2
Nutrient Requirements of Chickens

Chickens vary greatly according to the purpose for which they have been developed. Those intended for the production of eggs for human consumption (Leghorn-type) have a small body size and are prolific layers, whereas those used as broilers or broiler breeders (meat-type) have rapid growth rates and a large body size. They are less efficient egg layers. Methods of feeding differ for these two kinds of chickens.

LEGHORN-TYPE CHICKENS

Methods of feeding Leghorn-type chickens depend on the age and activity (laying or breeding) of the bird. Feed requirements change as birds pass through the starting and growing, pre-egg-laying, egg production, and molt phases.

Starting and Growing Pullets

Relatively little research has been conducted in the last 10 years to obtain definitive nutrient requirements for immature Leghorn-type birds. In large part, this situation is due to the use of meat-strain birds in requirement studies involving avian species. Thus, although growth and maturity characteristics of egg-strain pullets have changed considerably over the last 10 years, particularly for brown-egg-laying birds, the only data available on requirements for many nutrients are dated. Most current research activity deals with nutrients of major economic significance. The available information is reviewed in Appendix Table A-1.

Nutrient requirements of immature Leghorn-type chickens (pullets) are listed in Table 2-1. Although requirements are assessed ultimately in terms of subsequent reproductive performance, the criteria used by the committee were adequate growth rate (in terms of final body weight at different ages) and normal metabolism. It is well documented that mature body weight can greatly influence the subsequent reproductive performance (Leeson and Summers, 1987a), and, as such, this criterion becomes critical in the assessment of nutritional status.

The dearth of research information for immature pullets is even more acute for brown-egg-laying strains. Because brown-egg-laying birds predominate in many parts of the world, the committee has attempted to define their nutrient requirements as well. In large part, however, these requirement values have been extrapolated from studies conducted with Leghorns with consideration for the larger body weight and/or appetite and increased maintenance requirement of brown-egg layers.

The nutrient requirement values shown in Table 2-1 and the performance characteristics shown in Table 2-2 are based on the assumption that the birds will be allowed to consume feed in an ad libitum manner. Ad libitum feed consumption is important for Leghorn birds, especially when reared in hot climates, because of their inherently low appetites. Managers should routinely consider restricted feeding only for brown-egg-laying strains, and even then only in temperate climates and with high-energy diets.

PROTEIN AND ENERGY

In discussing the protein needs of growing pullets, it is assumed that the amino acid profile is balanced according to the requirement values shown in Table 2-1. Pullets allowed to self-select diets based on protein or energy content seem to voluntarily consume much less protein in early life and more protein as they approach maturity (Summers and Leeson, 1978) than do pullets on more conventional programs. However, low-protein or low-lysine starter diets invariably depress the growth



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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 2 Nutrient Requirements of Chickens Chickens vary greatly according to the purpose for which they have been developed. Those intended for the production of eggs for human consumption (Leghorn-type) have a small body size and are prolific layers, whereas those used as broilers or broiler breeders (meat-type) have rapid growth rates and a large body size. They are less efficient egg layers. Methods of feeding differ for these two kinds of chickens. LEGHORN-TYPE CHICKENS Methods of feeding Leghorn-type chickens depend on the age and activity (laying or breeding) of the bird. Feed requirements change as birds pass through the starting and growing, pre-egg-laying, egg production, and molt phases. Starting and Growing Pullets Relatively little research has been conducted in the last 10 years to obtain definitive nutrient requirements for immature Leghorn-type birds. In large part, this situation is due to the use of meat-strain birds in requirement studies involving avian species. Thus, although growth and maturity characteristics of egg-strain pullets have changed considerably over the last 10 years, particularly for brown-egg-laying birds, the only data available on requirements for many nutrients are dated. Most current research activity deals with nutrients of major economic significance. The available information is reviewed in Appendix Table A-1. Nutrient requirements of immature Leghorn-type chickens (pullets) are listed in Table 2-1. Although requirements are assessed ultimately in terms of subsequent reproductive performance, the criteria used by the committee were adequate growth rate (in terms of final body weight at different ages) and normal metabolism. It is well documented that mature body weight can greatly influence the subsequent reproductive performance (Leeson and Summers, 1987a), and, as such, this criterion becomes critical in the assessment of nutritional status. The dearth of research information for immature pullets is even more acute for brown-egg-laying strains. Because brown-egg-laying birds predominate in many parts of the world, the committee has attempted to define their nutrient requirements as well. In large part, however, these requirement values have been extrapolated from studies conducted with Leghorns with consideration for the larger body weight and/or appetite and increased maintenance requirement of brown-egg layers. The nutrient requirement values shown in Table 2-1 and the performance characteristics shown in Table 2-2 are based on the assumption that the birds will be allowed to consume feed in an ad libitum manner. Ad libitum feed consumption is important for Leghorn birds, especially when reared in hot climates, because of their inherently low appetites. Managers should routinely consider restricted feeding only for brown-egg-laying strains, and even then only in temperate climates and with high-energy diets. PROTEIN AND ENERGY In discussing the protein needs of growing pullets, it is assumed that the amino acid profile is balanced according to the requirement values shown in Table 2-1. Pullets allowed to self-select diets based on protein or energy content seem to voluntarily consume much less protein in early life and more protein as they approach maturity (Summers and Leeson, 1978) than do pullets on more conventional programs. However, low-protein or low-lysine starter diets invariably depress the growth

