Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
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
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
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).
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
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
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
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.
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).
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
118 ce JO cd ¢' o An cd ED In o cat :' cd so au Em ct On ·_. sit m o 4- ._ 3 o m Cd 00 go: Cd a_ . ~ _3 a' ~ A ~ an Hi 0 00 ~ C`, m ~ ¢ >\ o an i . - phi v a o ED Via _I a rat _ E ~ 3 m 3 ED ,jd == 3 ~ _1 3 m 3 of , Dirty _ ~ in: 3 To 3 to ,~ a., 3 It _ `, ^= 3' m 3 ,~ 0, 3 .= ~ Cd Y ,,~c o ._ ~ ~ ~ 13 ~ ~3 ~ ~ O ~D ~ oo ~ _ oo ~ ~ o - ~ - v~ ~D oo ~ _ ~ ~ C~ oo o ~ ~ - . . . . . . . . ~ oo O - ~ r~ ~ r~ ~ ~ _ _ _ _ 11 / - Io ~ l l ~ ~ ~ ~ I ~ r~ ~ O ~ . . . . . 1 ~ - ~ ~ ~ 1 - _ _ _ I t:5 I ,~ - 1 - cr~ 7 . . . ~ U~ ~ ~ ~ ~ C3 q3 t:3 ~ ~ - ~ a~ O ~ ~ ~ rn V~ ~ C~ ~ ~ ~ o ~ oo oo ~ - oo ~ - ~n . . . . . . . . ~ ~D ~ oo oO ~ O O 1 1 1 1~ 1= 0 - 10 1~) °° 1 oo 001-1 ~t ~ 1 -11~1 O ~ oo ~ ~ ~ oo O - ~ ~ - . . . . . . . . ~ ~ oo a~ ~ - c~ ~ _ ~ _ ~ <3 ~ too U~ ~ oo a~ 1' ') O ~ O ~ O ~ O U~ O oo oo a~ a~ 0 0 - - ~l . . . . . . . . . O O O O - - - - - c: Ct .= ._ . 0= c: ~ ~L) ·- Ct ~ ,_ ._ - ~ - ~ o - C) ~D 'e ct ~ c: =- so 3 ~ ~ oc .= 3 c, ~ 0 ~D c~ s.o e~ ~ ~ ._ ~ 3 ._ 3 't '~ c ~ ~4 . . o
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.
120 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT PERFORMANCE An improvement in growth performance may be observed upon a decline in ambient temperature as a result of an increase in feed consumption (Khalil et al., 19681. The response seems to occur as a result of an increased intake of diet, even though marginal in some nutrient rather than a response to temper- ature, per se. The former is the more likely reason, as March and Biely (1972) showed that a lysine deficiency at 31°C is not observed at 20°C be- cause of the greater amount of diet consumed at the lower temperature. Simi- larly, calculations based on data by Bray and Gesell (1961) reveal that hens at 5.5°C consume an average 23 percent more diet and, although fed diets with protein levels below normal, produced 18 percent more egg than their counterparts at 24.4°C on similar diets. Data by Bray and Gesell (1961) analyzed for response relationships be- tween daily egg mass produced (Y) and percentage protein in the diet (X) re- veal that for dietary protein levels ranging from 6 to 14 percent, Y = 11.7 + 4.06 X for hens kept at 30°C, and Y = 10.4 + 2.94 X for hens kept at 24.4°C. The slope ratio of 2.94/4.06 indicates that hens kept at 30°C ate 25 percent less diet, which attributed to the reduction in egg mass over the range of protein insufficiency. Based upon the slope of the response curves, each 1 percent decline in protein level below the dietary level of 12 percent results in a 4 g loss in egg weight. However, when egg mass is related to daily pro 60 ~ 50 - . _ - E - ~n In U] 40 30 20 18 Y = 7.716 + 2.91 X ·' - 0~' '0 ~ · O ~- EXPT1 ~ 0= 55 C _ / ~ ^=24.4°C ( · = 24.4°C EXPT 2 ~ ~ = 30 0°C _. 11 1 10 15 DAI LY PROTEIN INTAKE (gin/bird/day) 20 FIGURE 22. Relationship between dietary protein level and daily egg mass from White Leghorn hens at 5.5, 24.4, and 30°C (adapted from Bray and Gesell, 1961).
