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OCR for page 109
Poultry
INTRODUCTION
Environmental factors are generally recognized to have a major impact on
the production of meat and eggs from poultry. These include temperature,
humidity, light (length of day and intensity), altitude (air pressure and partial
pressures of oxygen and carbon dioxide), wind velocity (air movement), so-
lar energy, quality of air and water, and density of population. During the
last decade, the influence of environmental factors on poultry have received
greater attention so that more reliable baseline values are available. Most
studies have dealt with only one environmental factor with other factors
presumably held constant. Yet, we recognize that in husbandry practices, be
it in- or outdoors, poultry are subjected to a multiple of factors, none held
completely constant, and all interrelated. At times these factors could be re-
inforcing or counteracting the impact each has on the bird. Another compli-
cation, often ignored, has been the animal's acclimatization to environmental
forces that tend to allow poultry to withstand sudden short-term excursions
from the norm, which produce havoc to a nonacclimatized bird. A crucial
factor that appears to govern the TNZ and responses to hot or cold is acclima-
tion (Harrison and Biellier, 1969; Shannon and Brown, 1969; van Kampen,
1974; Waring and Brown, 19671.
POULTRY ENVIRONMENT
The use of shelter to shield poultry from the macroenvironment is an ap-
proach to enhance productivity and thus justify such expenditures. The struc
109
OCR for page 110
1 lo APPROCHES FOR PRACTICAL NUTRITIONAL MANAGEMENT
lure creates around the bird a meso- and microenvironment (Charles, 1974)
that moderates but does not alleviate environmental impact. In
temperature-nutrition studies, it~is important to consider the environment in
the cage (microenvironment) and to avoid use of measurements taken within
the building (mesoenvironment).
A "perfect" environment to the nutritionists for rearing poultry could be
defined as those ambient conditions that maximize gain in weight or egg out-
put with the least expenditure of nutrients. Unfortunately, the "perfect" en-
vironment may not be economically feasible. A compromise is reached, and
the direction of management is to achieve an "optimum" environment, one
in which the ambient situation is efficiently obtainable in terms of productiv-
ity and nutrient intake with a minimum of sacrifices. For example, if a low
ambient temperature reduces productivity, then supplying a mesoenviron-
ment at a higher temperature will be rewarding if the increased productivity
equals or exceeds the expenditure required to supply the higher ambient tem-
perature.
An example of such consideration is the evaluation of nutrient costs to
raise turkeys for maximum profits (Waibel, 1977~. When protein (soybean
meal) sources are relatively cheap, one apparently should feed the usually
recommended levels of protein to stimulate maximum gain in weight; but
when protein is expensive, the cost-accounting approach justifies lower
levels of dietary protein and less than maximum weight gain. And, to com-
plicate the situation, the ambient temperature at which the turkeys grow has
an impact on the profit-efficiency-weight gain output (Waibel, 1977~.
Although the final accounting for productivity is meat, eggs, and/or repro-
ductive output (young stock from hatching facilities), there are several in-
stances where environment affects nutrient utilization. Consider the discus-
sion on basal metabolism (page 274. A shift toward a higher environmental
temperature reduces energy expenditure of poultry (O'Neill et al, 1970;
Romijn and Vreugdenhil, 1969; van Kampen, 1974~. Thus, where higher
ambient temperatures are available birds expend less of their metabolizable
energy for maintaining a constant body temperature and appear to have the
option of shifting this savings of energy to production or improving feed effi-
ciency.
FEED INTAKE AND NUTRIENT REQUIREMENTS
At this point, a differentiation must be noted between the environmental ef-
fect on nutrient intake versus its effect on nutrient requirements. Inherent in
this recognition is that when nutrient intakes are altered by the environment,
an adverse effect on the animal should be alleviated by correspondingly ad-
justing dietary levels of the nutrients to compensate for altered daily intake.
If equal daily intakes of nutrients at different environmental conditions do
OCR for page 111
Poultry
111
not produce comparable productive outputs and/or efficiency, then we would
assume that the nutrient requirements were altered.
To illustrate this concept, consider the data in Figure 18 adapted from a
study by March and Biely (1972~. Chicks were reared at 20 and 31.1°C using
diets with graded levels of lysine covering the range from levels that are defi-
cient to those in excess. Two separate response lines were obtained when
feed intake was related to body weight gain in the two temperatures. The
slopes of the lines are nearly parallel, and the difference between the two
levels of intake indicates that chicks in the 31.1°C ambient temperature ate
about 20 percent less feed. Thus, the high temperature reduced feed intake
and consequently reduced gain. However, when the data are plotted on the
basis of lysine intake versus body weight gain, note that one response line
can describe the relationship despite the two environments (Figure 19~.
