / THERMOBALANCE                         40
                HS / EVAPORATIVE COOLING                   41
                HS / HEAT PRODUCTION                       41
                HS / MANAGEMENT OPTIONS                    41
                HS / WATER MANAGEMENT                      42
                HS / OTHER CONSIDERATIONS                  42
                HS / HYGIENE                               42
      ASCITES                                              43
                OXYGEN AS A NUTRIENT                       43
                ACTIVITY                                   44
                BASAL METABOLIC RATE                       44
                TISSUE ACCRETION AND NEEDS                 44

                DIETARY SODIUM                             45
                BIRD ABILITY TO CONSUME OXYGEN             45
                OTHER MEASURES                             47

                          Broiler Nutrition Guide

                           1. Broiler Nutrition
                Introduction and Definition of Objectives
Cobb broiler chickens are grown all over the world, under a broad range of agricultural
conditions, to produce numerous products. The agronomic conditions encountered by
producers include a diverse array of environmental, nutritional, mechanical and
immunological combinations. Due to these conditions, unique challenges may arise that
require nutritionist, veterinarians and facility managers working together to provide the
best possible production environment. Birds must be provided adequate housing,
hygiene, management, and nutrition to achieve their genetic potential and/or optimal
profitability. Despite the environmental challenges faced by some, successful broiler
production occurs every day throughout the world.

The purpose of this manual is to provide a guide containing the general specifications as
to the feeding and manufacture of broiler feeds that are applicable to a diverse array global
settings faced by producers. The tables of recommended nutrient levels are intended to
reflect the nutritional requirements of Cobb broilers under the most common as well as
some unique managerial and environmentally challenging production scenarios. The data
herein are directed towards interactivity between nutritional and managerial approaches for
optimizing bird performance. These recommendations are based upon a combination of
our own research, academic publications and practical experience of working with
customers around the world. We provide this guide as a supplement to your own skills in
feed manufacture and broiler management, to work in conjunction with your knowledge and
judgment to attain the best results possible. If the guide raises any questions and/or issues
that you wish to discuss, please contact Technical Services at Cobb-Vantress, Inc.

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                          Broiler Nutrition Guide

    2. The Bird Environment & Growth Interface
A bird’s ability to grow is determined by a combination of genetic, nutritional, environmental
and managerial variables. All aspects of providing broilers essential housing, dietary needs
and management should be related to their age influenced growth curve (Figures 1-3). As
the bird grows and matures, it’s environmental and nutritional needs change in proportion to
its age, body size, body composition and tissue accretion rate. The final productivity
outcome will be the summation of the bird’s genetic-environmental interactions as influenced
by the managerial and nutritional decisions made. The bird’s general growth and
performance curves improve each year. To optimize these curves management teams
endeavoring to provide the best possible environment, within the constraints of the region,
are apt to achieve the best possible results.

                         Figure 1. Live Body Weight vs. Age

         BWT (g)




                 0          10        20          30        40        50
                                 Birds Age (days posthatch)
 Figure 1. A plot of bird live body weight (BWT) vs. day of age illustrates a rapid growth
 potential. Though growth appears slower in the early days, a day-old chick has the
 potential to more than double its live body weight after just a few days of life. During this
 time bird dependency upon its environment is greater than at any other point in the
 production cycle.

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                              Broiler Nutrition Guide

              Figure 2.     Live Body Weight                          Figure 2.
                          vs. Feed Consumption                        The     shape     of
 BWT (g)                                                              the growth curve
 3000                                                                 changes       when
                                                                      viewed versus feed
                                                                      Though age is
 2000                                                                 important,    many
                                                                      companies      feed
                                                                      birds according to a
 1000                                                                 preset amount of
                                                                      feed to establish
                                                                      production phases.

         0             1000           2000            3000     4000
                              Feed Consumption (g)
                  14     28         42       49          55
                       Typical Bird Age (days)

                          Figure 3. Average Daily Gain
                             vs. Feed Consumption
       ADG (g)





              0                1000          2000             3000       4000
                                  Feed Consumption (g)
 Figure 3. As the bird matures, its rate of daily gain (ADG) rises to a near maximal
 level and plateaus. These values are actual daily gain, not merely ending weight per
 day of age. Beker & Teeter, OSU

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                          Broiler Nutrition Guide

                                Compensatory Gain
When growth is suppressed due to stress, it is possible for at least a partial recovery under
the right conditions. For example, high ambient temperature can subsequently reduce the
performance of poultry and livestock classes. However, if the stressors are alleviated, there
is potential for compensatory gain or catch-up growth. The birds referenced in Figure 4 were
raised under hot conditions from days 19 to 31. Taking a sub-sample of the birds and placing
them in a thermoneutral environment for days 31-49 enabled them to nearly reach the live
weight of their continually thermoneutral housed counterparts and exceed the performance
of the continually heat stressed group.

                       Figure 4. Growth Response
                       Following Stress Removal
                Body Weight (g)
     1700                                                              CG
     1500                                                              HS
         19 21 23 25 27 29 31 33 35 37 39 41 43 45 47

                             Days Posthatching
Figure 4. Male broilers reared under heat stress conditions have suppressed growth.
Moving the birds to an acceptable environment enables them to nearly catch the
continually thermoneutral housed birds. Qureshi, Daskarin and Teeter, OSU

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                          Broiler Nutrition Guide

 3. Interfacing Management, Environment & Growth
Many aspects of management classically referred to as animal husbandry, merge with
environment to influence expression of genetic growth potential. Numerous studies have
been conducted to identify critical variables. Though the number of variable candidates is
high, they can be grouped to simplify the application process. A working model relating the
practical aspects is as follows:


BMR                               SUBSTRATE                       HOUSING
ACTIVITY & SUBSTRATE               EFFICIENCY                     NUTRITION
  EFFICIENCY                      ACTIVITY                        HEALTH
STRESS                                                            HUSBANDRY
  Ambient Temperature
  Immune Response

The maintenance (M), tissues gain (TG) and management (MGT) terms are interactive and
multifaceted; however, this does not preclude their quantitative measure or producer
influence to enhance both the rate and efficiency of production. Terms are written as + to
reflect the fact that each is a variable and should be viewed with the potential to enhance or
hinder performance. Tissue gain is written after maintenance to reflect that maintenance
components will generally be satisfied prior to tissue accretion. As such, an elevation in bird
maintenance needs will divert nutrients away from growth, unless feed intake is also
enhanced. Management is included as a variable. Relative to the current production state
managerial decisions can have a positive or negative influence on both M and TG. As such,
certain aspects of management are quantifiable components that have influence upon both
the extent and efficiency M and TG. The quantitative values expressed in this writing, as in
Figure 5, are written relative to performance in a generally good production environment and
may be viewed as benchmarks of relative value differences between production scenarios.
Each term will be the focus of discussion at various segments throughout this manual.

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                         Broiler Nutrition Guide

                Figure 5. Consumed MEn Partioned into Tissue
 ME n Consumption (kcal)




                0                         10000                       20000
                                      ME n Consumption (kcal)

 Figure 5. Consumption of MEn (green), under good growing conditions, is partitioned as
 kcal live retained energy (yellow) and kcal energy utilized for maintenance (red). Each
 component is multifaceted with potential to enhance or hinder performance. Diversion of
 energy into maintenance reduces energy for gain and increases FCR. Likewise,
 inefficient dietary substrate conversion into body tissue will increase the FCR ratio.
 Management will strongly influence maintenance and tissue gain proportions to MEn
 consumption. Beker and Teeter, OSU

A working definition of maintenance is the amount of energy and nutrient required to sustain
an animal with no net gain or loss of body tissues. Housed within the maintenance category
is basal metabolic rate (BMR; energy expended by a broiler at rest and performing no
thermal work due to environment), activity energy expended by the bird to attain sustenance,
inefficiency of consumed nutrient oxidation for satisfying maintenance needs (waste heat
production) and stress defined as any challenge necessitating extra energy expenditure to
maintain homeostasis. The maintenance value is the sum of its components and is thereby
influenced by each contributing factor. On average, in a good production environment,
maintenance is about 36% of MEn consumption.

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                         Broiler Nutrition Guide

   Figure 6. Maintenance Energy Partioned by Components
 ME n Consumption (kcal)




                  0                       10000                      20000
                                     ME n Consumption (kcal)

 Figure 6. The kcal needed to satisfy the maintenance fraction (yellow), lying within
 overall kcal of MEn consumption (green), may be partitioned into the major classes of
 BMR (black) and kcal expended for activity + waste heat associated with substrate
 oxidation (red) expended in satisfying maintenance. Maintenance in a good growing
 environment is about 52% BMR and 42% waste heat. This corresponds to 19 and 17 %
 of overall MEn consumption, respectfully. Beker and Teeter, OSU

                      BMR as a Maintenance Component
The building blocks of energy metabolism start with homeostasis of existing tissue. As
displayed in Figure 6, basal metabolic rate (BMR) increases linearly with cumulative MEn
consumption and averages about 36% of consumed MEn. Basal metabolic rate (kcal),
however, is curvilinear with respect to body mass as heat dissipation is related to surface
area (Figure 7).

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                         Broiler Nutrition Guide

                    Figure 7. BMR Versus Body Weight
  BMR (kcal)




             0                 1000                 2000                 3000
                                         BWT (g)
 Figure 7. Energy expended to satisfy bird BMR, increases in a curvilinear fashion with
 live bird weight. This energy value may be impacted by numerous factors. Beker and
 Teeter, OSU

                 Maintenance Activity and Waste Heat Cost
A portion of the maintenance energy expended is related to the activity required to attain
sustenance. Additional energy expenditures in this category include waste heat associated
with the digestion and substrate metabolism to the needed form. In the current model they
are combined as their fractional estimation is speculative. Energy expenditures here enable
the bird to compete in the production environment. Managerial decisions related to house
design, feeder and waterer space, distance between feeders and waterers, stocking density
and lighting are among the many variables potentially influencing this component. A
combined estimate of maintenance energy and waste heat costs generated within an
adequate production environment, is 17% of MEn consumption.

                      Maintenance Exacerbation Costs
Various stress categories have the potential to adversely reduce performance. Among
variables included in this category are factors such as ambient temperature and relative
humidity extremes, immunological response, atmospheric contaminants (ammonia, dust,
brooder gases), fear and discomfort. Managerial factors influencing these components of
maintenance range from overall house design and ventilation to the hygienic environment
and general husbandry.

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                          Broiler Nutrition Guide

             Ambient Temperatures & Relative Humidity Cost
From a practical vantage, divergence of ambient temperature (AT) from the zone of
thermoneutrality can significantly elevate maintenance cost. Relative humidity has the
potential to exacerbate the AT impact. Managerial decisions regarding housing design,
brooder application and day to day regulation of ventilation equipment will each influence the
magnitude of the AT + RH challenge to the chick. Figure 8 illustrates the impact of ambient
temperature deviation from the thermoneutral environment at constant RH on bird energy
expenditure for body weight homeostasis of 5 day-old chicks.

                  Figure 8. Maintenance Heat Production
                       Due to Temperature Change
             -5     -4     -3     -2    -1        0    1      2      3      4      5

                                       TCHANGE (C)
 Figure 8. Heat production (HP, kcal/day/kg) of 5 day old chicks, fed at maintenance,
 increases under conditions of changing ambient temperature. Both decreasing and
 increasing ambient temperature from TN (TCHANGE=0) results in elevated heat
 production. Maintaining the environment at TN will improve FCR as less energy is
 diverted from growth. In this example, a 5 C temperature change elevated maintenance
 energy expenditure by 30% for the 5 day old chicks. This would divert nearly 11% of
 consumed MEn to nonproductive purposes if feed consumption remained constant.
 Beker and Teeter, OSU.