Poultry 121 tein intake rather than protein level in the diet, then a decline of 2.9 g of egg occurs for each 1 g of reduced protein intake below 14 g (Figure 22), regard- less of the temperature. At adequate protein intakes, moderately high tem- peratures do not affect egg mass output, provided energy intake is also com- parable. In cyclic environments chickens appear to take advantage of the cooler phase of the cycle to undo to some extent the adverse effect on production and quality caused by the extreme heat (de Andrade et al., 1977; Miller and Sunde, 1975; Squibb, 1959; Table 381. Temperatures in the lethal range, es- pecially those in tropical climates,-are tolerated so that egg production is maintained, but only if cooler temperatures occur at the lower range of the daily fluctuations (Squibb, 19591. However, chickens in heated chambers lay smaller eggs with thinner shells (Clark and Amin, 19651. Miller and Sunde (1975) noted that some hens shifted from cyclic cold to cyclic hot died, while others had several days of producing shell-less eggs. During hot sum- mer days when poultry are under stress to remove body heat and eat less diet, shifting the photoperiod to include cooler temperatures of the night would be appropriate to allow access to feed. ACCLIMATION Miller and Sunde (1975) noted that laying hens took 7 days to adjust to a shift of cyclic cold to cyclic hot. Jones et al. (1976) observed that chickens stabilized at lower values of feed intake within 24 hours when shifted to warmer temperatures. However, as long as 21 to 28 days were noted by other investigators (Davis et al., 1972; Shannon and Brown, 1969) for accli- mation to occur. Turkey hens appear to be acclimated, based on feed intake, in 8 to 14 days when shifted from cold to hot environments (Jones and Barnett, 1974), or, as long as 21 days, if the temperature is as high as 37.8°C (Parker et al., 19721. If they are moved stepwise every 2 weeks into 5°C hot- ter environments starting at 20°C, each time there are dramatic declines in productivity, feed intake, egg and shell quality, and estrone levels in plasma with the move into 30 and 35°C temperatures (Kohne and Jones, 19764. Evi- dently short-term exposure to a warmer environment does not acclimate tur- keys to a subsequently hotter environment. Unfortunately we have not taken advantage in everyday husbandry proce- dures of inducing acclimatization or acclimation as an approach to buffer an expected environmental impact. Most research has emphasized long-term constant exposure to a particular environmental factor, perhaps assuming ex- posure time would overcome the short-comings of our inability to study a multiple of variable factors.