Thus, environmental effect on growth was not from a change in nutrient re-
quirements for growth, but instead was a consequence of an environmental
effect to reduce feed intake and thus lower the daily intake of lysine (and
other nutrients), which resulted in reduced growth rate. Note that at equal ly-
sine intakes, growth was comparable in both environments (Figure 19~.
In warmer environments, a decline in feed intake may or may not influ-
ence egg production or quality. How drastically feed intake is depressed and
for how long are what apparently determines the hen's response. Even in the
thermoneutral zone, a decline in feed intake of up to IS percent may not af
200
-
z 150 _
I
100 _
50 I/ 1 1 1 1
200
· = 20° C
= 3 1.1 C ,/
.
Y= -179 + 1.045 X /
,:
/ ·,
/
/ Y=-304+1.187X
250 300 350 400
FEED INTAKE (g)
FIGURE 18. Relationship between total feed intake and total weight
gain of White Leghorn chicks fed for IS days diets with lysine levels of
0.73, 0.88, 1.03, and 1.33 percent at two ambient temperatures (adapted
from data by March and Biely, 1972).
OCR for page 112
1 12 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT
300
-
~' 200
An
100
40--
Y = -5.43 + 42.1 X r = 0.98
it/ ~ = 20° C
` ~ = 31.1 C
1 1 1 1 1
2 3 4 5 6
LYSI NE I NTAKE FOR 1 5 DAYS (g/bird)
FIGURE 19. Relationship between accumulative intake of lysine and
accumulative growth of chicks reared at 20 or 31.1°C and fed diets for 15
days containing 0.73, 0.88, 1.03, or 1.33 percent lysine (adapted from
March and Biely, 1972).
feet production or quality of eggs (for reviews, see Polin and Wolford, 1972;
Snetsinger and Zimmerman, 1974) if the bird mobilized body reserves to re-
place the nutrient deficit (Davis et al., 1972; Polin and Wolford, 1972, 1973;
Snetsinger and Zimmerman, 19741.
In early studies, Wilson (1949) and Payne (1966) recognized that a drop in
egg production by chickens in hot environments was partially due to lower
energy intake. Recently, Dale and Fuller (1980) reported that high fat or high
fat-high density diets alleviate to some extent the weight loss of broilers at
31°C. Other studies, to be discussed, indicate that lesser amounts of feed
result in submarginal intakes of all nutrients and that their replacement does
not necessarily ensure a return to normal production. Warmer temperatures
reduce basal metabolic rate (Shannon and Brown, 1969) and maintenance
energy, the latter at an estimated 4 percent with each 1°C rise above thermo-
neutrality (Leeson et al., 19731. For example, White Leghorn and Rhode Is-
land Red hens at 33-34°C have a heat loss which is 58 and 51 percent, re-
spectively, of the values at 18.3°C (Ota and McNally, 1961). Part of the
decline is also accounted for by less activity to eat as extrapolated from
studies on laying hens restricted in feed intake (Jackson, 1972) or those more
efficient in feed utilization (Morrison and Leeson, 19781.
EFFICIENCY OF EGG PRODUCTION
The energetic equivalent of egg weight is generally accepted as 1.66 kcal per
gram of egg, including the shell. Recently, Sibbald (1979) related egg
OCR for page 113
Poultry
weight to caloric value by the equation:
Y = 19.7 + 1.81 X,
where
X - weight of egg (g),
Y = energy value (kcal/egg).
113
Egg shell is about 98 percent mineral and has a caloric value of about 0.24
kcal per gram (Bolton, 1958) or 1.2 kcal for a 5-g shell. Shell protein and
membranes account for almost all of this energy. The value of 1.66 is ob-
tained by combustion of an aliquot of blended egg in a bomb calorimeter
(Bolton, 1958) and is approximated from data presented by Cotterill et al.
(1977) showing that an average egg of 60.8 g contains 6.36 g of protein (5.7
kcal per gram of protein) and 6.52 g of lipid (9.4 kcal per gram of lipid) with
a caloric value of 96.9 kcal, which, added to the 1.2 kcal for shell, equals
98.1 kcal. (The yield of calories by combusting an egg is 37 percent from its
protein and 63.8 percent from its fat.) A flock laying at an average rate of 70
percent and producing eggs weighing an average 61 g is producing 42.7 g of
egg per bird per day, equivalent to 70.9 kcal. If these birds were consuming
each day l to g of feed containing 2.85 kcal of ME per gram, then the ener-
getic efficiency is 22.6 percent:
t70.9 kcal/~110 g feed x 2.85 kcal ME/g feed)] x 100 = 22.6 percent.