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 TABLE 2-1 Nutrient Requirements of Immature Leghorn-Type Chickens as Percentages or Units per Kilogram of Diet     White-Egg-Laying Strains Brown-Egg-Laying Strains Nutrient Unit 0 to 6 Weeks; 450 ga 2,850b 6 to 12 Weeks; 980 ga 2,850b 12 to 18 Weeks; 1,375 ga 2,900b 18 Weeks to First Egg; 1,475 ga 2,900b 0 to 6 Weeks; 500 ga 2,800b 6 to 12 Weeks; 1,100 ga 2,800b 12 to 18 Weeks; 1,500 ga 2,850b 18 Weeks to First Egg; 1,600 ga 2,850b Protein and amino acids Crude proteinc % 18.00 16.00 15.00 17.00 17.00 15.00 14.00 16.00 Arginine % 1.00 0.83 0.67 0.75 0.94 0.78 0.62 0.72 Glycine + serine % 0.70 0.58 0.47 0.53 0.66 0.54 0.44 0.50 Histidine % 0.26 0.22 0.17 0.20 0.25 0.21 0.16 0.18 Isoleucine % 0.60 0.50 0.40 0.45 0.57 0.47 0.37 0.42 Leucine % 1.10 0.85 0.70 0.80 1.00 0.80 0.65 0.75 Lysine % 0.85 0.60 0.45 0.52 0.80 0.56 0.42 0.49 Methionine % 0.30 0.25 0.20 0.22 0.28 0.23 0.19 0.21 Methionine + cystine % 0.62 0.52 0.42 0.47 0.59 0.49 0.39 0.44 Phenylalanine % 0.54 0.45 0.36 0.40 0.51 0.42 0.34 0.38 Phenylalanine + tyrosine % 1.00 0.83 0.67 0.75 0.94 0.78 0.63 0.70 Threonine % 0.68 0.57 0.37 0.47 0.64 0.53 0.35 0.44 Tryptophan % 0.17 0.14 0.11 0.12 0.16 0.13 0.10 0.11 Valine % 0.62 0.52 0.41 0.46 0.59 0.49 0.38 0.43 Fat Linoleic acid % 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Macrominerals Calciumd % 0.90 0.80 0.80 2.00 0.90 0.80 0.80 1.80 Nonphytate phosphorus % 0.40 0.35 0.30 0.32 0.40 0.35 0.30 0.35 Potassium % 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Sodium % 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Chlorine % 0.15 0.12 0.12 0.15 0.12 0.11 0.11 0.11 Magnesium mg 600.0 500.0 400.0 400.0 570.0 470.0 370.0 370.0 Trace minerals Manganese mg 60.0 30.0 30.0 30.0 56.0 28.0 28.0 28.0 Zinc mg 40.0 35.0 35.0 35.0 38.0 33.0 33.0 33.0 Iron mg 80.0 60.0 60.0 60.0 75.0 56.0 56.0 56.0 Copper mg 5.0 4.0 4.0 4.0 5.0 4.0 4.0 4.0 Iodine mg 0.35 0.35 0.35 0.35 0.33 0.33 0.33 0.33 Selenium mg 0.15 0.10 0.10 0.10 0.14 0.10 0.10 0.10 Fat soluble vitamins A IU 1,500.0 1,500.0 1,500.0 1,500.0 1,420.0 1,420.0 1,420.0 1,420.0 D3 ICU 200.0 200.0 200.0 300.0 190.0 190.0 190.0 280.0 E IU 10.0 5.0 5.0 5.0 9.5 4.7 4.7 4.7 K mg 0.5 0.5 0.5 0.5 0.47 0.47 0.47 0.47 Water soluble vitamins Riboflavin mg 3.6 1.8 1.8 2.2 3.4 1.7 1.7 1.7 Pantothenic acid mg 10.0 10.0 10.0 10.0 9.4 9.4 9.4 9.4 Niacin mg 27.0 11.0 11.0 11.0 26.0 10.3 10.3 10.3 B12 mg 0.009 0.003 0.003 0.004 0.009 0.003 0.003 0.003 Choline mg 1,300.0 900.0 500.0 500.0 1,225.0 850.0 470.0 470.0 Biotin mg 0.15 0.10 0.10 0.10 0.14 0.09 0.09 0.09 Folic acid mg 0.55 0.25 0.25 0.25 0.52 0.23 0.23 0.23 Thiamin mg 1.0 1.0 0.8 0.8 1.0 1.0 0.8 0.8 Pyridoxine mg 3.0 3.0 3.0 3.0 2.8 2.8 2.8 2.8 NOTE: Where experimental data are lacking, values typeset in bold italics represent an estimate based on values obtained for other ages or related species. a Final body weight. b These are typical dietary energy concentrations for diets based mainly on corn and soybean meal, expressed in kcal MEn/kg diet. c Chickens do not have a requirement for crude protein per se. There, however, should be sufficient crude protein to ensure an adequate nitrogen supply for synthesis of nonessential amino acids. Suggested requirements for crude protein are typical of those derived with corn-soybean meal diets, and levels can be reduced somewhat when synthetic amino acids are used. d The calcium requirement may be increased when diets contain high levels of phytate phosphorus (Nelson, 1984).