122 APPROACHES FOR PRACTICAL NUTRITIONAL MANAGEMENT CARCASS COMPOSITION The effect of temperature on carcass composition is not an established cer- tainty. Fat levels in carcasses were shown to be unchanged (Adams et al., 1962; Mickelberry et al., 1966) or increased (Kubena et al., 1972; Winches- ter and Kleiber, 1938) as temperatures increase above 29°C. When lipid levels of the carcasses were increased, then investigators found the moisture levels decreased, a widely recognized phenomenon. Rearing chicks at 29°C did not alter the fatty acid composition of tissue (Fisher et al., 1962; Mick- elberry et al., 1966), but rearing them at 32°C did make them more saturated (Fisher et al., 19624. The trend for cold temperatures is that chickens (Fisher et al., 1965), turkeys (Hellickson et al., 1966), and ducks (Scott et al., 1959) have less fat. The chickens were noted to have fat that was more un- saturated (Fisher et al., 19651. Protein levels in the carcass may be un- changed (Kubena et al., 1972) or slightly lower (Olson et al., 1972) in hot ambient temperatures. Where chickens are restricted in their intake at cool cyclic temperatures ranging from 13 to 24°C, daily, to the amount consumed by birds at the hot temperatures (cyclic 26.5~0.5°C), then the difference in energy per unit gain (protein plus fat) could be considered that amount attrib- uted to the effect of temperature on feed intake. Olson et al. (1972) noted that those hot cyclic temperatures caused a decline of 49 percent in carcass energy gain when a diet with an ME of 3.22 kcal/g was fed, as compared to a decrease of 38 percent for a diet with ME of 3.69 kcal/g. In other words, tem- perature appears to influence carcass composition partially by its effect on feed intake and partially by altering the response of the animal. In hot envi- ronments, feed intake is less than normal, creating a nutrient deficit that may be severe enough to alter the metabolism of the liver, causing excess fat to accumulate in the carcass; whereas in cold temperatures, the demand for en- ergy may force depletion of adipose reserves for energy. Furthermore, in- creasing the energy density of the diet in cold weather will alleviate to some extent the demand to match intake with expenditure of energy and thus tend to maintain carcass composition at a status quo. During heat stress, when feed intake is reduced, the need for nutrients is alleviated to some extent by increasing nutrient density (Dale and Fuller, 1980), thus assuring less of a chance for a nutrient deficit, which can cause fat to accumulate in liver and carcass. NUTRIENT ADJUSTMENTS The heat increment of a hen's diet is lowest when a greater percentage of ME is in the form of lipid than when carbohydrates or protein dominate the ca- loric supply (Polin and Wolford, 1976~. Presumably, diets with minimal heat increment may be beneficial during periods of heat. The approach of adding