Tables 35 and 36 contain a series of values in which the energetic efficien-
cies are given for the range of egg weights from 50 to 65 g, a range of feed
intakes of 80 to 150 g per day, a range of egg production values of 60 to 75
percent, and, for two dietary levels of ME, 2.85 and 3.00 kcal/g. Therefore, a
decline or improvement in any of the above values, other than ME, as a result
of environmental factors, can be estimated from the change in energetic effi-
ciency of egg production obtained from the values in Table 35. If egg weight
remains constant at 65 g, egg production at 70 percent, and no change occurs
in body weight while feed intake declines from 110 to 100 g, then the caloric
efficiency has improved from 24.1 to 26.4 percent (Table 35), or an increase
of 9.5 percent.
A change in body weight complicates the situation. To consider the impact
of such an event, consider the following. Metabolizable energy values of
foodstuffs do not appear to be different for laying hens when in cold, warm,
or hot environments (Brown et al., 1967; Davis et al., 19721. Thus, the di-
gestive, absorptive, and excretion processes leading to retention of energy
from the diet were not affected in hens held at ambient temperatures ranging
from 7 to 35°C for as long as 6 weeks. Davis et al. (1972) noted that feed
intake was almost 26 percent less by the hens in the 35°C environment, but
OCR for page 114
114 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT
TABLE 35 The Efficiency of Converting Feed to Egg in Energetic
Equivalents, Assuming a Diet Containing ME = 2.85 kcal per g
Feed Intake (g/bird/day)
Average Egg
Weight (g) 80 90 100 110 120 130 140 150
60% egg production
50 21.8 19.4 17.5 15.9 14.6 13.4 12.5 11.6
55 24.0 21.4 19.2 17.5 16.0 14.8 13.7 12.8
60 26.2 23.3 21.0 19.1 17.5 16.1 15.0 14.0
65 28.4 25.2 22.7 20.7 18.9 17.5 16.2 15.1
05~/o eve Production
~7 ~
50 23.7 21.0 18.9 17.2 15.8 14.6 13.5 12.6
55 26.0 23.1 20.8 18.9 17.4 16.0 14.9 13.9
60 28.4 25.2 22.7 20.7 18.9 17.5 16.2 15.1
65 30.8 27.3 24.6 22.4 20.5 18.9 17.6 16.4
70% egg production
50 25.5 22.7 20.4 18.5 17.0 15.7 14.6 13.6
55 28.0 24.9 22.4 20.4 18.7 17.2 16.0 14.9
60 30.6 27.2 24.5 22.2 20.4 18.8 17.5 16.3
65 33.1 29.4 26.4 24.1 22.1 20.4 18.9 17.7
75~c egg production
50 27.3 24.3 21.8 19.9 18.2 16.8 15.6 14.6
55 30.0 26.7 24.0 21.8 20.0 18.5 17.2 16.0
60 32.8 29.1 26.2 23.8 21.8 20.2 18.7 17.5
65 35.5 31.5 28.4 25.8 23.7 21.8 20.3 18.9
they continued to lay at a high rate at the expense of body tissue stores. The
energy retention (metabolizable energy), which they determined to be 205
kcal per hen per day, was equivalent to 141 kcal per kg075 per day. Egg en-
ergy of 70.5 kcal per day was equivalent to 48.6 kcal per day per kg075,
yielding an energetic efficiency of 34.4 percent at 35°C. The hens weighed
only 1.55 kg at the end of 21 days, down from 1.83 at the start of the experi
O ~ _
meet. Using equations given by Davis et al. (1972) based on carcass anal-
yses, the energetic values of the hen's carcass contain 5,543 and 4,310 kcal
at the start and end of the experiment, respectively. The difference of 1,233
kcal for 280 g weight loss during 21 days yields a value of 4.41 kcal per
gram of body weight loss. The daily weight loss of 13.3 g, equivalent to
59.1 kcal (40.8 kcal per kg075), contributed to energy available to the hen.