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 TABLE 2-2 Body Weight and Feed Consumption of Immature Leghorn-Type Chickens   White-Egg-Laying Strains Brown-Egg-Laying Strains Age (weeks) Body Weighta (g) Feed Consumption (g/week) Body Weighta (g) Feed Consumption (g/week) 0 35 50 37 70 2 100 140 120 160 4 260 260 325 280 6 450 340 500 350 8 660 360 750 380 10 750 380 900 400 12 980 400 1,100 420 14 1,100 420 1,240 450 16 1,220 430 1,380 470 18 1,375 450 1,500 500 20 1,475 500 1,600 550 a Average genetic potential when feed is consumed on an ad libitum basis. Different commercial strains may show different growth rates and different final mature body weights. rate of both white-egg- (Douglas and Harms, 1982; Kwakkel et al., 1991) and brown-egg-laying pullets (Maurice et al., 1982), and early growth depression often depresses mature body weight and thereby adversely affects adult performance (Milby and Sherwood, 1953; Leeson and Summers, 1979, 1987a). Low-protein diets have a transitory effect on muscle fiber size rather than any long-term effect on numbers of such fibers (Timson et al., 1983). Although low-protein diets seem to adversely affect growth rate, there is little indication that excessively high levels of protein have any benefit on growth and development. Data of Keshavarz (1984) and Leeson and Summers (1989) suggest that in Leghorn pullets reduction in growth is often seen when total protein intake to 140 days of age is less than 1 kg. An intake of 1 kg of balanced protein during the same period seems to result in maximum growth. Energy intake may be the limiting factor for growth of egg-strain birds reared under most environmental conditions. Assuming no amino acid deficiency, and an intake of 1 kg of protein from 1 day to 20 weeks, growth and development seem most responsive to energy intake (Leeson and Summers, 1989). A total intake of 21 Mcal ME to 20 weeks seems ideal for white-egg-laying pullets. However, manipulation of energy intake is not always easy, since the pullet appears to have a fairly precise innate ability to regulate its energy intake regardless of dietary energy level (Cunningham and Morrison, 1976; McNaughton et al., 1977b; Doran et al., 1983). Manipulation of energy intake is, therefore, best considered in relation to feeding management and, in particular, methods of stimulating feed intake. For example, feed intake may be increased through use of pelleted feed, increased frequency of feeding, feeding at cooler times of the day, and, where possible, use of longer periods of light. Leeson and Summers (1989) concluded that pullet growth is initially most sensitive to dietary protein and amino acids, whereas energy intake becomes more critical as the bird approaches maturity. Skeletal size has also been considered as a criterion for assessment of pullet development. Lerner (1946) suggested that skeletal size is a limiting factor for growth, and Jaap (1938) indicated that shank length can be used as a reliable estimate of skeletal size per se. Skeletal development is related to adequate supplies of calcium, phosphorus, and vitamin D3, although deficiencies of most nutrients can adversely affect normal vascularization of cartilage at the growth plate, a prerequisite to normal calcification (Leeson and Summers, 1988). Skeletal growth is intimately associated with general growth and development, and it is difficult to influence either independently. Leeson and Summers (1984) indicated that increased skeletal size of pullets in response to dietary protein was associated with reduced ash content of bones. MINERALS AND VITAMINS As indicated above, little work has been done recently to evaluate the mineral and vitamin requirements of young egg-strain birds. There has been some interest in reevaluating nonphytate phosphorus needs, although, in general, the new data indicate no major change in previously reported requirement values. Both the young white-egg- (Douglas and Harms, 1986) and the young brown-egg-laying pullets (Carew and Foss, 1980) exhibit an inferior growth rate when fed starter diets containing less than 0.4 percent nonphytate phosphorus. The sodium requirement of the Leghorn pullet is approximately 0.15 percent of the diet regardless of age, although somewhat lower levels can be used after 10 weeks of age if excessive water intake is problematic (Manning and McGinnis, 1980). Prelay Period Daily nutrient requirements of pullets 10 to 17 days before first egg are generally considered to be greater than during the preceding 4 to 6 week period, although there is little evidence to show that pullets cannot meet these requirements through increased voluntary feed intake. Hoyle and Garlich (1987) found no change in growth or development of Leghorn pullets in response to elevated levels of dietary energy or protein. As suggested above, energy intake is probably the most critical component for this age of bird, and energy intake can perhaps be manipulated best through stimulation of feed intake rather than by simply increasing the energy level of the feed.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 The committee's review of research on the changes in metabolism of medullary bone immediately prior to maturity has led to reevaluation of the pullets' requirement for calcium at this time. Since modern egg-strain pullets exhibit a rapid increase in egg production and prolonged first multiegg clutch, it is obvious that a change in the requirements related to calcification must be accommodated before or at time of first egg. Keshavarz (1987) indicated that feeding a diet containing 3.5 percent calcium from as early as 14 weeks of age had no adverse effect on skeletal integrity, apparent renal function, or subsequent reproductive performance. Leeson et al. (1986, 1987a) also observed normal pullet development, skeletal integrity, and kidney histology when immature 19-week-old pullets were fed diets containing 3.5 percent calcium. These same workers indicated that calcium levels of 0.9 to 1.5 percent at this age were detrimental to early shell quality. In studies in which pullets were allowed to self-select nutrients, Classen and Scott (1982) showed that the birds consumed calcium in relation to needs for deposition of medullary bone and (or) onset of shell calcification. There has been little research on the phosphorus and vitamin D3 requirements of the prelay pullet. Hens in Egg Production Progress continues in the quest to use less feed in producing eggs. Most of this progress has resulted from decreasing the amount of feed that is required for body maintenance of laying hens. BODY MAINTENANCE NEEDS Management practices, as well as nutritional regimes, can affect the maintenance requirement. In warmer houses, layers need less energy from their feed because they expend less energy in maintaining body temperature. Hens eat less feed with increasing temperatures and decrease feed consumption drastically at temperatures above 30°C (Davis et al., 1973; National Research Council, 1981c). Genetic selection can also affect the amount of feed required for maintenance. With chickens bred for higher rates of egg production, there is a decrease in the maintenance requirement relative to eggs produced. At a rate of 100 percent egg production (that is, one egg per hen per day), maintenance requirements must be fulfilled for the 12 days needed to produce a dozen eggs; at a rate of 75 percent egg production, 16 days of maintenance requirements must be met to obtain a dozen eggs. Body size also affects maintenance requirements. A compilation of information from nonpasserine birds showed that basal metabolism was equal to 78.3 kcal per day × (kg body weight)723 (Lasiewski and Dawson, 1967). Conditions for collection of these data were that the birds were in a postabsorptive state, in a thermoneutral environment, and as nearly at rest as possible. Maintenance requirement, or the energy needed to sustain normal body processes and activities other than growth and egg production, is greater than that of basal metabolism. In the thermoneutral range of temperatures, maintenance for hens is approximately 100 kcal per day per kg body weight (MacLeod and Jewitt, 1988; Pesti et al., 1990). Strains of hens may differ in their maintenance needs because of metabolic or behavioral characteristics (Pesti et al., 1990). PRODUCTION NEEDS Nutritional factors can affect the amount of feed required to produce eggs. For example, some research indicates that hens are able to make a good adjustment of feed intake to provide nearly identical daily energy intakes with up to 6 percent added dietary fat (Sell et al., 1987). But other research suggests that the hen is not very accurate in adjusting feed intake to provide equal daily energy intake when offered a range of dietary energy conditions (Morris, 1968; Rising et al., 1989). Regardless of the accuracy of energy adjustment, hens eat less of a high-energy, nutritionally balanced feed than of a low-energy feed to produce a dozen eggs. Now that eggs can be produced with less feed, nutritionists have been permitted, or sometimes forced, to formulate diets differently than they did several years ago. Generally, it is assumed that a hen's daily requirements for nutrients, other than energy, are not changed by the level of feed consumption. If this is correct, then the difference in composition between the diet of a layer eating 80 g of feed per day and the diet of one eating 120 g of feed per day should be about 40 g of energy-supplying ingredients. But differences in daily feed consumption can cause the need for dramatic differences in dietary nutrient concentration, if diets are formulated to supply a specified amount of nutrient, other than energy, each day. Nutrient requirements of egg-type laying hens (Table 2-3) are expressed in terms of dietary concentrations for three levels of daily feed consumption. (The research reports on which the committee based its nutrient requirement decisions are listed in Appendix Table A-2.) Just how different rates of feed consumption can influence the formulation of a diet can be seen by using one nutrient—say, lysine, as an example. The lysine required each day by a white-egg-laying hen is 690 mg, or 0.69 g. Thus the diet of a white-egg-laying layer eating 100 g of feed per day should have a lysine concentration of 0.69 percent.