                   Maintenance & Immune Challenge Cost
Though the extent of energy expended by immune challenge varies, the data in Table 1
indicates that an E. coli challenge diverts energy away from performance. In this study,
chicks were limit fed at 5% of their initial 7 day body weight such that variation in feed
consumption with challenge would not mask heat production differences. The E. coli

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                          Broiler Nutrition Guide

challenge resulted in an 8% elevation in heat production and a 7.3% increase in O2
consumed. However, analysis over additional feed consumption levels estimated the
maintenance MEn elevation at just 2.9%. The disparity between the two measures may
reflect differences in retained tissue composition. Nonetheless, it is clear that immune
challenge has a calorific and oxygen consumption cost.

Table 1. E. coli challenge effects in limit fed chicks.
    Treatment      Gain (g)           Feed       O2 Cons                 Heat Production
                                 Consumption (g) (L/h)1                       kcal/h

     Control           -12               79.9              0.587b               2.97b

     E. coli           -19               79.9              0.630a              3.17a

Beker, Daskarin and Teeter, OSU
                                      Tissue Gain
The energy available for gain may be computed as MEn consumption minus maintenance
energy cost as displayed in Figure 5. This energy gain must support all activities and
metabolic needs exceeding maintenance for tissue accretion. The result, as displayed in
Figure 9, is the lean tissue + water and lipid accrued. Note that once water is removed from
lean tissue that the actual amount of protein gain is markedly lowered. This is why the
fractional gain for protein and fat has a significant impact upon feed conversion. On average,
for a corn-soybean based ration, approximately 66% of MEn consumption is available for
direct deposition in lean and lipid tissues.

Though the energy and nutrient content of tissue may be directly measured, the efficiency
of nutrient conversion into tissue varies with the type of tissue being synthesized and the
substrate being employed. For example, energetic efficiency of converting digestible protein,
carbohydrate and lipid into de novo lipid is 45, 78 and 84%, respectively. Managerial
decisions regarding ration composition influence overall efficiency of substrate conversion to
tissue, as do the managerial decisions impacting activity exceeding maintenance. Tissue
gain is the purpose of poultry production; however, it is the component occurring virtually by
default after maintenance activity and waste metabolic heat have been removed.

Managerial influences, under the proposed model, strongly impact both the M and TG
categories. As shown in Figure 5, maintenance energy expenditure accounts for approximately
36% of MEn consumption under good growing conditions. Data displayed in Figure 5 also
suggests that this amount may increase by 30% under conditions of AT stress to divert as
much as 10% energy from TG unless feed intake is elevated. However, if managerial input
through enhanced ventilation and/or evaporative cooling reduces the elevated AT rise then the
loss will be partially ameliorated. Ambient temperature is merely one aspect of the
managerial and maintenance interaction that impacts TG. Other managerial influences
may range from such simple factors as stocking density and feeder space to minimizing
waste heat production via control over dietary nutrient balance and/or lighting program.

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                           Broiler Nutrition Guide

            Figure 9. Live Body Weight Partitioned into
       Lean, Protein and Lipid Tissues vs. MEn Consumption
       BWT (g)



              0   1    2    3    4   5    6        7   8   9   10 11 12 13
                                      (in thousands)

                                 ME n Consumption (kcal)

 Figure 9. Approximately 66% of MEn consumption is available for live weight accretion
 (black, g). Within the live mass, energy deposition occurs as lean + water (yellow),
 protein (green) and lipid (red) components. Metabolizable energy not utilized for
 accretion is largely used for maintenance and activity. Beker and Teeter, OSU

  Various lighting programs have been applied to laying and breeding poultry to optimize
  egg production. More recently such programs have also been applied to broiler rearing.
  Light availability in duration and intensity have been observed to impact the efficiency of
  production with reports of improved FCR, body weight gain and the lowered incidence of
  metabolic disorders. The underlying mode of action may be reduced energy expenditure
  for activity. When the lighting is reduced, birds are almost immediately observed to
  reduce their activity, consume less oxygen and produce less heat. Conversely, when
  birds under a state of BMR (usually measured in the dark), are exposed to light their
  oxygen consumption rises by nearly 3% when feed is not present. The data presented in
  Figure 10 displays the reduced heat production observed for a flock on a program of 12
  hours light followed by 12 hours of dark. These differences were entirely eliminated when
  a program of 23 hours of light with 1 hour of dark was utilized.

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                        Broiler Nutrition Guide

Figure 10. Lightening               O2 Consumption
Program Affects on                     Liters/Hour
Oxygen Consumption                                                  0
for broilers in the                   0.7                             11
                                                                  0 111
growing phase                                                     111
Figure 10. Lighting programs                                   111
have the potential to conserve                                111
energy by reducing activity                                  101
expenditures. However, note that      0.6                     11
lighting programs differ markedly                          11
in their impact upon the bird’s                          1110
oxygen consumption (liters/hour).                      1111
The plot at the top is for birds
exposed to 23 hours of light per
day and 1 hour of dark. The                                       11
lighting program at the bottom is                            11111111
for birds       experiencing 12       0.7                    1111
consecutive hours of light                               1111      000
followed by 12 hours of dark.                          1111     000000
                                                     1111    00000
Birds managed with 12 hours of
                                                  111111    0000
darkness had the same final live
                                      0.6                0000
weight and significantly improved                   000000
FCR.         Lighting     program                000000
interaction with environment and
stocking density should be
anticipated as time must be
allowed         for all birds to            0    100        200          0
adequately consume feed. Beker
and Teeter, OSU                                        Hours Post Test Initiation

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                          Broiler Nutrition Guide

4. Quantifying the Production-Management Value
Chief among management decisions is the intent of enhancing profitability. This can be a
quite challenging process, as performance improvements must be transferred into an
economic picture. In most companies, final bird performance is commonly expressed as a
live weight and feed conversion. Managerial decisions, in turn, must be quantified as to their
impact upon live body weight and feed conversion. If the live weight and/or feed conversion
consequence of a stressor is known; and the management cost of solving the issue can be
quantified, this value may be compared with the projected nutritional cost for eliciting the
same production change. The relationship, displayed in figure 11, enables the live body
weight-feed conversion variable to also be expressed as a dietary caloric density response
throughout the growth curve. The basis for this relationship is that both body weight gain and
feed conversion are responsive to caloric density (constant calorie/protein ratio). These
relationships allow field data and management decisions to be transformed into an interactive
picture of environment, bird performance, management and nutritional cost. In this manner
decisions impacting production cost and output benefits may be judged as nutritional
equivalence. As such, calorific value may be applied to managerial decisions regarding
lighting programs, feed form, ventilation and hygiene among others. Thus providing the
opportunity to make improvements by multiple methodologies, or enabling the relaxation of
nutritional specifications due to improved management.

                      equation describing the relationship illustrated in Figure 11 is
 The mathematical equation describing the relationship illustrated in Figure 11 is shown
 shown below. This may be applied aid an assign assign relative nutritional values
 below. This may be applied as an as to aid to relative nutritional values to managerial
 decisions impacting live body weight body weight and FCR. Note data
 to managerial decisions impacting liveand FCR. Note data applicable to 500 g through
 2,800 grams 500 g through 2,800 grams live bird weight.
 applicable to live bird weight.

 Cumulative feed conversion ratio
 CD1 = 7017.65491 + (1.3773 _ BWT) – (0.00009006 _ + (5.247565*10-8*BWT3) –
 CD1= 7017.65491 + (1.3773*BWT) – (9.006*10-5*BWT2)BWT2) + ((5.247565 _ 10-8) _
 BWT3) – (5200.87308 (1566.92696*CFCR2) – _ CFCR2) – (0.75909 _
 (5200.87308*CFCR) + _ CFCR) + (1566.92696(0.75909*(BWT*CFCR)) (BWT _
 [P < .0001; R2 = 0.9391]
 [P < .0001; R2 = .9391]
 Daily feed conversion ratio3
 Daily feed conversion ratio3
 CD = 4180.202 + (1.667*BWT) – (2.9675*10-4*BWT2) + (1.359715*10 -7*BWT3) –
 CD = 4180.202 + (1.667 _ BWT) – (0.00029675 _ BWT2) + ((1.359715
 (1408.89875*DFCR) + (272.21113*DFCR2) – (0.37068*(BWT*DFCR)) _ 10-7) _
 BWT3) – (1408.89875 _ DFCR) + (272.21113 _ DFCR2) – (0.37068 _ (BWT _ DFCR))
 [P < .0001; R2 = 0.8834]
 [P < .0001; R2 = .8834]
  CD=caloric density (kcal MEn/kg diet)
  BWT=body density (kcal/kg
 1CD=caloric weight (g)

 2BWT=body weight (g) not shown
  Graphical representation
 3Graphical representation not shown
 McKinney and Teeter, OSU
 McKinney and Teeter, OSU
 By inserting values into the equation with and without the managerial decision, one may
 estimate the “nutritional change” that would be benefited by the response as the
 difference between the two values.

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                          Broiler Nutrition Guide

The Figure 11 equation may also be rearranged to predict FCR for a field production scenario
under a presumed “near ideal” standardized environment. This will provide an FCR indicator
of combined differences existing between the field feed evaluation matrix and the generalized
stress consequence encountered, versus the standardized production environment.

FCR = 24.152 + 2.3700*10-4*BWT -7.65*10-8*BWT2 + 2.91*10-11*BWT3 -0.014*CD + 2.26* 10-6*CD2

Generally the predicted standardized FCR value will be lower than the observed field estimate.
For example, under standardized conditions a cumulative FCR of 1.61 was obtained for broilers
reared to 2.36 kg on a diet with 3250 kcal of MEn/kg ration. Conversely, under an applied field
application with the same caloric density and different environment, broilers were observed to
have an FCR of 1.84. If the formulization matrixes are similar then, from a nutritional vantage,
the FCR discrepancy reflects environmental differences. By employing the caloric density
equation from figure 11 the costs may be further quantified as caloric value. In this case an
effective dietary caloric density difference of 362 kcal MEn/kg exists. Further examination may
assist the producer by identifying areas whereby managerial input may enhance the production
environment and pay dividends. By examining performance measures in this manner, decisions
impacting production costs and output benefit, may be evaluated as a nutritional equivalence.

                       Figure 11. The Body Weight, FCR
                       and Caloric Density Relationship


    Weight (g)
                                                                       Caloric Density
                                                                     (kcal MEn/kg diet)

 Figure 11. Dietary caloric density (kcal MEn/kg diet), under defined conditions, may be
 expressed as the combination of body weight (g) and feed conversion, this may be
 utilized to build a data base of seasonal, managerial, feed milling and nutritional
 influences for decision making. McKinney and Teeter, OSU

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                         Broiler Nutrition Guide

    5. Optimizing the Performance Environment
Providing satisfactory environmental conditions will enable the broiler to achieve the best
possible performance. Poultry performance has the potential to be maximized when the
overall production environment is also optimized. Stress consequences can begin in the
hatchery and/or hatchery to farm transport with consequences that far exceed the original
stress duration period. Growth, feed conversion, disease susceptibility and processing plant
condemnations may all be compromised because of problems stemming from the hatchery
and/or subsequent transport to rearing facilities. Personnel must work at every phase of bird
handling and rearing to minimize perturbations that negatively impact bird health and well
being. Only in this manner can the genetic potential of today’s poultry be approached.