Therefore, the calories available to the hens each day were the sum of metab-
olizable energy and that obtained from body tissues, a total value of 181.8
kcal per kg075. Egg energy was 26.7 percent of this total, as compared to
26.4 or 24.4 percent obtained in environments of ambient temperature and
OCR for page 115
Poultry
TABLE 36 The Efficiency of Converting Feed to Egg in Energetic
Equivalents, Assuming a Diet Containing ME = 3.00 kc al per g
Feed Intake (g/bird/day)
115
80 90 100 110 120 130
140
60~o egg production
50 20.8 18.4 16.6 15.1 13.8 12.8 11.9 11.1
55 22.8 20.3 18.3 16.6 15.2 14.0 13.0 12.2
60 24.9 22.1 19.9 18.1 16.6 15.3 14.2 13.3
65 26.9 24.0 21.6 19.6 18.0 16.6 15.4 14.4
65% egg production
50 22.5 20.0 18.0 16.3 15.0 13.8 12.8 12.0
55 24.7 22.0 19.8 18.0 16.5 15.2 14.1 13.2
60 27.0 24.0 21.6 19.6 18.0 16.6 15.4 14.4
65 29.2 26.0 23.4 21.3 19.5 18.0 16.7 15.6
70~o egg production
50 24.2 21.5 19.4 17.6 16.1 14.9 13.8 12.9
55 21.6 23.7 21.3 19.4 17.8 16.4 15.2 14.2
60 29.1 25.8 23.2 21.1 19.4 17.9 16.6 15.5
65 31.5 27.9 25.2 22.9 21.0 19.4 18.0 16.8
75% egg production
50 25.9 23.1 20.8 18.9 17.3 16.0 14.8 13.8
55 28.5 25.4 22.8 20.8 19.0 17.1 16.3 15.2
60 31.1 27.7 24.9 22.6 20.8 19.1 17.8 16.6
65 33.7 30.0 27.0 24.5 22.5 20.8 19.3 18.0
7°C, respectively. Therefore, the improved energetic efficiency of egg pro-
duction at 35°C, originally calculated as 34.4 percent, was only 26.7 percent
when the hen's bodily stores were included in the accounting. This example
illustrates two factors: (1) that temperature did not, per se, have an influence
on the partial efficiency of egg production and that (2) accounting only for
feed in the production of an egg can lead to misleading results as compared
to a more inclusive accounting of energy balance.
Other nutrients should be considered in their conversion to eggs and meat.
For example, hens at 100 percent production are estimated to be about 37
percent efficient in transferring protein from diet to amino acids in eggs (Cot-
terill et al., 19771. At 70 percent production the value is 25.9 percent. The
value 25.9 percent is derived from 1 10 g of feed at 15.5 percent crude pro-
tein, yielding 6.36 g of amino acids in the egg:
[6.36 g amino acids/110 g feed x 0.155 g cP/g feed)] x 100 = 37 percent,
37 percent x 0.7 production = 25.9 percent.
OCR for page 116
1 16 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT
In terms of dietary true protein (amino acids in feed), the efficiency value
would be higher because the level of true protein in feed is less than the
crude protein (nitrogen) level.
Referring again to data by Davis et al. (1972), the efficiency of amino
acid deposition into the egg appears to be enhanced by higher temperature.
This conclusion is arrived at by calculating the efficiency values of 29.6 and
40.6 percent at environmental temperatures of 7 to 10°C and 35°C, respec-
tively (Table 37~. In this experiment, body weight declined 235 g, with 9
percent, or 21.2 g, attributed to a loss of protein (Davis et al., 19721. The
daily loss of body protein averaged 0.5 g/day. This protein, if assumed to be
available for eggs, when added to the 11.2 g obtained from the diet, yielded
a total availability of 11.7 g/day. Based on this value, the efficiency of pro-
tein deposition into egg at 35°C was 40.3 percent, similar to values found
when the contribution of body protein was excluded. Unlike caloric effi-
ciency, which was corrected to a major extent upon accounting for body re-
serves, the efficiency for transfer of protein from diet to eggs appears to be
improved at warmer temperatures. Considerably more data are needed to
substantiate this conclusion, since it is possible that protein was utilized for
energy. If the latter is so, then feed formulation of energy to protein ratios
may have to be shifted upward in cold environments.
Another example for consideration is based on calculations from data by
Adams et al. (1962) and depicted in Figure 20. Clearly, two effects are
noted: one, which shows that feed intake of broiler-type chicks was reduced
at 31.2°C, and two, that high-energy diets reduced feed intake more than the
lower-energy diets fed at this high temperature.