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 TABLE 2-3 Nutrient Requirements of Leghorn-Type Laying Hens as Percentages or Units per Kilogram of Diet (90 percent dry matter)     Dietary Concentrations Required by White-Egg Layers at Different Feed Intakes Amounts Required per Hen Daily (mg or IU)     White-Egg Breeders at 100 g of Feed per Hen Dailyb White-Egg Layers at 100 g of Feed per Hen Daily Brown-Egg Layers at 110 g of Feed per Hen Dailyc Nutrient Unit 80a,b 100a,b 120a,b Protein and amino acids Crude proteind % 18.8 15.0 12.5 15,000 15,000 16,500 Argininee % 0.88 0.70 0.58 700 700 770 Histidine % 0.21 0.17 0.14 170 170 190 Isoleucine % 0.81 0.65 0.54 650 650 715 Leucine % 1.03 0.82 0.68 820 820 900 Lysine % 0.86 0.69 0.58 690 690 760 Methionine % 0.38 0.30 0.25 300 300 330 Methionine + cystine % 0.73 0.58 0.48 580 580 645 Phenylalanine % 0.59 0.47 0.39 470 470 520 Phenylalanine + tyrosine % 1.04 0.83 0.69 830 830 910 Threonine % 0.59 0.47 0.39 470 470 520 Tryptophan % 0.20 0.16 0.13 160 160 175 Valine % 0.88 0.70 0.58 700 700 770 Fat Linoleic acid % 1.25 1.0 0.83 1,000 1,000 1,100 Macrominerals Calciumf % 4.06 3.25 2.71 3,250 3,250 3,600 Chloride % 0.16 0.13 0.11 130 130 145 Magnesium mg 625 500 420 50 50 55 Nonphytate % 0.31 0.25 0.21 250 250 275 phosphorusg Potassium % 0.19 0.15 0.13 150 150 165 Sodium % 0.19 0.15 0.13 150 150 165 Trace minerals Copper mg ? ? ? ? ? ? Iodine mg 0.044 0.035 0.029 0.010 0.004 0.004 Iron mg 56 45 38 6.0 4.5 5.0 Manganese mg 25 20 17 2.0 2.0 2.2 Selenium mg 0.08 0.06 0.05 0.006 0.006 0.006 Zinc mg 44 35 29 4.5 3.5 3.9 Fat soluble vitamins A IU 3,750 3,000 2,500 300 300 330 D3 IU 375 300 250 30 30 33 E IU 6 5 4 1.0 0.5 0.55 K mg 0.6 0.5 0.4 0.1 0.05 0.055 Water soluble vitamins B12 mg 0.004 0.004 0.004 0.008 0.0004 0.0004 Biotin mg 0.13 0.10 0.08 0.01 0.01 0.011 Choline mg 1,310 1,050 875 105 105 115 Folacin mg 0.31 0.25 0.21 0.035 0.025 0.028 Niacin mg 12.5 10.0 8.3 1.0 1.0 1.1 Pantothenic acid mg 2.5 2.0 1.7 0.7 0.20 0.22 Pyridoxine mg 3.1 2.5 2.1 0.45 0.25 0.28 Riboflavin mg 3.1 2.5 2.1 0.36 0.25 0.28 Thiamin mg 0.88 0.70 0.60 0.07 0.07 0.08 NOTE: Where experimental data are lacking, values typeset in bold italics represent an estimate based on values obtained for other ages or related species. a Grams feed intake per hen daily. b Based on dietary MEn concentrations of approximately 2,900 kcal/kg and an assumed rate of egg production of 90 percent (90 eggs per 100 hens daily). c Italicized values are based on those from white-egg layers but were increased 10 percent because of larger body weight and possibly more egg mass per day. d Laying hens do not have a requirement for crude protein per se. However, there should be sufficient crude protein to ensure an adequate supply of nonessential amino acids. Suggested requirements for crude protein are typical of those derived with corn-soybean meal diets, and levels can be reduced somewhat when synthetic amino acids are used. e Italicized amino acid values for white-egg-laying chickens were estimated by using Model B (Hurwitz and Bornstein, 1973), assuming a body weight of 1,800 g and 47 g of egg mass per day. f The requirement may be higher for maximum eggshell thickness. g The requirement may be higher in very hot temperatures.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 Hens eating 80 g of feed per day need a dietary lysine concentration of 0.86 percent to obtain 0.69 g per day; hens eating 120 g per day need a dietary lysine concentration of only 0.58 percent lysine to provide 0.69 g per hen per day. The basic concept is that high daily feed consumption permits low nutrient concentrations and low daily feed consumption demands high nutrient concentrations. Equations have been developed to predict the energy required by chickens during egg production (McDonald, 1978; National Research Council, 1981c). These equations use the expected energy requirements of hens as related to body weight, daily egg mass, change in body weight, and ambient temperature to predict a total daily energy requirement. The data of Table 2-4 show the predicted daily energy requirements of hens as related to different body weights and rates of egg production, assuming no change in body weight and an ambient temperature of 22°C. The energy requirements derived from such calculations can be used to estimate daily feed intake by relating the hen's energy needs to the dietary energy concentration. Diets for laying hens, however, can be most accurately formulated on the basis of feed intake data obtained frequently (every 1 to 2 weeks) for individual flocks. Most egg-type hens are given ad libitum access to feed; however, feeding programs may be modified after the maximum rate of egg mass output has been attained (Cerniglia et al., 1984; Cunningham, 1984). Laying hens eat more feed than is needed to support egg production. As a result, it may be more profitable to limit their feed intake. Doing so would also reduce the likelihood of health problems that can also result when hens are overly fat. Data on feed consumption in individual flocks, together with information on body weight, ambient temperature, and rate of egg production, may be used to determine the degree of feed restriction deemed appropriate. Phase Feeding Nutrient requirements presented in Table 2-3 assume that the amount of nutrient needed each day remains the same throughout a hen's time of production. Some feeding programs, however, are based on the assumption that the amount of nutrient needed each day is different at different stages of the production cycle. These programs are called phase feeding. In phase feeding for flocks of laying hens, Phase 1 is designated as the time from the onset of egg production until past the time of the maximum egg mass output, usually at about 36 weeks of age, which is the time of maximum egg mass output. Phase 2 is the period between 36 and approximately 52 weeks, a period of high but declining egg production and increasing egg weight. Phase 3 is from about 52 weeks to the end of the production cycle, in some instances to 80 weeks. During TABLE 2-4 Estimates of Metabolizable Energy Required per Hen per Day by Chickens in Relation to Body Weight and Egg Production (kcal) Body Weight (kg) Rate of Egg Production (%)   0 50 60 70 80 90 1.0 130 192 205 217 229 242 1.5 177 239 251 264 276 289 2.0 218 280 292 305 317 330 2.5 259 321 333 346 358 371 3.0 296 358 370 383 395 408 NOTE: A number of formulas have been suggested for prediction of the daily energy requirements of chickens. The formula used here was derived from that in Effect of Environment on Nutrient Requirements of Domestic Animals (National Research Council, 1981c): ME per hen daily = W0.75 (173 - 1.95T) + 5.5 dW + 2.07 EE where W = body weight (kg), T = ambient temperature (°C), dW = change in body weight (g/day), and EE = daily egg mass (g). Temperature of 22°C, egg weight of 60 g, and no change in body weight were used in calculations. Phase 3 the rate of egg production continues to decline while egg weight increases only slightly. A phase feeding program adjusts daily nutrient intakes according to expected requirements for maintenance and egg production. Generally, daily intakes of protein, amino acids, and phosphorus are reduced with each succeeding phase. Daily calcium intake usually is increased with each phase. Thus the dietary concentrations of these nutrients are changed accordingly. The scientific validity of the phase feeding concept has not been established. Experimental results have failed to prove that a hen requires more nutrient per day at one stage of production than at another stage (Latshaw, 1981; Ousterhout, 1981; Sell et al., 1987). Relatively low levels of feed intake during early egg production, however, necessitate the use of high nutrient concentrations in diets during this phase of production. Egg Weight Egg weight is correlated with body weight of laying hens (Jull, 1924). The relative egg weight during a laying cycle parallels the relative body weight. Within a flock, heavier birds lay heavier eggs (Leeson and Summers, 1987a). A body weight decline in summer may account for the production of smaller eggs during that season (Cunningham et al., 1960). Nutritional means may be used to alter egg weight slightly. Early in the egg production cycle, the objective would be to increase egg weight. In one study (Summers and Leeson, 1983), the weight of eggs from pullets was not affected by increases in dietary levels of methionine, linoleic acid, or protein above the established requirement. Another study showed that increasing the level of dietary linoleic acid from 0.6 percent to 4.3 percent increased by egg weight during the first 14 weeks of production; however, average daily egg yield was not affected (March and MacMillan, 1990). In a different study, adding 3 or 6 percent fat to diets fed during early