                              Nonpathogenic Stress
A nonpathogenic stressor is defined as any environmentally based insult necessitating
physiological response to sustain homeostasis. Such stresses may include ambient
temperature, the gaseous atmosphere (ammonia, relative humidity, oxygen at a minimum),
feed and water availability, noise, lighting and interactions of these with other variables.
                                     Air Quality
Air naturally contains nitrogen (78.1%), oxygen (20.9%), argon (0.93%), carbon dioxide
(0.03%) and various trace elements (0.01%) at sea level. However, in the normal production
processes concentrations of these components vary considerably. Though poultry have the
ability to contend with a broad range of gaseous conditions they are particularly susceptible
to low oxygen content, by-products of heating systems and gaseous production products
originating from the litter. As altitude increases oxygen becomes a limiting nutrient for all
livestock classes. Birds exposed to poor air quality can exhibit reduced performance.

A study exposed day-old chicks to various atmospheric oxygen concentrations (8.60, 12.60,
16.60, 20.60%) for 8 hours simulating inappropriate transport stress. Study results indicated
that short term oxygen deprivation impacts both subsequent growth rate and ascites risk.
Mean growth rate declined incrementally as atmospheric oxygen declined. Contrasting the
two lowest oxygen levels with the two highest resulted in reduced (P=.03) 42 day growth
rates (by 7 points). Ascites incidence significantly rose (P=.055) from 2.48 to 4.5% at 42
days of age.
                               Ambient Temperature
Since homeothermy is only achieved after chicks generally reach a week of age, stress
consequences for the first week differ from later periods. Any time ambient temperature
exceeds the birds TN zone; heat production, and consequently oxygen consumption, are
elevated. This occurs because the bird must expend energy to generate heat, if cold, or to
dissipate heat if too hot. Young broilers are most susceptible to cold stress as they have a
higher surface area per unit weight. Increased susceptibility to heat stress occurs in older
birds because the surface area available for heat dissipation is reduced. The projected
thermoneutral midpoint temperature, for full fed broilers, declines from a 32.2 C at hatching
to approximately 22 C for a 2.5 Kg bird. These numbers are influenced by a variety of factors
including body composition, altitude, ventilation rate (air velocity), ration consumption and
composition as well as relative humidity.

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                        Broiler Nutrition Guide

Any time the bird is exposed to ambient temperature deviations from the thermoneutral
zone, management and housing alterations should be considered. Failure to do so will
force the bird to adjust, and such adjustments are usually at the expense of feed
conversion and/or growth rate. Figure 13 illustrates the caloric cost on bird maintenance
needs that can be associated with ambient temperature deviations from the birds zone of

                Figure 12. Projected Zone of Thermoneutrality
                       for broilers to 2.25 kg. mass

           32                                     TN Temperature
           30                                     Linear (TN Temperature)

                 0         0.5           1          1.5           2           2.5
                                     Body Weight (kg)
 Figure 12. Estimated thermoneutral ambient temperatures (TN) for birds to 2.5 kg
 body weight housed at 40-70% relative humidity under minimized stress conditions.

 TN (C) = 31.896 - (4.625*BWT) Beker and Teeter, OSU

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                                      Broiler Nutrition Guide

                                                           Figure 13.

                                 Temperature Elevation                Temperature Reduction
                             Total Fed HP @ TN                    Total Fed HP @ TN
     Daily HP (kcal)

                             Maintentance HP @ TN                 Maintentance HP @ TN
                             Maintentance HP @ TN + 2.5C          Maintentance HP @ TN - 2.5C
                             Maintentance HP @ TN + 5C            Maintentance HP @ TN - 5C



                             7      14      21     35       42    7      14      21      35     42
                                     Age (Days)                            Age (Days)
  Figure 13. Caloric expenditure of male-full fed-broilers and birds maintained at body
  weight homeostasis while housed at their projected TN midpoint, note that exposing
  birds to either a 2.5 and 5 C AT change, elevates maintenance energy cost, diverting
  energy away from production. Beker and Teeter OSU.

Lighting programs have been reported to impact growth rate, feed conversion and ascites
susceptibility. When considering a lighting program it is important to provide ample time,
during lighting periods, to enable the flock to react. For example, changing lighting in
increments that are too short would not allow enough time for all birds to consume feed and
water. Lighting impacts feed efficiency, when sufficient time is allowed for adequate feed
consumption, primarily by reducing maintenance energy needs.

                                                     Feed Form
Broiler rations must be fortified with the correct amounts of energy and nutrients. The
physical form of the diet, however, must also be considered and should not be viewed disjoint
from nutrient specifications as both impact ration value. Diet physical form can vary from
mash to pelleted or extruded forms. In some cases these products may be mixed with
various amounts of whole grain just prior to feeding. Beneficial aspects of further processing
rations include both managerial and bird benefits. On the management side feed handling
characteristics are improved. On the bird side, improvements in growth rate and/or feed
conversion have been noted. Though many companies further process their feeds, what is
actually delivered to the bird may well be a varying mixture of fines, pellets and/or crumbles.
Only the physical form of the ration placed in front of the bird for consumption will have the
opportunity to impact performance. A decline in the integrity of the processed form
proportion almost always occurs in the handling-transport-storage-delivery processes.

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                                         Broiler Nutrition Guide

If pellet or crumble durability is low, then the amount of fines increases and the further
processing value decreases. Figure 14 displays the potential impact of pellet quality on the
energy sparing value as caloric density. This relationship may be applied to assign value to
further processing itself and / or the overall consequence of feed handling. In those situations
whereby a producer may desire to slow growth by reducing dietary caloric density of the diet,
physical form of the ration offered should also be considered as an option.

                          225                                       Figure 14. Physical form of
                                                                    rations presented to broilers
  Kcal MEn Per Kg Diet1

                                                                    has an impact upon the
                                                                    diet’s calorific value. Energy
    Energy Sparing

                          150                                       sparing responses to 20%
                                                                    pellets appear to be feed
                                                                    consumption mediated, while
                                                                    responses between 60-80%
                                                                    appear to be activity related.
                           75                                       The equation may be applied
                                                                    to estimate calorific value of
                                                                    processing or consequence
                                                                    of handling mediated feed
                            0                                       form degradation.
                                0   20    40   60   80        100
                                    Diet Pellet Percentage
  PQ caloric value (kcal MEn/kg ration) = 1480.202 + (1.16673*BWT) - (2.9675 x 10 -4
 *BWT2) + (1.359715*10 -7*BWT3) - (1408.89875*DFCR) + (272.21113*DFCR2) -
 (0.37068*BWT*DFCR); R2 = 0.88, P < .01; Mckinney and Teeter, OSU
 BWT = body weight (g)
 DCFR = daily feed conversion ratio

Independent of pathological disease, the bird is impacted by its hygienic environment.
Though it would be simpler to view broilers as independently functioning entities, they
compete with numerous microorganisms found within the body and immediate environment.
Specific microbial affects may be either beneficial (vitamin synthesis, toxin destruction etc.)
or detrimental (toxin production, infection, nutrient destruction, immunological based energy
wasting). Birds reared in germ free environments have been reported to have as much as
a 15% overall elevation of energetic efficiency. Reducing the birds’ microbial load has the
potential to enhance growth rate, feed conversion, dressing percentage and elevate breast
yield as well as reduce consequence any physiologic stress where improved energetic
efficiency is a potential therapeutic (heat stress, ascites). Under practical conditions, caloric
value of nonpathogenic hygiene management ranges from 50 to 200 Kcal/kg diet.

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                          Broiler Nutrition Guide

                              6. Feed Conversion
Feed conversion, the compilation of feed consumption divided by live bird weight, is an
important aspect of overall performance. For this calculation the initial weight of the chick is
usually ignored, while more precise measures would subtract that mass and report feed per
unit gain (Figure 15). Nonetheless, the feed to body weight ratio is influenced by a plethora
of interacting components. Major determinants of FCR include bird age-body size,
environment, appetite, management and ration form-composition among others (Figure 16).
As birds age their feed conversion ratio increases due to increasing maintenance cost, and
the increasing proportion of gain accrued as lipid. Therefore, younger birds will have a better
FCR than older, and the FCR for “starter, grower and finisher” periods will be significantly
influenced by bird ages. Since FCR is a weight ratio, unadjusted for water content, birds
synthesizing lean will have a better FCR, as lean mass is 75.4% water and lipid mass is just
9%. Birds accruing lipid, however, will still have a positive FCR as it represents mass
accretion for a feed input. Important aspects of ration composition relate to the efficiency of
substrate utilization for tissue synthesis and the composition of tissues being synthesized.
Though feed and energetic efficiency are correlated, the fact that water and mass, in lieu of
energy, are included in the determinations can make the values less meaningful.

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                      Broiler Nutrition Guide

                                                            Figure 15.
           Figure 15. Cumulative and Daily                  The relationship between
           FCR Versus MEn Consumption                       feed conversion, expressed
FCR                                                         on a daily basis (yellow)
3.0                                                         and on a cumulative
                                                            basis (green) versus
                                                            energy     consumption.
2.6                                                         Note as the bird matures
2.4                                                         that the amount of feed
2.2                                                         required to achieve a
2.0                                                         unit of gain increases
1.8                                                         markedly for the daily
1.6                                                         value and in a buffered
                                                            fashion       for      the
1.4                                                         cumulative value. These
1.2                                                         values are interactively
1.0                                                         impacted by managerial
                                                            and ration composition
      0                 10000                      20000    decisions. Beker and
                    ME n Consumption (kcal)                 Teeter, OSU.

                        Figure 16. Daily Feed
                    Consumption Versus Day of Age
     Daily Feed
  Consumption (g)
             0        10        20            30       40     50          60
Figure 16. Daily feed consumption increases with age. Optimization of production-
management will help to maximize conversion of consumed feed into body mass. Often
birds with the best FCR consume the same amount of feed as the poor converters,
however, they gain more body weight. Beker and Teeter, OSU

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                           Broiler Nutrition Guide

   7. Growth as Proportion of Mass Versus Yield
The concept of growth and yield may be examined in several ways. Growth as grams of
mass is straight forward and easy to measure; however, yield is often viewed as a
percentage and can be misleading. When tissue growth is viewed as mass, output is a
straight forward and quantitative measure that serves well to guide the production process.
When yield is the criteria of growth and viewed as a percentage of overall products,
misconceptions may arise. For example, a nutritional change intended to manipulate a
specific output may only alter the mass of another component. As a result, this could have
the appearance of impacting the intended result in a manner that did not increase mass
output. Consequence here would be unrealized tissue output with a potentially needless
dietary cost elevation. This is illustrated by feeding elevated concentrations of dietary protein
to enhance breast or lean yield. Increasing protein consumption may indeed increase the
proportion of breast meat and lean tissue in the carcass. This elevation may however be due
to the fact that the efficiency of lipogenesis, via dietary protein, is less than that for
carbohydrate or lipid. Consequently, the enhanced percentage of breast and/or lean may
only reflect a reduced carcass fat mass. If that is the desired result, it is usually more cost
effective to simply lower a ration’s caloric density. Feeding elevated dietary crude protein
levels, also has the impact of reducing metabolic efficiency. And, under stressed conditions,
feeding excess dietary protein has the potential to elevate the incidence of metabolic
disease. Yield is best viewed as mass, especially when coupled with the efficiency of
metabolizable energy use for overall gain.