Figure 21 reveals that gain in weight per unit of protein consumed versus
energy concentration in the diet is positively correlated and that this relation
TABLE 37 The Effect of Environmental Temperature on the Efficiency of
Protein Deposition in Chicken Eggsa
Egg Crude Amino
Environmental Mass Protein Acids
Temperature per Day Intake/Day per Egg Percent of Feed
( C) (g) (g) (g)b Protein in Egg
Expt. #1 10 45.9 16.8 4.82 28.7
Expt. #2 35 43.7 11.2 4.59 41.0
Expt. #3 7 49.7 17.2 5.22 30.4
Expt. #4 35 44.9 11.8 4.71 39.9
`' Derived from data of Davis et al., 1972.
h Amino acids comprise 10.5 percent of egg weight (Cotterill et al., 1977).
OCR for page 117
Poultry
2600
2400
LL
A
an
~ 2200
LL
LL
2000
1800 1 1 1 1 ~ 1 1
27nn
.
-
Y = 2264 + 0.048 x
-
-
-
-
-
Y = 3241 - 0.407 x
·= 21 1°c
is= 31.2°C
2900 3100 3300
METABOLIZABLE ENERGY OF DIET (kcal/g}
FIGURE 20. Relationship between dietary ME, feed intake, and ambient
temperature for broiler-type chicks 6-10 weeks of age (adapted from
Adams et al., 1962).
1.8
y 1.6
UJ
o
cr
-
z
~ 1.2
Y = -0.060 + 0.000483 X
Pooled
21.1°C 1
31 .2°C
1.0 L 1 1 1
2700
.
· = 21.1°C
a = 31.2°C
2900 3100 3300
METABOLIZABLE ENE RGY OF Dl ET (kcal/kg)
FIGURE 21. Relationship between gain, percent protein, and ME of the
diet fed to broiler-type chicks ~10 weeks of age (adapted from data by
Adams et al., 1962).
117
OCR for page 118
118
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OCR for page 119
Poultry
119
ship for growth seems to be unaffected by ambient temperature at 31.2°C
versus 21.1°C. Additional evidence indicating a lack of temperature influ-
ence on growth from protein is reported by March and Biely (1972), who fed
chicks diets deficient or adequate in lysine at 18.3, 22.2, or 29.4°C. The re-
sponse line is characteristic of lysine levels versus gain and is independent of
temperature. A review of data by McNaughton et al. (1978) on body weights
of broiler-type chicks at 4 weeks of age also reveals that at equal lysine in-
takes body weight was similar at 15.6 and 29.6°C (Table 38~.
FEED INTAKE
Estimations of the effect on feed intake of laying hens by temperature were
made by numerous investigators. Their data are given in Table 39, converted
to express the effect as a percentage change from controls kept at 18-25°C.
The variability is excessive for any definite mathematical equation to be es-
tablished. This should not be too surprising when one considers the heteroge-
neity of the factors, such as strain, length of time under heat stress, percent-
age production, weight of eggs, and ME values of the diet that existed among
these experiments. Obviously, one all-encompassing equation would appear
to be difficult to establish. However, within certain limits there is a possibil-
ity of obtaining a measure of feed intake related to temperature. These data
(Table 38) show a relationship of:
Y = 24.5 - 1.58 T.
where
T = ambient temperature (°C),
Y = percentage change of feed intake from controls in the thermo-
neutral zone.
This is a decline in feed intake of 1.58 percent per 1°C rise in temperature
referenced to the intake value at temperatures in the 18-25°C range. Payne
(1967) calculated for laying hens a decline in feed intake of 1.5 percent for
each 1°C rise in temperature through the range of 5 to 30°C. Emmans (1974)
calculated metabolizable energy on a daily basis to decline 4.3 kcal per 1°C
rise for white and brown egg layers. This value for a diet with metabolizable
energy of 2.9 kcal per gram represents 1.5 g of diet. Regression equations,
derived from data by Jones and Barnett (1974), reveal that turkey hens show
a decline in feed intake of 3.2 g or 1.5 percent for each 1°C rise between the
temperatures of 4.5 to 35°C. Thus, an overall estimate for relating feed in-
take to temperature change appears to be 1.5 percent/°C with 2~21°C as a
baseline.