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 egg production increased egg weight by increasing yolk weight whether the diets were isocaloric or nonisocaloric (Sell et al., 1987). When egg weight is increased by fat supplementation of diets, it is not known if the response is due to fat in general or is a specific response to linoleic acid (Whitehead, 1981; Balnave, 1982; Scragg et al., 1987). Increasing the percentage of fat or oil in isoenergetic diets caused hens to lay heavier eggs (Whitehead, 1981; Sell et al., 1987). Decreasing the dietary energy level, as may occur when sorghum or barley is substituted for corn, may decrease egg weight (Coon et al., 1988). Diet costs may increase when supplemental fats are used to obtain higher dietary fat and energy concentrations. Thus managers should determine the economic effectiveness of increasing egg weight in this way. Older laying hens produce a high proportion of extralarge eggs for which monetary returns often do not offset costs of production. Thus, a goal of feed formulators may be to reduce the weight of eggs produced by older hens. Decreasing dietary levels of the most limiting amino acid can affect egg weight (Morris and Gous, 1988). For example, weight of eggs produced by hens more than 38 weeks of age was reduced by limiting methionine intake to 270 mg per hen daily, compared with feeding 300 mg methionine per hen daily (Peterson et al., 1983). A review of 12 scientific papers indicated that as the most limiting amino acid level decreased below the required level, egg weight and rate of egg production were proportionally reduced. This reduction occurred until egg weight decreased to about 90 percent of maximum. Further decreases in the amino acid level decreased only the rate of egg production. An exception to the general effects of amino acid adequacy and egg weight occurs with tryptophan, whereby a deficiency of this amino acid failed to decrease egg weight (Jensen et al., 1990). MINERALS AND VITAMINS Mineral requirements of egg-type chickens in production are similar to mineral requirements of other poultry, with the exception of calcium. The onset of egg production creates a need for more calcium to make the eggshell. A question arises about the best time to switch pullets from a low-calcium growing diet to a high-calcium laying diet. Feeding a diet with 3.25 percent calcium starting at 50 days of age increased the incidence of urolithiasis in later life (Wideman et al., 1985). Changing from a low- to a high-calcium diet at 14 weeks of age or later, however, caused no detrimental effects on performance through 60 weeks (Keshavarz, 1987). Although high-calcium levels are detrimental when fed early in a pullet's life, feeding high-calcium levels several weeks before the onset of egg production seems to do no harm. The calcium requirement listed in Table 2-3 is similar to values listed in earlier editions. Definitive research is still lacking regarding several questions, however. Tests that cover a whole production cycle and that provide increments of calcium ranging from 3 to 4.5 g per hen daily would be helpful. Such tests would answer questions related to amounts of calcium needed, especially for the maintenance of eggshell strength in older layers. Conditions under which larger-particle-size calcium sources consistently improve eggshell strength should also be identified. Levels of nutrients other than calcium may also affect eggshell strength. A wide sodium-to-chloride ratio can increase blood pH and bicarbonate concentrations (Cohen et al., 1972). These increases may be the mechanism by which eggshell strength is improved at thermoneutral zone temperatures with some diets when sodium chloride is replaced by sodium bicarbonate in the water (Frank and Burger, 1965) or feed (Miles and Harms, 1982; Makled and Charles, 1987). Phosphorus levels may also affect eggshell strength. Excess dietary phosphorus may decrease eggshell strength (Arscott et al., 1962; Miles and Harms, 1982). The amount of phosphorus needed each day (Table 2-3) has been decreased from amounts recommended in earlier editions. A daily intake of 250 mg of nonphytate phosphorus should be adequate for normal production and health. Although feeding diets containing excess phosphorus is generally undesirable, poultry encountering heat stress may require additional phosphorus. Garlich et al. (1978) and McCormick et al. (1980) reported that chickens fed diets containing relatively high phosphorus levels were more tolerant of high ambient temperatures than were those fed normal phosphorus levels. The use of dietary phosphorus at requirement levels should result in less phosphorus in excreta. This fact may assume more importance in the future if manure application rates to land are determined on the basis of phosphorus content. Research information published about vitamin requirements does not indicate the need for any major change in recommendations from the previous edition. However, results from several reports showed that, for maximum egg yield, the choline requirement was about 1,050 mg per hen daily (Parsons and Leeper, 1984; Keshavarz and Austic, 1985; Miles et al., 1986). Therefore the choline requirement for laying hens has been increased. BROWN-EGG-LAYING LAYERS Estimated nutrient requirements of brown-egg layers are listed in Table 2-3. Because little research has been