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                          Broiler Nutrition Guide

       8. Nutrient and Energy Recommendations
Since feed expenditures frequently comprise the largest component of bird production cost,
decisions regarding ration composition have a significant impact upon profitability. However,
ration composition is just one of the many interactive components that must be met for
efficient production. Any management, housing, environmental or hygienic inadequacy can
reduce bird performance. Indeed, interactivity between nutrition and the aforementioned
variables is illustrated by the caloric values placed upon feed form, lighting, ambient
temperature and hygiene among others. Managerial decisions that impact bird energy
expenditure have the impact of effectively altering dietary calorie/nutrient ratio. The astute
poultry grower will combine managerial, environmental and dietary interactivity to produce
the most efficient bird possible. The principle goal of dietary guidelines is to provide
acceptable combinations of energy + dispensable nutrients along with the complete array of
indispensable nutrients enabling the broiler to reach its genetic potential.

                          Basic Nutrient Relationships
The overall broiler production objective is the creation of lean tissue with acceptable lipid
content. Production efficiency is the balance of appetite driven feed inputs with wastage
outputs. Portions of the wastage points, such as maintenance energy expenditures under
thermoneutral conditions, are obligatory. In contrast, other portions of energy expenditure
are determined by the birds’ environment and producer managerial decisions. Aside from
expenditures for maintenance and activity, the cost of lean tissue accretion is relatively
constant for a reasonably fed and housed bird. Variations in production efficiency
measures, excluding low feedstuff quality and obligatory cost, are usually associated with
maintenance variables and rations with divergent calorie/protein ratio via their impact upon
energy metabolism. The role of the nutritionist is to examine such interactions and
prescribe feedstuff-nutrient combinations to optimize the performance characteristics
chosen by the company.

The performance characteristics chosen for optimization vary considerably among
companies, and as discussed in the following sections, have a marked impact upon ration
formulization goals. Performance objectives can range from body weight and feed
conversion, to breast yield or even survivability under stressed conditions. Once these are
chosen then the measures for success may be created. The best data source for nutritional
modifications is feedback from the overall production system. This feedback should include
not only live performance and survivability data, but also accurate carcass compositional
information from the processing plant. Combined with the stated company objectives, this
information guides the formulization decisions to make the best diets possible.

Bird energy needs may be expressed in numerous ways. Historically, the metabolizable
energy (ME) system has been the most widely developed and applied. As a result, bird
nutrient requirements are usually qualified as pertaining to a diet of stated MEn or in a
ratio to MEn. As the ME system does not account for heat losses, any variability in heat
production will result in varying nutrient/energy ratios at the cellular level. Ideally, a
coupling of bird energy expenditure with indispensable requirement would guide the
formulization process. However, with the current system nutritionist are forced to rely on
production system feedback as their benchmark for environmental and managerial
                                             23                                        COBB
                                Broiler Nutrition Guide

influences upon ration utilization. Calorific values of aforementioned managerial-
environmental influences should help to fine tune the nutritional-managerial interface.

Aside from direct energy expenditures, nutrients in excess of that utilized for lean accretion
will be converted to lipid. Substrate use for lipid synthesis varies and can have a direct
impact upon feed conversion, carcass composition, dressing percentage and apparent
breast yield. For example, estimates suggest that it will take 3.1 g dietary protein, 2.3 g
dietary carbohydrate and 1.2 g dietary lipid to synthesize just 1 gram of body fat. This makes
the pattern of dispensable nutrients used as energy sources have a significant influence
upon final carcass composition and feed conversion.
Though nutrient requirements are traditionally expressed in phases, this is more a matter of
milling and feed handling constraints than of truly segmented nutrient needs. For example,
the protein requirement for a ration containing 3,200 kcal MEn/kg, is 23% for a 1-21 day old
chick, 20% for 21-42 days and 18% for 42 to 56 days (NRC, 1994). Bird nutrient needs do
not change abruptly on these specified days, but rather they change continuously over time.
Therefore, the time frame can have a significant influence on the estimated requirement. As
many companies feed at periods differing from classical recommendations, alternative
expressions of requirements are needed. However, cautions are warranted: if producers
initially feed exactly at the bird’s requirement, before long they are feeding above the bird’s
need and expensive nutrients are wasted. Conversely, if birds are fed below their nutrient
requirement till they “grow into” the ration, then rations are deficient for a period of time
(Figure 17) and performance can wane. In either case, neither feed nor energetic efficiency
is optimized.

                                                                  Figure 17. The impact of
          Figure 17. Nutrient Intake vs. Broiler Age phase feeding broilers
                                                                  potentially results in
                                                                  periods of either over or
                                                                  under feeding growth
                                          Underfeeding            determining (rate limiting)
                                                                  nutrients (Corzo and
    Nutrient Intake

                                          Overfeeding             Teeter, OSU).

                        Theoretical Nutrient

                      Starter    Grower      Finisher

                                Broiler Age

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                           Broiler Nutrition Guide

                                      Protein Needs
Considerable information exists regarding protein requirements. Data suggests that once
the dietary protein requirement-amino acid needs are reached, that minimal additional
enhancement in carcass protein occurs with further fortification. In addition, it is observed
that a reduction in dietary protein (within reason and with indispensable amino acids
maintained) has minimal impact on overall growth and final carcass protein yield. Exceptions
to these general tendencies include the subtle enhancement of breast yield with fortification
of some indispensable amino acids and the enhancement of bird appetite and with subtle
dietary protein reduction. Therein lies a portion of the art of nutrition, with the greater
appetite one may attain a larger bird with a subtle protein deficiency. Conversely, fortification
of some amino acids in a ration that has satisfied the “protein requirement” may result in
greater yield of desired parts. For companies simply monitoring live body weight, the
motivation to feed reduced protein diets is clear. However, specific amino acid fortification
within an adequate protein level may potentially result in better breast yield. Indeed, the
company feeding the reduced protein level, depending upon feed intake, may get as much
breast (on gram basis), but at a reduced percentage as the birds contain more carcass fat.

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                            Broiler Nutrition Guide

  9. Feeding For Yield and Lean Meat Production
Within a satisfactory production environment, carcass and lean-breast mass may be
enhanced via nutrition. To effectively utilize nutrition to enhance production, it is
advantageous to simultaneously lower the diversion of feed nutrients to body homeostasis-
immunological response via housing and management. Reducing a diversion of feed
nutrients can have the same impact on carcass composition as diet modification.
Conversely, failure in this area can also negate expensive dietary changes. Once a
satisfactory environment for the intended growth is prepared, then nutrient specifications
may be optimally modified to impact carcass yield and lean meat proportions. Making subtle
changes in the ratios of various essential amino acids to energy and dietary crude protein
levels can indeed impact final carcass characteristics and proportional masses. It is
beneficial to attain data from the processing plant such that the overall picture (carcass mass
and proportions) may be continually monitored and seasonal strategies evolved. In this
manner one can avoid the illusion of elevated lean proportions simply at the expense of
metabolic efficiency and carcass fat.

For optimization of lean mass, all indispensable as well dispensable nutrients plus energy
must be at the accretion location simultaneously. Any deficiency of nutrients required in the
synthesis-maintenance of lean tissues will result in a reduced final lean mass. This also
dictates a reduced proportion of lean mass if lipid synthesis is maintained or elevated.
Fortunately, the combined ration-bird metabolic characteristic does not necessitate that we
continuously monitor all 40+ nutrients. In most situations it is sufficient to identify the 3-4 rate
limiting nutrients in each nutrient category for monitoring. Insuring that the rate limiting
nutrients are contained along with sufficient energy supply will create the opportunity for
efficient lean accretion.

Formulating diets to supply specified levels of the most common rate limiting amino acids
(lysine, methionine, threonine, arginine, tryptophan), within a fixed level of dietary crude
protein, is usually sufficient to maintain generalized lean accretion. The critical amino acids
are determined by feed ingredient composition and amino acid bioavailability. In typical
grain-soybean based diets the bird may, assuming adequacy of the housing environment,
deposit lean tissue in response to increasing the levels of lysine. Others have suggested
that an increase in the levels of sulphur amino acids (methionine and cystine) is correlated
to a reduction in fat deposition. However, these are not disjoint processes and should not be
viewed as such. In order to obtain maximum meat yield with minimum carcass fat levels both
lysine and sulphur amino acid levels must be simultaneously optimized. Other essential
amino acids, along with the substrates utilized for lipogenesis (protein, lipid, carbohydrate,
dispensable amino acid) also play a role in this highly interactive area. It is important to
remember that, although fat can be regarded as a waste product, a minimum level of carcass
fat is required to prevent the meat becoming dry and tasteless when cooked.

                     Optimizing the Nutritional Approach
Phase feeding conventional rations typically results in under and over consumption of
nutrients during the early and latter periods of the phase interval, respectively. Ideally,
a more refined working model would guide the formulization processes. It is possible;
using qualitative on-farm feed blending techniques, to match the ration composition with
the birds’ daily nutrient requirements. Though such blending is not generally available,

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                          Broiler Nutrition Guide

a working model is desirable for company analysis of feeding intervals. Today,
considerable variation exists between company feeding interval variation and the
composition of interval rations.

Description of daily nutrient and energy needs, as defined by the environment-managerial
interface, is mathematically possible. These can be used in turn coupled with bird production
data to best evolve ration formulization standards. As far as protein nutrition is concerned,
more is not always better, and less is not always worse. Nutritional balance in relationship
to daily need and dietary energy is the objective. The following equations and tables provide
examples of estimates, under a low stress environment, for daily energy, crude protein and
lysine allowances to support lean tissue accretion of the Cobb broiler.

                      Apparent Crude Protein Maximum
Maximum may be an incorrect use of the term, as successful boiler production can occur
with greater amounts of protein consumption than indicated here. However, research has
found through experimenting with various ration types a set of daily quantitative intake
values, beyond which further consumption does not generally elevate protein accretion. In
these studies levels of critical amino acids were fixed with the only variable being crude
protein primarily in the form of dispensable amino acids. Dietary crude protein consumption,
independent of critical indispensable amino acids, is listed in Table 2 and predicted by
equations 1-8.

EQUATION 1: Predictive equation for cumulative protein intake based upon day of age.
Limitations of this approach are failure of the production environment to produce a growth
curve match to the one utilized. In most feeding situations this would result in an
overestimation of protein need.
Highest crude protein need with satisfactory indispensable amino acids
= 1.97747 + 1.60348*day + 0.55084*day2 - 2.51236*10-3*day3;
As an example, the total protein consumption for 15 and 35 day old birds
would be about 141 and 625 grams, respectively.

One may also utilize this equation to estimate the quantity of protein needed for any
production interval as follows: Where B (dayb) is the day farthest along the growth curve
and A (daya) is the earliest day. Similar to equation 1, accuracy here is determined by the
production growth curve matching the standard. With this assumption, the approach
enables determination of maximal protein need with respect to the desired time interval
(Equation 2).

EQUATION 2: Estimation of protein need for a specified time interval.
Initial day = Intdaya
Final day = Intdayb
Protein needed for the interval
= (1.97747 + 1.60348*Intdayb + 0.55084*Intdayb2 - 2.51236*10-3*Intdayb3
-(1.97747 + 1.60348*Intdaya + 0.55084*Intdaya2 - 2.51236*10-3*Intdayb3
As an example, the total protein consumption for birds 15 and 35 days of age would be
about 484 grams.