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Representative terms from entire chapter:
egg production
124
4 - ~
.~ .o
._
Poultry
37.5
37.0
36.5
E 36.0
IL
in
A
c'
I
35.0
LL
U) _ _
34.5
34.0
33.5
33.0
/\
21° c
/
\
/ ~
~o°C
\
At/
1 1 1 1 1 1 1
\ 25°C
-
-
-
1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
CALCIUM INTAKE (g/bird/day)
FIGURE 23. The relationship between daily calcium intake and shell
thickness by turkeys fed 1.54, 2.01, or 2.48 percent dietary calcium at
each of four environmental temperatures (after Kohne and Jones, 1976).
125
climation occurred and egg production returned to near normal levels with
some improvement in shell quality, even though dietary nutrients were not
increased. In cyclic environments a return toward normal shell quality oc-
curred because a greater percentage of the eggs were laid after 0900 hours
(Miller and Sunde, 1975), an indication of a longer stay in the shell gland.
Despite the shell-less eggs and poor shell quality of hens in hot environ-
ments, bone mineralization remained at normal levels throughout.
ESTIMATING ME REQUIREMENT FOR LAYING HENS
Many equations are available to estimate the ME requirements of laying hens
exposed to different temperatures (for review, see McDonald, 1978~. Basi-
cally, such estimates depend on three factors: maintenance energy, energy
related to a change in body weight (energy is demanded for gain, energy is
126
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Poultry
127
released when weight is lost), and the energy for egg production. Thirteen
equations were recently presented (McDonald, 1978), along with the capa-
bility of each to predict the actual ME encountered from 16 published reports
from eight countries. None of the equations allows for an estimate of the en-
vironmental effect on maintenance requirements. Nevertheless McDonald's
equation predicted daily ME requirements within 1.6 percent of observed
values (Table 41~. Emmans (1974) derived equations to estimate ME require-
ments for light and mid-weight hens, and included a correction for tempera-
ture. In the assumption that the temperature at each of the areas in the pub-
lished report by McDonald was 21°C, Emmans' equation overestimates daily
ME by 18.5 percent (Table 40), and the overestimates increase as the as-
sumed temperature is raised. However, changing the equations by Emmans
to estimate maintenance energy based on W075 rather than W'° at 21°C im-
proves the overestimation down to only 3 percent (Table 404. Balnave et al.
(1978) estimates that maintenance energy for laying hens changes at the rate
of 1.4 percent per °C. Note that this value approximates the rate of change
(1.55 percent) obtained from the estimated effect of temperature on feed in-
take (Table 37~. Based on reviews by Grimbergen (1974) and Balnave
(1974), maintenance energy for light breeds is estimated to range between
126 and 135 kcal per W075 at 25°C. Grimbergen (1974) estimated poultry
generally need 113 kcal/W075/day for maintenance energy.
Combs (1968) predicted energy requirements for hens exposed to different
environmental temperatures as follows:
ME = (1.78 + 0.012 T)~1.45 W0653) + 3.13 /\W + 3.15 E,
where
ME = metabolizable energy (kcal/day),
T = environmental temperature (°C),
/`W = body weight (g),
W = body weight change (g), and
E = daily egg mass (g).
This equation does not account for differences in feather cover. To make
that correction the data by Emmans and Charles (1977) can be used. Their
estimate indicates that maintenance energy increases about 9 percent for each
unit increase of a score denoting loss of feathers; a score ranging from one to
SiX.
By assuming a correction of 1.5 percent per °C, compounded for mainte-
nance energy, an efficiency of 80 percent for energy to be converted into
weight gain or eggs, and calorigenic values of 4.4 kcal per gram of tissue
(derived in the previous section) and 1.66 kcal per gram of egg (presented
earlier), the following equation may be derived:
128
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where
Poultry
ME = 130 W075 (1.015) + 5.50 /\W + 2.07 EE,
W = body weight (kg),
/\W = growth rate or rate of loss in grams per day,
EE = egg mass (g), and
At = difference between 25°C and ambient temperature (°C).
129
The above equation assumes a temperature of 22°C at all experimental sta-
tions listed in Table 40, a most unlikely probability; yet the equations under-
estimated the observed ME values by only 3.2 percent. Seven values were
within + 5 percentage units of observed values. Unfortunately, experiments
available in the literature do not have details on ambient temperatures and
state of acclimation for the hens. Also to be noted is that heavy breeds were
included in the estimates of Table 40. Emmans (1974) considered these sepa-
rately. Nevertheless, the formula is a start, and the challenge is obvious.
Forced molting is practiced in the poultry industry. Less feed would be re-
quired to hold birds through a molt if buildings are kept warmer than usual.