Poultry 123 fat to poultry diets during thermal stress has not been consistently successful. Reid (1979) achieved some success by adding up to 9 percent tallow in diets fed to laying hens reared at 29°C. Their ME intake per day increased, and this improved their energy balance, considering both egg production and body weight gain. On the other hand, Sell (1979) reported that increased caloric efficiency in laying hens fed added dietary fat during heat was due to tissue deposits of fat while egg energy per unit of ME consumed declined. Fat sup- plementation for broiler chickens has not been consistently beneficial during thermal stress. Fuller and Rendon (1977) and Dale and Fuller (1980) ob- tained beneficial results feeding high fat (29-33.2 percent of ME from fat) compared to low fat (7-12.6 percent of ME from fat) diets, but Cerniglia et al. (1978) found there was no advantage for adding dietary fat in diets fed to broilers during heat. Attempts to overcome the expected loss in feed intake and resultant ad- verse effects from high temperatures by adjusting nutrient density of the diet have met with partial success (Mowbray and Sykes, 1971; Payne, 19671. Stockland and Blaylock (1974) fed one of three diets to maintain protein in- take of hens relatively constant. Hens at 29.4°C produced at 66.4 percent versus 70.6 percent at ambient (March-July), or 68 percent at 18.3°C, de- spite a 19 percent decline in feed intake. The experiment lasted 26 weeks. Table 40 summarizes data (de Andrade et al., 1976, 1977) that compare diets whose nutrients were increased 2~25 percent and the energy density by 10 percent over that of a diet typically used at thermoneutrality. All three diets were fed to laying chickens in three different environments. The higher nutrient densities prevented a major decline in egg production, moderated a decline in egg weight, markedly improved efficiency of feed conversion to egg, but were unable to prevent the loss in shell quality (Table 39~. Part of the reason for the latter's decline is attributed to a 6.5-13.5 percent lower calcium intake (Table 39~. Another reason for poor shell quality during heat stress appears to be lower circulating levels of hormones, for chickens (Bell and Freeman, 1971; de Andrade et al., 1977; Erb et al., 1978) and turkeys (Kohne and Jones, 1976), and the physiological stress of respiratory alka- losis (Mongin, 19681. Just having adequate calcium intake without an ade- quate intake of other nutrients does not overcome the effect of temperature on shell calcium (Kohne and Jones, 19761. At equal calcium intakes, the hot temperatures lower shell quality (Figure 231. Overall,~the indication is that nutrient intake alone is not going to solve completely the adverse effect of heat stress. There is that physiological stress on laying birds during initial heat exposure that dietary changes do not ap- pear to moderate. Miller and Sunde (1975) observed shell-less eggs and some mortality within 24 hours after subjecting laying hens to cyclic or con- stant hot environments. They detected an effect on shell quality of those eggs in the shell gland within the few hours after heat exposure. In time some ac