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                          Broiler Nutrition Guide

EQUATION 3: Alternatively, bird protein need may also be related to body weight.
The advantage here is that the necessity for the production growth curve to match the
standard is reduced.
Prediction of cumulative protein consumption need (g) based on body weight (g).
= -15.8598 + 0.28746*BWT + 3.9642*10-5*BWT2 - 1.736*10-9*BWT3
As an example, the total protein consumed for birds weighing between 508 or 814
grams would be 140 or 626 grams, respectively.

EQUATION 4: Alternatively, bird protein need may also be determined for a body weight
differential. In the following example, the first body weight is bwta and the second bwtb.
Similar to the cumulative equation above, the advantage for the technique is the reduced
necessity for the production and standard growth curves to match.
Dbwta = Initial body weight (g)
Dbwtb = Final body weight (g)
Protein consumption for body weight interval.
= (-15.8598 + 0.28746*Dbwtb + 3.9642*10-5*Dbwtb2 - 1.736*10-9*Dbwtb3)
 -(-15.8598 + 0.28746*Dbwta + 3.9642*10-5*Dbwtb2 - 1.736*10-9*Dbwta3)
As an example, the total protein consumed for birds weighing between 508 and 1814
grams would be 486 grams.

                  Feeding Reduced Crude Protein Rations
Excess broiler protein consumption serves essentially no benefit. The added nutrient may
elevate ration cost, and it will reduce metabolic efficiency. The average conversion efficiency
of amino acid energy into lipid is just 45% (including cost of nitrogen metabolism), while the
efficiency for absorbed carbohydrate and lipid is estimated at 78% and 84%, respectfully. As
discussed, any elevation in carcass yield by feeding excessive protein may well be via
reduced energetic efficiency and hence lowered carcass fat. Consequently, the most cost
effective ration in terms of MEn calories consumed will be the one with sufficient, not
excessive protein content. Studies have been conducted to examine the extent to which
crude protein may be reduced. In these studies levels of critical amino acids were fixed with
the primary variable being reduced crude protein mostly in the form of dispensable amino
acids. Reduced dietary crude protein consumption, independent of critical indispensable
amino acids, is also listed in Table 2 and predicted by equation 5-6.
EQUATION 5: Predictive equation for cumulative protein intake based upon day of age.
Limitations of this approach are failure of the production environment to produce a growth
curve match to the one utilized. In most feeding situations this would result in an
overestimation of protein need.
Reduced crude protein need with satisfactory indispensable amino acids
= 0.40025 + (1.18418*day) + (0.50083*day2) - (1.955947*10-3*day3)
As an example, the total protein consumption for 15 or 35 day old birds would be about
124 and 572 grams, respectively.

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                           Broiler Nutrition Guide

One may also utilize this equation to estimate the quantity of protein needed for any
production interval as follows: Where B (dayb) is the day farthest along the growth curve
and A (daya) is the earliest day. Similar to equation 5, accuracy is determined by the
production growth curve matching the standard. With this assumption, the approach enables
determination of maximal protein need with respect to the desired time interval (Equation 6).

EQUATION 6: Reduced protein need for a specified time interval.
Initial day = Intdaya
Final day = Intdayb
Protein needed for the interval
= (0.40025 + (1.18418*Intdayb) + (0.50083*Intdayb2) - (1.955947*10-3*Intdayb3))
- (0.40025 + (1.18418*Intdaya) + (0.50083*Intdaya2) - (1.955947*10-3*Intdaya3))
As an example, the total protein consumed for birds between 15 and 35 days of age would
be about 447 grams.

EQUATION 7: Alternatively, reduced bird protein need may also be related to body weight.
The advantage here is that the necessity for the production growth curve to match the
standard is reduced.
Reduced cumulative protein consumption need based on body weight (g)
= -16.73268 + 0.25588*BWT + 4.001*10-5*BWT2 -1.21809*10-9*BWT3
As an example, the total protein consumed for birds weighing 508 or 814 grams would be
about 123 or 572 grams, respectively.

EQUATION 8: Alternatively, reduced bird protein need may also be determined for a body
weight differential. In the following example, the first body weight is bwta and the second bwtb.
Similar to the cumulative equation above, the advantage for the technique is the reduced
necessity for the production and standard growth curves to match.
Dbwta = Initial body weight (g)
Dbwtb = Final body weight (g)
Protein consumption for body weight interval
=(-16.73268 + 0.25588*Dbwtb + 4.001*10-5*Dbwtb2 -1.21809*10-9*Dbwtb3
-(-16.73268 + 0.25588*Dbwta + 4.001*10-5*Dbwta2 -1.21809*10-9*Dbwta3)
As an example, the total protein consumed for birds weighing between 508 and 1814
grams would be about 449 grams.

                         Summary Broiler Protein Need
Ultimately, there are an assortment of factors that will influence decisions regarding protein
levels that are fed. Paramount among these is the optimization of conversion efficiency and
production of a finished product that is of uniform quality. Under practical feeding situations,
the need for dispensable and some indispensable amino acids may be reduced as long as
the specified critical 4 amino acids are maintained. This occurs without apparent loss of lean
accretion potential. Requirement estimates are provided in Table 2.

                                              29                                          COBB
                         Broiler Nutrition Guide

Companies must use sound decision making in the utilization of recommended dietary
guidelines, as ultimately the optimal ration form will be determined by the environment-
managerial decision-nutrition interface. The calorific value of such managerial effects as
lighting program, feed form, hygiene level, ambient temperature and feedstuff matrix
assignment will each impact the final result. Indeed, the quantitative value placed upon
feedstuff energy value is also a variable that makes recommendations qualitative. The MEn
value for a given feedstuff can range considerably from one source to another. Despite these
constraints, however, coupling the principles expressed in these writings with end product
(bird carcass composition) feedback should provide the poultry producer with sufficient
information to make sound decisions and enable successful poultry performance within the
regional constraints encountered.

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                           Broiler Nutrition Guide

Table 2. Energy and protein needs to 55 days of age.

 Day of   Body     Feed Daily    Energy     High         Daily     Reduced      Reduced
 Age      Weight   Intake Feed   Intake     Protein      Protein   Protein      Daily Protein
          (g)      (g)    (g)    (kcal Men) Intake (g)   (g)       Intake (g)   Intake (g)
  1       59       18      10     56         4           4.1         2          2.3
  2       73       33      14     100        8           3.2         5          3.3
  3       95       51      19     156        12          4.3         8          4.2
  4       113      74      23     226        17          5.4         13         5.2
  5       141      101     27     309        23          6.4         19         6.1
  6       168      133     32     406        31          7.4         25         7.0
  7       195      169     36     515        39          8.4         33         7.9
  8       227      209     40     638        48          9.4         41         8.8
  9       259      254     45     774        58          10.4        50         9.7
  10      295      303     49     924        70          11.4        61         10.6
  11      331      356     53     1,087      82          12.3        72         11.5
  12      372      414     58     1,264      95          13.3        83         12.3
  13      417      477     62     1,454      110         14.2        96         13.2
  14      463      543     67     1,657      125         15.1        110        14.0
  15      508      614     71     1,874      141         16.0        124        14.9
  16      558      690     75     2,104      159         16.9        140        15.7
  17      612      770     80     2,348      177         17.7        156        16.5
  18      667      854     84     2,605      196         18.6        173        17.3
  19      721      943     89     2,875      217         19.4        190        18.1
  20      780      1,036   93     3,159      238         20.2        209        18.8
  21      844      1,133   97     3,456      261         21.0        228        19.6
  22      903      1,235   102    3,776      281         21.8        248        20.3
  23      971      1,341   106    4,110      302         22.6        269        21.1
  24      1,034    1,451   110    4,458      324         23.3        290        21.8
  25      1,102    1,566   115    4,819      347         24.1        312        22.5
  26      1,170    1,685   119    5,193      371         24.8        335        23.2
  27      1,238    1,808   123    5,581      396         25.5        359        23.9
  28      1,311    1,935   127    5,982      421         26.2        383        24.6
  29      1,379    2,067   131    6,396      447         26.9        408        25.3
  30      1,452    2,202   136    6,823      474         27.5        434        25.9
  31      1,524    2,342   140    7,263      502         28.2        460        26.6
  32      1,588    2,485   144    7,716      531         28.8        487        27.2
  33      1,669    2,633   148    8,181      561         29.4        515        27.8
  34      1,742    2,785   152    8,659      591         30.1        543        28.4
  35      1,814    2,940   156    9,149      622         30.6        571        29.0
  36      1,891    3,100   159    9,651      654         31.2        601        29.6
  37      1,964    3,263   163    10,166     687         31.8        631        30.2
  38      2,041    3,430   167    10,692     720         32.3        661        30.7
  39      2,118    3,601   171    11,230     754         32.8        692        31.3
  40      2,191    3,775   174    11,779     789         33.4        724        31.8
  41      2,268    3,953   178    12,340     825         33.9        756        32.3
  42      2,345    4,135   182    12,912     861         34.3        789        32.8
  43      2,422    4,320   185    13,504     894         34.8        822        33.3
  44      2,504    4,509   188    14,107     928         35.3        856        33.8
  45      2,581    4,700   192    14,721     963         35.7        890        34.3
  46      2,658    4,896   195    15,346     998         36.1        924        34.7
  47      2,740    5,094   198    15,980     1,034       36.5        959        35.2
  48      2,817    5,295   201    16,625     1,070       36.9        995        35.6
  49      2,898    5,500   204    17,279     1,107       37.3        1,031      36.0
  50      2,976    5,707   207    17,943     1,144       37.7        1,067      36.4
  51      3,057    5,918   210    18,616     1,182       38.0        1,104      36.8
  52      3,134    6,131   213    19,298     1,220       38.3        1,141      37.2
  53      3,216    6,347   216    19,989     1,259       38.7        1,179      37.6
  54      3,293    6,565   219    20,689     1,298       39.0        1,217      37.9
  55      3,375    6,786   221    21,396     1,338       39.3        1,255      38.3

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                 10. Vitamins and Trace Elements
The vitamin and trace element requirements for various ages of broiler are now defined. To
ensure that adequate amounts are provided, diets must be supplemented according to both
the level and availability of the vitamin and trace element in the various feed ingredients.

Table 3. Recommended supplementary levels of vitamins and trace elements (per
tonne of feed)1

                                      Starter           Grower             Finisher

  Vitamin A               (MIU)       12.0               10.0               9.0
  Vitamin D3              (MIU)       4                  4                  3
  Vitamin E               (KIU)       30                 30                 30
  Vitamin K (a)           (g)         4                  3                  3
  Vitamin B1 (thiamin)    (g)         4                  2                  2
  Vitamin B2 Riboflavin   (g)         9                  8                  8
  Vitamin B6 Pyidoxine    (g)         4                  4                  3
  Vitamin B12             (mg)        20                 15                 15
  Biotin                  (mg)        150                120                120
  Choline                 (g)         400                350                300
  Folic Acid              (g)         1.5                1.0                1.0
  Nicotinic Acid          (g)         60                 50                 50
  Pantothenic Acid        (g)         15                 12                 12
  Manganese               (g)         120                120                120
  Zinc                    (g)         100                100                100
  Iron                    (g)         40                 40                 40
  Copper                  (g)         20                 20                 20
  Iodine                  (g)         1.0                1.0                1.0
  Selenium                (g)         0.30               0.30               0.30

 Successful production has been observed with these values, however numerous factors
such as feed processing, bird stress, feedstuffs used among others impact the required level.
Optimum profitability should also be considered.