Those occasions when ambient temperatures allow this are favorable periods
for the husbandry practice of forced molting. Use of fuel to attain desired
feed-saving temperatures is minimized. In open housing, molted hens are
stressed less at these warmer times of the year. The forced molting procedure
is not practiced with ambient temperature considered in the cost-accounting
of feed versus fuel. According to van Kampen (1974), an ambient tempera-
ture of 35°C reduces the HeE of feathered poultry to 57 kcal/W0 75. Although a
savings of feed at higher temperatures appears to be possible, and feed effi-
ciency is markedly improved, fuel costs and adverse physiological and nutri-
tional factors make high-temperature rearing of birds uneconomical.
WATER
Water is a nutrient essential for life. Free water consumption accounts for 74
percent of the total daily intake. Metabolic water is a secondary source, ac-
counting for 18 percent of the water intake. Temperature influences the pro-
portional accounting of the total water intake (see Table 101. Also, as ambi-
ent temperatures rise, chickens consume increasing amounts of water (Figure
24~. Such water intake is 2-fold and 2/2-fold at 32°C and 37°C, respectively,
above that at 21°C. Increasing ambient temperatures appear to cause body
temperature to rise slightly until ambient temperatures attain 38-39°C; then
higher air temperatures cause a marked rise in body temperature (Figure 24)
as the gradient between these two becomes less. The body heat is more diffi-
cult to remove, and physiological mechanisms (e.g., panting) are utilized to
assist heat loss, but these, in turn, generate heat from their activity, thereby
aggravating the situation. In domestic fowl, thermal polypnea increases
130 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT
40
-
30
LL
A
25
At:
20
15
10
; _
: _
0/
,=-13.1 + 1.23X
BT1 40.4 + 0.043 X
BT2 28.8 + 0.356 X /
~ O
o
o
O ~
· · /
_~. /~
/ O
/ O
_ If/
Body Temperature
(1)
to
/ O ~ it/
/Body
/ ( emperature
20 25 30 35 40 45
44
43 `'
o
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it:
it:
42 LL
UJ
o
41 m
40
TEMPE RATU R E ( C)
FIGURE 24. The relationship between ambient temperature and water intake or body tempera-
ture of White Leghorn hens in chambers for 6 hours (adapted data from Wilson, 1948).
steadily with increasing heat load, and energy utilized to remove heat re-
duces energy available for productivity. In addition, less feed is consumed as
ambient temperatures rise, and this also reduces net energy for production.
As the burden of heat stress becomes greater, the evaporative route (use of
water) for heat loss from poultry becomes more dominant.
Hyperventilation is used to increase evaporative heat loss. During such sit-
uations, the exchange of gases in the lungs increases with a concomitant re-
duction in the level of CO2 in the blood. This lowers the bicarbonate concen-
tration of the blood, resulting in an adverse effect on shell formation. Heat
stress produces its adverse effect on egg-shell quality in three ways: (1) by
interfering with calcium carbonate formation for shell, (2) by reducing feed
intake and thus calcium needed for shells, and (3) by upsetting the acid-base
Poultry
131
balance of the blood. Water plays an indirect role through its need to reduce
heat stress by allowing greater evaporative heat loss and as a media for salt
loss through secretory processes. Thus, poultry suffer even more when un-
able to obtain adequate water supplies during thermal stress.
Neither sweat glands nor sebaceous glands are found in the skin of poultry
(Jenkinson and Blackburn, 19681. Nevertheless, loss of cutaneous heat ac-
counts for 4~2 percent of the evaporative heat loss at ambient temperatures
of 1~20°C and 27 percent of the loss at 35°C (van Kampen, 1974~. The rel-
ative humidity of the air has an influence on the effectiveness of evaporative
heat loss. Hot, humid environments are particularly stressful for poultry un-
less they are acclimatized or acclimated to such conditions. However, rela-
tive humidities of 52 to 90 percent at temperatures of 12.6 or 23.8°C have no
effect on feed intake or weight gain (Prince et al., 1965~.
The availability of water for poultry is important for survival during heat
stress. Hens allowed ample drinking water in containers large enough to
dunk their heads survive longer during hot stressful conditions (Vo and
Boone, 19781. Thus, the water serves as a coolant for external evaporation or
to absorb heat from the head during drinking positions. In corroboration of
these observations, hens were noted to withstand high ambient temperatures
when allowed unlimited access to water, as compared to those given equiva-
lent amounts by syringe directly into the crop (Lee et al., 1945~. The conno-
tation of these data is that water presumed to be drunk during heat stress may
actually have been lost to the surroundings when shaken off the head. The
impact of such losses on total water intake is not known.