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 done with brown-egg-laying layers, the committee had little quantitative information to review for establishing nutrient requirements. Estimates of daily requirements given in Table 2-3 are listed as 10 percent greater than those of the white-egg-laying layers. The 10 percent increase is justified on the basis that brown-egg-laying layers have heavier body weights and generally produce more egg mass per hen daily. Egg-Type Breeders Nutrient requirements for egg-type breeders are listed in Table 2-3. Major nutrient requirements are the same for producing an egg for human consumption as for producing an egg for hatching; however, dietary levels of trace minerals and vitamins that result in maximum egg yield per day may be too low for the developing embryo (Naber, 1979). Vitamin and trace mineral levels in the egg can be increased by increasing the dietary levels. Higher riboflavin, pantothenic acid, and vitamin B12 levels are especially critical for maximum hatchability, although several other nutrients may also become limiting. As a result, several of the micronutrient requirements are higher in breeding diets than in laying diets. MOLTING HENS After 8 to 12 months of egg production, some flocks are molted as a means of extending the period of production (Zimmerman and Andrews, 1987). A combination of feed, water, and light restriction is usually used to stop egg production and cause a rest, which may last from 3 to 6 weeks. A rest can also be induced by free-choice feeding of a diet containing a deficiency or excess of a specific nutrient. Examples of nutrients used to induce molt include excess iodine (Arrington et al., 1967), excess zinc (Supplee et al., 1961), and sodium chloride deficiency (Whitehead TABLE 2-5 Typical Body Weights, Feed Requirements, and Energy Consumption of Broilers Age (weeks) Body Weight (g) Weekly Feed Consumption (g) Cumulative Feed Consumption (g) Weekly Energy Consumption (kcal ME/bird) Cumulative Energy Consumption (kcal ME/bird)   Male Female Male Female Male Female Male Female Male Female 1 152 144 135 131 135 131 432 419 432 419 2 376 344 290 273 425 404 928 874 1,360 1,293 3 686 617 487 444 912 848 1,558 1,422 2,918 2,715 4 1,085 965 704 642 1,616 1,490 2,256 2,056 5,174 4,771 5 1,576 1,344 960 738 2,576 2,228 3,075 2,519 8,249 7,290 6 2,088 1,741 1,141 1,001 3,717 3,229 3,651 3,045 11,900 10,335 7 2,590 2,134 1,281 1,081 4,998 4,310 4,102 3,459 16,002 13,794 8 3,077 2,506 1,432 1,165 6,430 5,475 4,585 3,728 20,587 17,522 9 3,551 2,842 1,577 1,246 8,007 6,721 5,049 3,986 25,636 21,508 NOTE: Values are typical for broilers fed well-balanced diets providing 3,200 kcal ME/kg. and Shannon, 1974; Naber et al., 1984). After the rest, egg production can be initiated by stimulatory lighting. Little research information is available on the nutrient requirements of molted hens; therefore the committee has assumed that requirements are similar to those of hens during the first cycle of production. MEAT-TYPE CHICKENS Dietary requirements for meat-type chickens vary according to whether the birds are broilers being started and grown for market, broiler breeder pullets and hens, or broiler breeder males. Starting and Growing Market Broilers Chickens of broiler strains have been selected for rapid weight gain and efficient utilization of feed. Broilers are usually allowed to feed on an ad libitum basis to ensure rapid development to market size, although some interest has been expressed in controlling feed intake in an attempt to minimize the development of excessive carcass fat. Broilers are marketed at a wide range of ages and body weights (Table 2-5). Females may be grown to 900- to 1,000-g body weight to supply Cornish hens, mixed sexes may be reared to 1.8 to 2 kg for use as whole birds and specialty parts, and males may be grown to 2.8 to 3 kg for deboned meat. Thus it is difficult to establish a single set of requirements that is appropriate to all types of broiler production. Furthermore, nutrient requirements may vary according to the criterion of adequacy. In the instance of essential amino acids, greater dietary concentrations may be required to optimize efficiency of feed utilization than would be needed to maximize weight gain. There also is evidence that the dietary requirement for lysine to maximize yields of breast meat of broilers is greater than that needed to