                          Recommended Nutrient Levels
The following nutrient specifications are intended to provide information that will contribute
to the optimization of performance, under a diverse array of production situations (Table 4).
These tables should be used as a guide of the general nutrient requirements of broilers
grown to 55 days of age or less. The specifications are for chickens reared in temperate
climates under good conditions. Various discussions contained in this manual provide
general information for conditions that deviate from the norm. When the mean diurnal
temperature exceeds this range, or insufficient oxygen consumption occurs, the birds’
nutrient requirements change and modifications should be made. Additional specifications
have been provided for free range chicken production.

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Table 4. Recommended Broiler Nutrient Specifications
in Finished Feeds
                                       Starter        Grower    Finisher 1   Finisher 2

                                       A/H            A/H       A/H          A/H
  Protein                  (%)         21.5           19.5      18.0         17.0
  Lysine-total             (%)         1.33           1.25      1.10         1.04
  Lysine-digestible        (%)         1.17           1.10      0.97         0.91
  Methionine-total         (%)         0.56           0.53      0.48         0.44
  Methionine-digestible    (%)         0.50           0.48      0.43         0.40
  M+C-total                (%)         0.98           0.96      0.88         0.80
  M+C-digestible           (%)         0.86           0.84      0.77         0.70
  Tryptophan               (%)         0.21           0.19      0.17         0.16
  Threonine                (%)         0.85           0.80      0.73         0.70
  Arginine                 (%)         1.39           1.30      1.20         1.11
  Calcium                  (%)         0.90           0.88      0.84         0.78
  Available Phosphorus     (%)         0.45           0.42      0.40         0.35
  Sodium                   (%)         0.20           0.17      0.16         0.16
  Chloride                 (%)         0.20           0.20      0.20         0.20
  Potassium                (%)         0.65           0.65      0.65         0.65
  Acid: Base balance       meq/100g    20             20        20           20
  Linoleic Acid            (%)         1.25           1.25      1.25         1.25
  Energy                   (MJ/kg)     12.65          13.25     13.40        13.40
                           (Kcal/kg)   3023           3166      3202         3202
                           (Kcal/lb)   1374           1439      1455         1455
  Feeding Programs         (g/bird)    500            1400      2800         to marketing

                          Free Range Chicken Production
The Cobb broiler can be successfully grown under an extensive range of production
systems. Free range chickens are invariably grown at a slower rate than intensively reared
stock in order to produce meat with a more mature flavor. They require specialized diets,
which may be based entirely on vegetable ingredients, and are often reared using controlled
feeding management techniques. The following nutrient specifications have been devised
with the aim of producing males and females aged 56 days, weighing 2.8kg and 2.3kg
respectively. Feed control may be necessary, depending on the specific conditions in which
the birds are grown.

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                           Broiler Nutrition Guide

Table 5. Nutrient Specification for free range broilers
                                        Starter        Grower       Finisher 1     Finisher 2

  Protein                  (%)          21              19          18             17.5
  Lysine-total             (%)          1.15            1.09        1.04           0.93
  Lysine-digestible        (%)          1.01            0.95        0.92           0.82
  Methionine-total         (%)          0.48            0.46        0.49           0.44
  Methionine-digestible    (%)          0.42            0.40        0.43           0.39
  M+C-total                (%)          0.86            0.82        0.87           0.78
  M+C-digestible           (%)          0.76            0.83        0.76           0.69
  Tryptophan               (%)          0.18            0.18        0.19           0.17
  Threonine                (%)          0.76            0.74        0.72           0.65
  Leucine                  (%)          1.23            1.19        1.17           1.05
  Iso-leucine              (%)          0.76            0.73        0.71           0.64
  Valine                   (%)          0.87            0.84        0.83           0.74
  Arginine                 (%)          1.21            1.14        1.15           1.02
  Calcium                  (%)          0.90            0.90        0.90           0.90
  Available Phosphorus     (%)          0.45            0.45        0.45           0.45
  Sodium                   (%)          0.18            0.17        0.16           0.16
  Chloride                 (%)          0.20            0.20        0.20           0.20
  Potassium                (%)          0.65            0.65        0.65           0.65
  Acid: Base balance       meq/100g     20              20          20             20
  Linoleic Acid            (%)          1.25            1.25        1.10           1.10
  Energy                   (MJ/kg)      11.50           12.00       12.50          13.00
                           (kcal/kg)    2747            2866        2986           3105
  Feeding Programs         (g/bird)     500             1000        to marketing

                                 Yellow Skinned Birds
The Cobb broiler is a naturally yellow skinned bird, but eliminating all the sources of pigment
from its feed will produce a white skinned, white fleshed chicken. In regions of the world
where wheat is the staple cereal, consumer preference tends to be for a white fleshed
product. In regions of the world where maize (corn) is the staple cereal consumer preference
frequently slants towards a yellow skinned product. In order to produce yellow skinned
broilers, the birds have to be fed a diet that includes pigments. These pigments may be either
xanthophylls that occur naturally as a component of some feedstuffs or they may be added
as a feed supplement. The intensity of the yellow color in the bird products depends entirely
on the amount of pigment included in the diet and deposited in the flesh. Natural materials
(e.g., corn, corn gluten meal, dehydrated alfalfa, grass meal, lucerne meal) can be used to
produce birds with pigmented flesh, but the result is often variable. The reason for this
variability is the natural variation in the level of pigmenting xanthophylls and their pigmenting
potency in the feed raw materials. To achieve a uniform color it is usually necessary to
supplement the natural xanthophylls with extracted or synthetic pigments.

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                             11. Feed Manufacture
                                 Raw Material Quality
Correct nutritional specifications are an essential pre-requisite for any diet. However, it must
be recognized that the quality of the diet is entirely dependent on the quality of the raw
materials. Textbook feeding values for raw materials are only a guide to the actual
contribution that a particular ingredient may make to the final diet. For major raw materials it
is essential to monitor their actual composition. The quality of the diet is affected by:

    • total nutrient level and availability of essential nutrients;
    • metabolizable (MEn) or true metabolizable energy (TME);
    • the proportion of saturated to unsaturated fats for starter diets (due to the limited
      ability of chicks to digest saturated fats);
    • anti-nutritional factors, e.g., histamines (biogenic amines) in fish meal,
      trypsin inhibitors in field beans;
    • toxins, e.g., mycotoxins produced in the field (ergot and fusarium in
      wheat) or in storage (aflatoxin);
    • the addition of enzymes to improve the digestibility of wheat or other
      raw materials;
    • the development of novel raw materials, e.g., processed vegetable
      protein products or new varieties of cereals with characteristics intended
      to make them especially suitable for feed manufacture.

\                                      Feed Hygiene
Feed may be contaminated by a number of disease organisms, but those of primary
concern are Salmonella and Campylobacter because of their importance to human
health concerns. It is widely recognized that feed plays an important role in the spread
of such organisms throughout the chicken industry. To achieve the objective of
minimally contaminated broiler feed, a number of important steps must be taken. All
incoming raw materials should be selected on the basis of routine bacteriological
monitoring. This involves regular sampling based on the volume and frequency with
which each material is purchased. Storage warehouses and dock discharge facilities
should be periodically inspected to ensure that adequate attention is paid to vermin
control. The construction and management of the feed mill should be designed to
ensure that there is no possibility of cross contamination from untreated materials.
Feed processing lines should be discrete and the flow of product should always run to
minimize final product contamination. The mill facilities must be clean. Subjecting the
mixed raw materials to high temperatures by using specialized milling equipment such
as expanders, extruders and conditioners contributes significantly to a reduction in
bacterial contamination. The degree of bacterial kill is dependent on a combination of
temperature, moisture and time. Total bacterial elimination is achievable, but it may be
at the expense of important macro and micro nutrient availability. Recontamination of
heat treated feed must be prevented. The critical mill area is post pelleting. The hot
pellets should be cooled as rapidly as possible by blowing only clean, filtered, cold air
through the stream of product. Condensation in this area should be eliminated, since
it provides an environment that will allow bacteria to survive and multiply. Organic
acids and for maldehyde can be used to help control the growth of bacteria and
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molds in both raw materials and finished feed. They are an important tool in the mill hygiene
programs, but the critical areas for bacteria contamination control are heating and cooling.
Feed delivery vehicles are also an important link in the chain of bio-security. It is an
advantage to use vehicles specifically dedicated to the delivery of feed, rather than general-
purpose haulers or farm vehicles. All vehicles must be regularly and thoroughly cleaned,
both inside and outside, including in particular the discharge system.
                                       Fat Quality
Neo-natal chicks are not capable of digesting saturated fats properly, so the fat in the starter
feed should be largely unsaturated (e.g., soybean oil). The ability of chickens to metabolize
fats improves as they develop, so the grower and finisher diets can be formulated to include
increasing amounts of saturated fat (e.g., palm oil, and tallow).

Fats, particularly long chain unsaturated fats, are damaged by heating and oxidation. Fat
blends often include waste products from commercial frying operations and the by-products
from chemical processes, such as distillation residues from oil refining. Fats such as these
will reduce growth rate and may have an adverse effect on the health of the birds as well as
their carcass quality. The use of anti-oxidants in the fat and feed can have an important
mitigating effect on fat quality.
                                    Protein Quality
Soybean meal is the major protein source used in broiler feed and it can, and does vary
considerably in nutrient content. The causes of this variation are diverse: the soybean crop
nutrient profile may vary in quality from year to year and area to area; products with the same
nominal specification will vary in their nutrient content depending on the manufacturing
conditions used to cook the meal and extract the oil. Cooking is an especially important
process because it is necessary to heat the beans to destroy an anti-nutritive factor called
Trypsin Inhibitor (TI). TI lowers the digestibility of the total protein fraction of the feed and
impairs the growth rate of the chickens. Under cooking leads to poor protein digestion due
to the TI, whereas over cooking causes both the protein and fat in the meal to be extensively
denatured and potentially reduces their digestibility. Regular monitoring of either TI or urease
activity is very important. Samples of every new intake of each soybean product should be
subject to colorimetric comparison with previous batches and random samples should be
sent for chemical analysis. Acceptable urease values, using the colorimetric test, fall
between 0.05-0.20.

Fishmeal can be included in broiler starter diets to provide a good source of digestible amino
acids. Fishmeal also contributes Omega-3 PUFAs, organic selenium and other valuable
nutrients, but as with soybean meal, either over or under cooking will reduce its nutritional
value. Regular quality control is very important. The levels of available lysine, salt, minerals
and oil stability should all be monitored.

Cereals not only contribute a large proportion of the energy to a broiler ration, but they
also provide approximately 30% of the crude protein. A change in the level of crude protein
in feed wheat from 11.5% to 10.5% can reduce the crude protein level in the finished feed
by up to 2-3% points. The quality of cereals clearly needs to be regularly monitored. In the
case of feed wheat, starch and available starch levels will change with conditions during
growing and harvest. Although not directly correlated to energy or protein availability, the
higher levels of non-starch polysaccharides (NSP) often found in wheat indicate that the
energy values may be reduced. The use of xylanase enzymes to break down the non-starch

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                          Broiler Nutrition Guide

molecules is now common practice in all major wheat using countries. Periodic assessment
of the nutritional value of wheat should be undertaken, as wheat variety, harvest conditions
and xylanase enzyme activity can vary, leading to differences in available levels of protein
and energy.
                    Micro-nutrient and Medicinal Inclusions
The importance of controlling and monitoring the use of feed additives, particularly vitamins
and anticoccidials is all too frequently understated. Vitamins and trace elements are involved
in all the metabolic processes of the body and, while deficiency symptoms are rarely seen
today, sub-optimal performance caused by a marginal deficiency in just one of these
nutrients is not uncommon. Anticoccidials and other medicinal products must be
incorporated in feed at the correct levels to ensure their efficacy.