VITAMIN A
High ambient temperatures reduce the intake of diets by young chickens (As-
carelli and Bartov, 1963; Kurnick et al., 1964; Squibb et al., 1958) and lay-
ing hens (Heywang, 19521. In all experiments, these investigators noted that
the requirements of vitamin A did not change (Ascarelli and Bartov, 1963;
Heywang, 1952; Kurnick et al., 1964) or that absorption appeared to be un-
affected (Squibb et al., 1958) by higher temperatures. Instead the adjustment
of vitamin A levels in diets is required because of the reduced intake of feed
caused by high ambient temperatures.
SUMMARY
The optimum environment for rearing poultry is not necessarily that which
allows maximal gain in weight or egg output. Efficiency of productivity, in-
cluding cost factors, must also be considered. As environmental tempera-
tures vary, so do efficiency and cost of productivity. For example, diets high
in protein levels for maximum weight gain of turkeys seem most appropriate
132 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT
when protein is relatively cheap, but lower levels are justified when protein
is expensive. The ambient temperature influences feed intake and thus must
be considered in the profit-efficiency-weight gain output.
When nutrient intake is shifted by environmental influence on feed intake,
an adverse effect on productivity (growth or egg output) ought to be allevi-
ated by adjusting nutrient density to compensate for the altered intake of
feed. Nutrient requirement was considered to be altered when such adjust-
ments to give equal nutrient intake at different environmental conditions did
not yield comparable productive outputs and/or efficiency. Research with
poultry reveals that environmental temperatures over the range of 4 to 31°C
do not affect nutrient requirement for protein, lysine, or vitamin A, as mea-
sured by growth or egg production.
A review of experimental data revealed that feed intake of poultry appears
to change 1.5 percent per °C over the range of 5-35°C with 2~21°C as a
baseline. It decreases as temperatures rise, and vice versa. Maintenance en-
ergy is less at temperatures above 21°C and higher at lower temperatures.
Thus productive efficiency generally tends to improve as environmental tem-
peratures increase and be less efficient at colder temperatures. Energetic effi-
ciency of egg production considers such factors as weight of eggs produced,
percentage egg production, amount of feed consumed, and caloric density of
the diet. Tables are presented to allow the energetic efficiency to be deter-
mined from a set of values for each of the factors involved. These values are
based on how the energy value of an egg is calculated, and this is discussed.
The impact of body weight on energetic efficiency is noted, as well as how a
change in ambient temperature can influence energetic efficiency by influ-
encing a change in body weight.
Prediction equations are presented for estimating ME requirements of lay-
ing hens subjected to different ambient temperatures. One such derived equa-
tion is based upon a review of data in the literature. It differs from earlier
equations by adjustments of constants to reflect additional information gath-
ered during more recent experiments. These equations are expected to be a
challenge for future research to improve their predictability.
In cold environments hens are stimulated to eat more. Under such condi-
tions marginal deficiencies in nutrients appear to be overcome by the in-
crease in daily nutrient intake. On the other hand, hot environments may pro-
duce nutrient deficiencies for marginally adequate diets because of the
decline in feed intake. Making allowances for these situations by adjustment
of nutrient density appears to alleviate some, but not all, of the adverse ef-
fects from very hot conditions. Shell quality seems to be one of those in the
latter category.
Acclimation of poultry to continuous hot environments must be a consid-
eration in accounting for nutrient requirements. As little as 7 days, and as
Poultry
133
long as 28 days, were reported for poultry to acclimate. Differences in ad-
justment appear to be associated with such factors as age, species, tempera-
ture of stressful situations, and the type of productivity being measured.
Carcass composition will change during shifts in environmental tempera-
tures, and much of the change is related to the effect on feed intake and,
thus, nutrient intake.
As ambient temperatures rise, poultry consume increasing amounts of wa-
ter. Such water intake is 2-fold at 32°C, and 2/-fold at 37°C greater than the
intake at 21°C. The water plays an important role in evaporative heat loss
and to influence appetite, which accounts for less feed consumed as tempera-
tures rise. Thus energy used to dissipate the heat load, and a decline in en-
ergy available from the lower feed intake, reduces net energy available for
productivity. Availability of water for poultry is important for survival under
heat stress. There is some indication that poultry use the water as a coolant
for external evaporation, or to absorb heat from the head during drinking po-
sitions.