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 maximize weight gain (Acar et al., 1991) and that differences exist among strains of broilers with respect to this need for more lysine (Bilgili et al., 1992). Expression of a requirement for any nutrient is relative, and many factors must be considered. Many nutrients are interdependent, and it is difficult to express requirements for one without consideration of the quantity of the other. Examples include the relationships that exist between lysine and arginine and among calcium, phosphorus, and vitamin D3 levels in the diet. Other factors that may affect requirements include age and gender of the animal. Some studies suggest that males require greater quantities of nutrients than do females at a similar age; however, when expressed as a percentage of the diet, there seems to be little difference in nutrient requirements of the sexes. The requirements for many nutrients seem to diminish with age, but for most nutrients there have been few research studies designed to precisely estimate requirements for all age periods, especially for those beyond 3 weeks of age. Any expression of nutrient requirements can be only a guideline representing a consensus of research reports. These guidelines must be adjusted as necessary to fit the wide variety of ages, sexes, and strains of broiler chickens. The values given in Table 2-6 are generally minimum levels that satisfy general productive activities and(or) prevent deficiency syndromes. Requirements are presented for specific age periods. These age periods are based on the chronology for which research data were available. These nutrient requirements are often implemented for younger age intervals or on a weight-of-feed consumed basis. Where information is lacking, bold italicized values represent an estimate based on values attained for other ages or related species. The data from the peer-reviewed scientific literature that serve as a basis for the committee's estimation of nutrient requirements are presented in Appendix Table A-3a. AMINO ACIDS Relatively high concentrations of dietary amino acids are needed to support the rapid growth of meat-type chickens. Body weights of commercial meat-type chickens will increase 50- to 55-fold by 6 weeks after hatching. A large part of this increase in weight is tissue of substantial protein content. Thus, adequate amino acid nutrition is vital to the successful feeding program for this type of chicken. Methionine plus Cystine The greatest disagreement concerning amino acid requirements for broilers centers on the sulfur amino acids, methionine and cystine. In TABLE 2-6 Nutrient Requirements of Broilers as Percentages or Units per Kilogram of Diet (90 percent dry matter) Nutrient Unit 0 to 3 Weeksa; 3,200b 3 to 6 Weeksa; 3,200b 6 to 8 Weeksa; 3,200b Protein and amino acids Crude proteinc % 23.00 20.00 18.00 Arginine % 1.25 1.10 1.00 Glycine + serine % 1.25 1.14 0.97 Histidine % 0.35 0.32 0.27 Isoleucine % 0.80 0.73 0.62 Leucine % 1.20 1.09 0.93 Lysine % 1.10 1.00 0.85 Methionine % 0.50 0.38 0.32 Methionine + cystine % 0.90 0.72 0.60 Phenylalanine % 0.72 0.65 0.56 Phenylalanine + tyrosine % 1.34 1.22 1.04 Proline % 0.60 0.55 0.46 Threonine % 0.80 0.74 0.68 Tryptophan % 0.20 0.18 0.16 Valine % 0.90 0.82 0.70 Fat Linoleic acid % 1.00 1.00 1.00 Macrominerals Calciumd % 1.00 0.90 0.80 Chlorine % 0.20 0.15 0.12 Magnesium mg 600 600 600 Nonphytate phosphorus % 0.45 0.35 0.30 Potassium % 0.30 0.30 0.30 Sodium % 0.20 0.15 0.12 Trace minerals Copper mg 8 8 8 Iodine mg 0.35 0.35 0.35 Iron mg 80 80 80 Manganese mg 60 60 60 Selenium mg 0.15 0.15 0.15 Zinc mg 40 40 40 Fat soluble vitamins A IU 1,500 1,500 1,500 D3 ICU 200 200 200 E IU 10 10 10 K mg 0.50 0.50 0.50 Water soluble vitamins B12 mg 0.01 0.01 0.007 Biotin mg 0.15 0.15 0.12 Choline mg 1,300 1,000 750 Folacin mg 0.55 0.55 0.50 Niacin mg 35 30 25 Pantothenic acid mg 10 10 10 Pyridoxine mg 3.5 3.5 3.0 Riboflavin mg 3.6 3.6 3 Thiamin mg 1.80 1.80 1.80 NOTE: Where experimental data are lacking, values typeset in bold italics represent an estimate based on values obtained for other ages or related species. a The 0- to 3-, 3- to 6-, and 6- to 8-week intervals for nutrient requirements are based on chronology for which research data were available; however, these nutrient requirements are often implemented at younger age intervals or on a weight-of-feed consumed basis. b These are typical dietary energy concentrations, expressed in kcal MEn/kg diet. Different energy values may be appropriate depending on local ingredient prices and availability. c Broiler chickens do not have a requirement for crude protein per se. There, however, should be sufficient crude protein to ensure an adequate nitrogen supply for synthesis of nonessential amino acids. Suggested requirements for crude protein are typical of those derived with corn-soybean meal diets, and levels can be reduced when synthetic amino acids are used. d The calcium requirement may be increased when diets contain high levels of phytate phosphorus (Nelson, 1984).