Table 6. Assessing Broiler Feed Analysis
  Nutrient               Normal Range              Analytical precision   Additional Information
                         (depending on
                         nutrient specification
  Protein                17-24%                    98%                    A test of quantity
                                                                          not quality
  Oil/Method A           8-10%                     92%                    Ether extract method
  Oil/Method B           8-10%                     92%                    Acid hydrolysis (e.g. for
                                                                          phospholipids) values
                                                                          higher by 0.7%-0.8%.
                                                                          Test enables energy
                                                                          value to be calculated
  Starch                 35-45%                    98%                    Necessary for energy
  Sugar (sucrose)        3-6%                      95%                    Necessary to calculate
                                                                          energy content of feed
  Manganese              100-150 mg/kg             95%                    Inexpensive method of
                                                                          assessing vitamin/trace
                                                                          element supplement
                                                                          inclusion, since base
                                                                          levels are 15-20 mg/kg
                                                                          and supplement levels
                                                                          80-100 mg/kg
  Calcium                0.85-1.15%                95%                    Errors may be high due
                                                                          to separation. Pelleting
                                                                          reduces separation.
  Phosphorus             0.65-0.75%                95%                    Availability is
                                                                          approximately (total %)
                                                                          60-65% of total.
  Vitamins               A-10 - 14 iu/g            95%                    Vitamin analysis
                         E-40 - 150 iu/g           95%                    expensive. Vitamin A is
                                                                          easiest to assess and
                                                                          may be used to indicate
                                                                          correct supplement levels.

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                            12. Feed Management
                      Raw Materials Quality and Testing
Ensuring that broiler feeds will successfully meet nutrient specifications begins with the
assurance that the raw ingredient composition matrix is accurate. The matrix must reflect
the actual nutrient content of an ingredient for energy, protein, essential amino acids,
minerals, vitamins and trace element content. Only then may the ingredients be accurately
selected and formulated to provide the correct levels of nutrients to be contained in the
broiler feed. In this regard, the feed is only as good as the raw materials themselves, they
must meet specification and our knowledge of their composition must be complete. Many
nutritional problems arise due to lack of attention to the quality of raw materials used to
prepare the desired rations. Ensuring the quality of the finished feed involves attention to the
detail of raw material nutrient composition, freedom from toxic factors as mycotoxins,
bacterial contamination, biogenic amines and rancid fat as well as quality feed formulation,
manufacture, delivery, farm storage and presentation to the bird. Accurate testing of raw
materials and finished feed allows quality control to close the loop.
                                      Feed Testing
Good feed sampling technique is as important as good laboratory practice if the results of
the analysis are to reflect the real nutrient content of the feed. The majority of variation
between the results of the same analysis from two different samples of the same feed,
analyzed at the same laboratory, is likely due to poor sampling technique. The sample must
be representative of the feed from which it was taken, and this cannot be achieved by
“grabbing” a sample of feed from the feed trough. A 20 ton bulk load of finished feed will be
made up from a number of different mixed batches of raw materials. It is unlikely that these
batches will be identical in composition, so to get a representative sample of feed it is
necessary to take a number of sub-samples and combine them to make a composite
sample. Take at least 5 sub-samples from any size of load. These sub-samples should be
combined to form a composite sample for analysis. Always record details of the date, the
location at which the sample was taken, the feed type, and the batch number. Make sure that
the laboratory understands which tests are required and where the results should be sent.

                                Whole Wheat Feeding
Whole wheat feeding is undertaken in a number of countries. The benefits include a
reduction in feed manufacturing cost, reported improvements in gizzard development and
the efficiency of digestion. Feeding whole wheat also provides the ability to manipulate
nutrient intake. The disadvantages may be poorer uniformity, lower growth rates and a
reduction in lean meat yield, as well as a potential loss of bio-security. Wheat can be
added either at the point of dispatch from the feed mill, or the point of feeding. Adding
the wheat at the point of feeding is technically preferable, but a feed proportioning
system is essential if the technique is to be successful. The cereal is added to the feed
in quantities ranging from 5-30%, starting usually from 4-7 days of age. The overall
usage of wheat is 10-12% of the total volume of feed consumed. Whole cereals other
than wheat may be used, but grains as large as maize (corn) must be milled before
they are presented to the birds. When wheat feeding is undertaken it is important to
take account of the dilution effect on the nutrient specification of the whole feed
presented to the birds. In par ticular, it is essential to ensure that medicines
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                         Broiler Nutrition Guide

such as cocciostats are fed at the correct levels. The successful use of controlled feeding
techniques requires a significant management input. The birds should be regularly weighed
and adjustments to the feeding program may be necessary. Feeding to meet daily nutrient
requirements can be a useful technique and has been shown to have benefits, but it relies
on the nutrient levels in the finished feed meeting their expected values.

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                        13. Physiological Stress
Two types of physiologic stress, high ambient temperature-relative humidity combinations
and inadequate atmospheric oxygen, center on metabolic perturbations with overlapping
therapeutics. In the case of heat stress, birds are compromised from waste heat production.
In the case of ascites, oxygen needs exceed the bird’s ability to consume. In both situations,
improving energetic efficiency and/or slowing growth can assist with survival.

                     Heat Stress (HS)/ General Concerns
Mean diurnal temperature has a significant effect on the physiology of broiler chickens and
will affect their agricultural performance. The thermoneutral comfort zone for poultry declines
from 32 C at hatching to 24 C at 5 weeks of age. When ambient temperature rises and
necessitates heat dissipation via evaporative cooling, elevated humidity makes panting
inefficient and further elevates bird heat production. The birds’ thermoneutral comfort zone,
with regard to humidity, lies between 50% and 70% relative humidity (RH). When the RH
rises from 70% to 95%, at a constant temperature, feed intake, growth rate and survivability
may decline. Optimizing broiler production during heat stress necessitates that the
appropriate combination of nutritional and management therapies be applied.

Heavier birds generally have more of a problem with heat stress since they have less surface
area for heat dissipation per unit weight. In temperate regions hot weather may cause heat
stress (acute heat exposure) when a period of high temperatures coincides with a flock
nearing slaughter age. These conditions are sporadic and unpredictable, making
therapeutics difficult. In hot regions of the world the problem is more of chronic exposure to
high mean diurnal temperature. In such situations the birds will somewhat adapt to the high
temperature in which they are kept, though performance is generally less.

Studies indicate that birds exposed to heat stress retain the potential for enhanced growth
rate. If feed intake is elevated during the stress bout, or once the ambient temperature has
fallen, bird growth rate will increase. Several management options are available to elevate
feed consumption during heat stress, but to do so without impacting heat dissipation
capacity, potentially elevates mortality. This is important because it demonstrates that
successful manipulation of energy consumption will improve growth rate, but it also
demonstrates that increased energy consumption can be devastating during survival limiting
heat stress. Producers need to decide how much emphasis to place on growth during the
stress event. Allowing, or encouraging growth to slow during the highest temperature period
of the day may be desirable if survivability becomes an issue. During the cooler portions of
the day compensatory growth may help to offset losses.

Physiologically, the heat stress dilemma is an issue of energy balance. Thermobalance is a
composite of heat production and its dissipation. Of the two heat dissipation routes
(evaporative and nonevaporative), the potential for nonevaporative heat loss is reduced as
ambient temperature increases above TN. Consequently, for the heat stressed broiler to
avoid overheating it must increasingly rely on respiration rate mediated evaporative cooling
and/or reduced feed consumption. Nonevaporative cooling is the most energetically efficient
means to dissipate heat and its optimization will enhance feed conversion efficiency. By
optimizing ventilation the poultry manager can enhance nonevaporative cooling and thereby
aid heat dissipation most efficiently. In summer stress periods ventilation is critical during

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                          Broiler Nutrition Guide

the day, however, it also has a marked impact during the evening hours by removing waste
heat as quickly as possible and ensuring maximal time for compensatory growth.

HS/Evaporative Cooling:
Evaporative cooling usually becomes the principle heat dissipation route during heat stress.
Though the bird can dramatically increase evaporative cooling by increasing respiration rate,
the efficiency of this process is variable. As the relative humidity rises, both the extent and
ease with which the bird can support evaporative cooling declines. These relationships must
be considered for optimal management of ventilation and in-house evaporative coolers such
as foggers and cooling cells.

HS/Heat Production:
Broiler heat production averages approximately 45% of MEn consumption. Ambient
temperatures at, or below, the thermoneutral zone, have no adverse heat production
consequence other than wasted nutrients. Under heat stress conditions however, bird heat
production has consequences. Birds lower heat production by consuming less feed and
slowing growth rate. Feed conversion efficiency also deteriorates as feed consumption
declines. Management decisions must keep these factors in mind.

HS/Management Options:
In order to achieve consistent performance it is important to maintain feed consumption and
nutrient intake. The importance of adequate poultry housing can not be overemphasized
and should be the focal point of an effective heat stress management program. The greatest
proportion of economic loss associated with heat stress is usually the result of lowered feed
intake, though mortality can be excessive. While the heat stressed bird increases its growth
rate as feed consumption increases, and the potential for a near normal growth rate is still
present, elevating feed consumption without impacting heat dissipation capacity can
increase mortality. Caution must therefore be utilized in management decisions directed
towards manipulating feed and energy intake, and in fact, they should be coupled with heat
dissipation management.

Several options exist for enhancing feed and energy consumption of heat stressed broilers.
It is important to utilize lighting to the fullest extent possible without limiting time for
consumption due to lighting program. Continuous lighting or 23 hours light:1 dark should be
considered. Anything that draws the birds’ attention to the feed, such as running automatic
feeders or physically shaking feeders will elevate consumption. Feed forms as pelleted and
extruded products enhance the feed density and generally elicit a greater consumption
during heat stress. Other avenues of enhancing density, such as improved feed digestibility
and increasing nutrient density help to maintain consumption. Fat addition to the diet
increases nutrient density and enhances growth under high ambient temperature conditions.
Using more fat not only improves palatability but reduces heat production per calorie
consumed. However, with fat and with the other techniques discussed, it is critical to realize
that if successful, heat production will likely become elevated. This is also true for the
inclusion of fat as it tends to enhance consumption more than it’s heat increment reduction.
Dietary caloric value may also be increased with pellet quality.

In hot conditions it may be beneficial to feed the birds only during the coolest part of the day
and night. Removing feed and fasting chicks reduces the birds’ heat load. Under acute high
ambient temperature-relative humidity stress this management tool can increase survival.
However, at least 3 hours is required for the feed to clear the digestive tract and reduce
                                              41                                         COBB
                          Broiler Nutrition Guide

metabolism so one must plan ahead as removing feed after the onset of heat stress is of little
value. Fasting birds for 3 hours prior to heat stress initiation, coupled with a 6 hour heat
stress period, can increases the time without feed to 9 hours. This does reduce time
available for consumption and fasting, during cool time periods will reduce growth rate.
Consequently, this management avenue should be used only when mortality risk is high. It
is important to provide enough feeder space so that birds do not become overexcited and
bruise or scratch themselves during the early re-feeding phase. When properly applied,
evidence suggests that compensatory gain during the evening hours will offset reduced
gains during the day.