124 4 - ~ .~ .o ._ <t 3 ._ ~ o ~ of lo, 11 - 1 11 Cal Cal ~ _ Cal o [Lo ._ s°- ~ C.) .= ~ Ct ~ ~ ¢ o _ ~ ¢ st ~ ~ _ ~ Ct _ A ~ s°- o to ~ ~ to Ct (lo Cal Em C: o 0 11 C) I ~ 4_ Ct Ct <D Q me ~ _ an Ha; at EM ~ EM O ~ ~ ~ ~ ~ _ o c~ c ) o ~ cr. ~ o~ - o + -o Ct ~ ~ ~ o ~ ~ ~o V) o ~ c ;> "yo~ u, m ~ Ct tV ~ 43 ~ a~ ,$ a~ _ Ct _` - a' `` `,, _ _ 00 O _ ~ m} ~ ~ ~ 0 0 ~ ~1 1 1 1 1 _ _ 0 _ _ 1 1 o 0 0 _ ° 1 r~ 00 + 1 g o 0 8 C~ 00 1 1 0 o 1 1 1 00 1 0 ° 1 1 V o ~ ~ 4_ - - c~ ~ ~ r~ ~ ~ a, Ct r O C~ C~ C~ ~_ C) _ _ cd _ a~ ~ Ct C~ ~ ~ O ~ ~ ·~ 0D ~7 ~ au C~ ~ ~ ~y J: ~ .= V E~ 3 ~ - C~ ~ _ ~: . ~ ;^ ;> ~ ~ m ~o o ca a~ _ _ Ct C~ ~ :S _ _ ~ C~ ~q~
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 ca ~ so - ~ 2 an o Cal _ ~ ° a., at o au C) of a: Ct 4 - a' o 4- to Cal en ca so 3 Cal ._ o C) a' au Em · Ct - o ._ - o o EM _` A_ to _ . _ Ct ¢ au s°- Ct ¢ by . Ct O a' EM 11 ~ 'tub EM ° I_ Ct o o Ct - on on -` cd c: .-o c) + $ o + z $ o + z o + z ~ - o ~n + $ o + a $ o _ O .>o ~i ~ 00 0 ~ . . . 00 '_ 1 1 1 00 _ 1 1 1 00 ~ . . 0 ~ ~ _. tl I I ~ - ~ 1 1 1 oo . ~ o 1 1 1 . . o C~ tl I I ~ oo ro . . . o + 1 1 . . 0 a~ 1 1 1 . . o ~ oo _4 tl I I o~ V V - o ~ ~ C Ct C ) Ce CD - CD ~ C) C: o ;^ o V V V z $ o + ~ $ ._ C) a ~ C~ .Y E~ - ~: V, ~4 ._ 3 ~4 oc + z :r o + $ c: V U~ C~ + o c~ + z $ o ~ oo ~ . . . ~ ~ ~o - + 1 1 o ~ . . a~ ~ - + 1 1 ~ - . . o ~ ~ r~ tl I I ~ oo ~ . . . o ~ _ - + 1 1 . . ~ ~D + 1 1 . . o oo _ - tl I I . . . _ ~ ~ + 1 1 _ ~o . . + 1 1 o ~ ~ ~ oo tl I I V o ~ o ~ o = - ~ Ct ~ Ct o ~ o V V ~ - ~o ~o ~: 4_ o o C) C~ Ct C) a~ o - ~D ._ Ct X ,= ~4 4- a' ·= ~ ~ ~, - ( ~ c', o ~ C ~ ~ ·= o C~ o au c Ce X C) ~ ._ o ~ ~o =: ~-o, 3 Ct au Ct 11 11 o + + z z $ :~:
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 · _. ~ Go Go t- _' _' _ Ct t c ~ o C) ~ - 'V 3 ~t _ ~ a; Cal c: Cal o ·c CL o ·5 to c'J o + A o + a ^ 4_ _ [.L1 0 - c: ~ 0 Cal _ 0 11 ~ 0 A_ m ~ Ed . Ct o 00 _ A_ O _ _ c: ~ Cal _% o - ~ ) ~ ( Cal _ ~ C\l L -,= C~ - O ~ ~: o ._ ~0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ cr. - ~ ~ oo ~ . . . . . . . . . . . . . . . . ~ ~ O ~ ~ ~ ~ ~ ~ ~ ~ ~ C~ oo ~ ~ _ _ 1 + + 1 1 1 + 1 + 1 1 1 1 1 1 1 ________________ ~ O ~ O . . . . ~ ~ ~ ~n 0 - cr~ - . . ~ ~0 1 +1 . . . . . X _ ~ _ O ~ ~ O . - 1 ~ ~ ~t ~ ~ U~ _ oo ~ . . . . . O ~ O 0\ ~ ~ ~ U~ ~ == o ~ U~ ~ - X O ~ ~ 0\ ~ O ~ ~ ~ - _ ao ~ _ oo o ~ oo ~ oo O ~ ~ ~ ~ - _ 1 + + 1 _ _ _ _ O - U~ oo ~ _ _ _ ~ ~ - 1 + 1 + + 1 1 + 1 + + ___________ ~ U~ ~ ~ ~ ~ ~ ~ o ~ oo . . . . . . . . . . . O ~ ~ oo oo ~ ~ O _ ~ ~ ~ ~ ~ O - ~ ~ C~ ~ . . . . ~ oo ~ ~ _ _ + + + + ~ ~ oo cr. . . . . _ _ o ~ O. ~ ~ ~ _ O ~ ~ O ~ _ _ + + I I I tl + I + - - - - - - - - - - - - - - - oo ~ o o - . . . . . ~ o ~ oo ~ r~ u~ + tl o . . + tl ~ ~ _ oo . . . . - o ~ ~ ~ oo ~ cr ~ . . . . . _ ~ ~ ~ ~ ..... _ _ _% _ _` _ _- _ _ _- _ _ _ ~ ~ oo o _ _ + tl ~ ~ ~ ~ ~ 0 o~ ~ r~ oo - ~t ~ t- (~ ~ . . . . . . . . . . . . . . . . oo r~ ~ ox ~ - ~ oo ~ ~ ~ co - r - , ~ _ ~ ~ _ ~ _ _ ++++++++++++++++ _______________ O O O oo O ~ ~ ~ O ~ ~ oo ~ . . . . . . . . . . . . . . . oo v~ oo ~ ~ ~ ~ ~ ~ ~ ~ ~D oo a~ o ~ oo ~ ~ oo ~ ~ ~ ~ ~ ~ _ r~ ~D d- ~ ~ ~ t- - ON ~ ~t oo - . . . . . . . . . . . . . . ~ o ~ ~ ~ - ~ ~ ~ ~ ~ o ~ o ON =~ ~ ~) _ oo ~ ~ U~ ~ - o r~ ~ ~ ~ ~ ~ r~ o ·S ~ ~ ~ ~ ~4,) _ m o~o ~ m 2 11 ~_ oo a~ ~ 2 ce . - ~: ~ o ~ - s O s ~^ ~ ~,, ~ ~ e ,~ C: ~ ~ Z ~ ~ ~ Z V, D Ct
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 UJ 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.