HS/Water Management:
Water consumption by the heat stressed bird is a critical consideration as over 80% of their
heat production is dissipated via evaporative cooling. A supply of cool water must be
available at all times. Reducing water temperature from 30.0°C to 12.4°C has been shown
to lower body temperature by as much as 0.5°C with minimal impact upon water intake. If
the litter can tolerate added urinary output, encouraging water consumption by adding
NaHCO3, NaCl or KCl may have benefits as evaporative heat dissipation extent and
calories dissipated per breath are correlated with water intake. Birds in positive water
balance are better able to maintain body temperature homeostasis and performance.

HS/Other Considerations:
Since feed consumption declines with heat stress, nutrient fortification should be considered.
The levels of supplemental vitamins and minerals in the feed should be adjusted to offset the
reduction in feed intake. Withdrawing the finisher period vitamin premix from heat stressed
broilers results in a greater performance reduction than withdrawing such premixes when
birds are housed within a thermoneutral environment.

Lowering the dietary protein, while maintaining essential amino acid fortification levels,
has been observed to improve bird growth rate and survivability. Indeed, such an
approach is one of the few observed to simultaneously improve both growth rate and
survivability. The crude protein levels must be adequate for anticipated growth, but they
should not be increased in line with the calculated decline in feed intake. Instead, the birds’
requirements for the essential amino acids lysine, methionine, arginine and threonine
should be met by forcing increased levels of synthetic amino acids into the feed
formulation. This will have the effect of satisfying the birds’ requirement for these nutrients
without increasing their heat burden.

Optimizing the bird’s hygienic environment has the potential to improve heat stress
performance since the gastrointestinal tract represents a significant source of metabolic
heat. Lowered heat production, with reduced microbial loads, occurs due to reduced
gastrointestinal tract mass and reduced immune challenge. Such broilers have been
observed to produce less heat (~7%; Table 1) and consume less oxygen per calorie of
metabolizable energy consumed.

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Ascites is commonly known to poultry producers as waterbelly, altitude disease or avian
edema. Ascites is the result of a physiologic syndrome of multiple causes and generally
attributable to insufficient oxygen consumption. Historically, ascites was viewed as being a
high altitude disease with its occurrence being more common in countries where regions
containing poultry production exceeded 1,500m. However, combinations of disease, toxins
and/or insufficient management and/or nutrition can either interfere with chick ability to
consume oxygen or elevate its requirement to the point that ascites can occur at virtually all
altitudes. When oxygen consumption falls below metabolic need, compensatory physiologic-
cardiovascular alterations are made. These changes, however, are the triggers that send
this syndrome down a progressive path. Proper nutritional and environmental management
can do much to avoid the ascites issue.

The ascites syndrome in poultry is a clinical manifestation of oxygen insufficiency
precipitated by a divergent oxygen requirement and cardiovascular ability to supply it. Bird
oxygen need increases with tissue accretion rate and proportion as lean mass. Broilers
housed in metabolic chambers have been observed to consume 3.1 liters O2 per gram
protein gain vs. just 0.82 liters O2 per gram fat over a 35 day production period. As a result
one might conclude that various managerial and nutritional concepts presented to improve
FCR and/or cope with heat stress also have the potential to modulate ascites incidence.

Oxygen as a Nutrient:
All tissues are supported by an obligatory oxygen driven metabolism. Oxygen is required for
growth, maintenance and activity. Figure 18 partitions the cumulative oxygen consumption
profile for a growing broiler, under reasonable growing conditions, into its gross components.
The production of a 3.4 Kg broiler necessitates that the bird consume approximately 2,500
liters of oxygen during the production period. Of this 19% is utilized to support BMR, 36%
for a combined BMR, activity and waste energy associated with converting consumed MEn
into maintenance needs.

                   Figure 18. Partitioning of Oxygen          Figure 18.         Broiler total
                     Consumption vs. MEn Intake               oxygen consumption in liters
                                                              (green) partitioned into that
   O2 Consumption (L)
                                                              utilized to support gain (black)
       3000                                                   and       total    maintenance
                                                              need        partitioned     into
       2000                                                   BMR (red), BMR + lights
                                                              on activity      (blue) as well
                                                              as oxygen consumed to
                                                              support maintenance (yellow)
                                                              metabolism associated with
           0                                                  gain is displayed.        BMR,
                                                              activity and oxygen required
      -1000                                                   for the production process are
               0               10000                20000
                                                              nearly of equal magnitude.
                                                              Beker and Teeter, OSU
                          ME n Consumption (kcal)

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An evaluation of the 3 distinguishable expenditures for oxygen merit discussion as they offer
potential interaction via management and nutrition:

The activity components associated with maintenance, tissue gain and social behavior
warrant discussion. Ideally, for optimized utilization efficiency of both energy and oxygen, the
bird would have enough activity to acquire needed sustenance followed by reduced
locomotion expenditures. From a managerial perspective, proper administration of lighting
cycles and intensity has the potential to lower bird activity. Reduced day length and/or
lighting intensity is well documented to lower bird activity (see previous discussion). Fasted
birds housed under conditions of BMR elevate their oxygen consumption when the lights
come on. Reducing lighting intervals within the day provides broiler producers’ a means of
limiting activity that results in energy + oxygen expenditure. Consequently, it is of little
surprise that lighting program application enhances FCR and lowers mortality incidence.

Basal Metabolic Rate:
Previous discussion indicates that the amount of energy needed for maintenance can be
markedly elevated by ambient temperature. For example, a change in ambient temperature
of 5 C will elevate the maintenance oxygen needs by approximately 10%. Ambient
temperature, consequently, is a significant determinate of total bird oxygen need. Rearing
broilers within the TN zone will help to reduce ascites. Ambient temperatures deviating from
TN have the potential to elevate mortality at all altitudes, but are particularly detrimental at
elevations exceeding ~610 m or 2,000 feet.

Tissue Accretion and Needs Exceeding Maintenance:
The combination of management and ration balance continue to impact bird oxygen needs
once maintenance aspects have been addressed. Managerial decisions, independent of
ration composition, that worsen FCR will generally elevate the bird oxygen requirement and
ascites susceptibility. This is particularly true under conditions of AT deviation from TN and
elevated altitudes. Managerial decisions related to environmental definition (stocking
density, housing design, ventilation, brooder management, hygiene) have an increased
importance when dealing with the ascites issue.

Ration composition also influences bird oxygen need, especially when environmental
conditions fail to provide a reasonable growing condition. The combination of poor housing
environment and excess dietary crude protein can elevate ascites incidence. When dietary
protein is utilized as a source of energy, exceeding needs for lean tissue accretion, energetic
efficiency is lowered and more oxygen consumption is needed. As shown in Table 7, the
influence of caloric density and calorie protein ratio, though not as significant as altitude,
contribute to worsening the cardiovascular challenge. This is evidenced by blood hematocrit,
right ventricular mass and ascites heart ratio. Such occurrence is the result of the metabolic
efficiency for converting dietary protein MEn into lipid being just 45%. This is in contrast to
higher efficiencies for carbohydrate(78%) and lipid (84%). An additional consideration for
lipid is that it generally places the bird in a higher growth plane, further exacerbating oxygen
need. Lipid consumption will thereby not only elevate carcass fat but also oxygen need.
Therefore, a reasonable ration to minimize ascites is similar to one for minimizing mortality
due to heat stress perturbation, where added heat production via lipid and protein
exacerbate environmental consequence. Ultimately, the producer will need to decide
the ration composition warranted to cope with the specific environmental risk level
(determined by altitude, AT, brooder efficiency, ventilation, environmental toxins, etc).

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                                  HCT (%)                RV (g)                 AHR

     O2 (%)
          17                      38.25a                 0.42a                23.14a
         20.6                     32.62b                 0.40b                21.56b

     CD (kcal/kg)
         3200                     35.25                  0.40b                22.47
                                  35.62                  0.42a                22.23
            140                   36.26a                 0.42a                22.81a
                                  34.61b                 0.40b                21.88b

  Table 7. Altitude, caloric density (CD) and calorie-protein ratio (CPR) effects on
  hematocrit (HCT), right ventricular mass (RV) and ascites heart ratio (AHR=RV/total
  heart weight (g)/100) of chicks reared to 2 weeks of age. Vanhooser, Swartzlander,
  Beker & Teeter, OSU

Dietary Sodium
Excessive consumption of sodium, via the diet or from drinking water, places additional
stress upon the cardiovascular system. The combination of sodium source and
bioavailability can make sodium delivery to the bird uncertain. Often times, nutritionist
attempt to error on the side of feeding excessive sodium amounts so as to avoid the
possibility of deficiency. In the case of ascites, this approach can needlessly elevate ascites
risk. The bottom line is that serum sodium should not be allowed to exceed 155 meq. In
situations where ascites is a significant concern, attaining serum samples and testing for
serum sodium can provide information to see if Na is being over fortified.

Bird Ability to Consume Oxygen:
Altitude certainly plays a potential role in bird ability to consume oxygen. As elevation
increases the concentration of oxygen per liter air declines, and the effort expended to
consume it increases. In addition to altitude, other air quality and disease factors such as
ammonia, dust and respiratory infection are among the many contributing factors that have the
potential to lower bird ability to consume oxygen. Under generally good growing conditions,
with the exception of elevation, the altitude associated with physiological changes related to the
progressive ascites syndrome, appears to be approximately 1200 meters (Figure 19). It should
be noted, however, that this estimate is attained by using hematocrit, the earliest responding
component of the progressive array of cardiovascular changes associated with

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ascites development. Other criteria such as ascites score, right ventricular mass and ascites
heart ratio do not appear to change as early as hematocrit (Table 8). Nonetheless, diligence
is recommended for oxygen concentrations falling below ~19.4%. This corresponds to an
altitude of ~610 m or 2,000 feet. It is important to keep in mind that other environmental
factors such as ammonia, ambient temperature, stocking density, poor ration balance and
insufficient ventilation rate would be expected to impact such results. Unfortunately, these
factors result in physiologic adjustments occurring at lower altitudes.

                 Figure 19. Altitude Effects on Percent Blood Hematocrit
        Meters 0            1000           2000                3000           4000
          Feet 0            3280           6560                9840           13120
Vanhooser, Beker & Teeter, OSU

Table 8. Physiological Changes Under Varying Percent
Atmospheric Oxygen Percentage
       Variables         12              14                    16              18             20.6

       HCT (%)       48.92 ± 0.46a   42.24 ± 0.46b        35.77 ± 0.57c   32.60 ± 0.40d   31.88 ± 0.98d
       Ascore         3.00 ± 0.39a    2.23 ± 0.19b         0.67 ± 0.14c    0.38 ± 0.14c    0.25 ± 0.14c
       RV (g)         0.79 ± 0.04a    0.82 ± 0.04a        0.46 ± 0.03b     0.38 ± 0.03b    0.34 ± 0.08b
       AHR           52.36 ± 2.00a   43.37 ± 2.00b        24.00 ± 1.74c   22.91 ± 1.74c   20.99 ± 4.25c
       Means in a row with unlike superscript differ
  Hematocrit (HCT), ascites score (Ascore), right ventricular (RV) mass and ascites heart
  ratio (AHR=RV/total heart weight (g)/100) of broiler chicks reared to 14 days of age at
  varying atmospheric oxygen concentration. Vanhooser, Beker & Teeter, OSU

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Other Measures:
Once practical environmental and dietary management of ascites has been addressed, as
with heat stress survivability, one may choose to therapeutically slow growth. Slowing
growth reduces the overall need for birds to consume oxygen, thereby enabling the
growth-maintenance-bird ability to consume oxygen balance to normalize. Growth may be
slowed via utilization of feed restriction, reduced caloric density rations, mash diets and
lighting program.

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