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 part, this is because most studies are not designed to determine both the requirements of methionine per se and the requirement for the combined quantity of methionine and cystine. Many attempts have been made, especially with purified diets, to ascertain the relative proportions needed of these two amino acids, with variable results. Many have attributed a share of the disagreement in estimated requirements to factors such as the sparing effects of choline (Quillen et al., 1961; Pesti et al., 1979) or sulfate (Gordon and Sizer, 1955; Ross and Harms, 1970) or the negative effects of copper sulfate (Baker and Robbins, 1979). It is unfortunate that although a number of studies have been carried out to examine the effects of different dietary variables on the requirement for methionine, few of these actually made attempts to estimate an overall requirement value. Although calculations can be made in some instances, these do not have the statistical basis that values derived from the original data would have had. Another factor that may contribute to the disagreement in results is the comparison of results using crystalline amino acid diets with results using diets based on practical ingredients, primarily corn and soybean meal. Although this difference may relate in part to the incomplete digestion of the protein in the intact ingredients, most recent digestibility studies suggest that amino acids in corn and soybean meal are well digested, on the order of 85 percent or more. Differences in digestibility of practical and semipurified diets are, therefore, not of sufficient magnitude to account for the major differences that seem to occur between these types of diets. The cystine status of the basal diet is a major factor that contributes to the apparent disagreement in results, especially when diets with intact ingredients are used. Generally, a basal diet, considered deficient in sulfur amino acids, is supplemented with graded levels of methionine and the response determined. The point of maximum response is then noted, and the sum of dietary plus supplemental methionine is added to the dietary cystine content to arrive at the need for total sulfur amino acids (TSAA). However, this procedure assumes that the basal diet does not contain a surfeit of cystine. Therefore one must determine whether or not the basal diet is adequate or excessive in cystine before combining these values for a total TSAA estimate. Total dietary cystine levels can be influenced by dietary protein levels, choice of protein-contributing ingredients, and use of supplemental amino acids. Unfortunately, the majority of the reports estimate TSAA requirements and do not attempt to differentiate between needs for methionine and needs for TSAA. For methionine per se, there is minimal research on which to base changes in the recommendation of 0.5 percent made in the previous edition. Of the reports in the literature for methionine requirements for the period from 0 to 21 days, two (Waldroup et al., 1979; Tillman and Pesti, 1985) are above the NRC (1984) recommendation, four (Dean and Scott, 1965; Robbins and Baker, 1980a; Moran, 1981; Thomas et al., 1985) are at or near that recommendation, and two (Klain et al., 1960; Hewitt and Lewis, 1972) are considerably below. For the period of 3 to 6 or 6 to 8 weeks, there is even less work on the requirements for methionine per se. The report of Moran (1981) plus estimates from a computer model (Hurwitz et al., 1978) would support retaining the previously recommended value until sufficient research has been conducted to support its modification. Even greater diversity exists among estimates for TSAA requirements, as would be expected from the factors indicated above. Evaluation of results obtained from feeding crystalline amino acid diets certainly suggests a markedly lower TSAA value (Klain et al., 1960; Dean and Scott, 1965; Graber et al., 1971; Robbins and Baker, 1980a; Willis and Baker, 1980, 1981a; Baker et al., 1983). Although basing TSAA requirements on data using crystalline amino acids is perhaps not justifiable for practical diets, it does point out that the TSAA requirement could be less if a proper balance between available methionine and cystine existed. In evaluating results from birds fed diets with intact ingredients, one can find values that support the change in recommended TSAA requirements for 0 to 3 weeks of age from 0.93 to 0.87 percent of the diet (Nelson et al., 1960; Hewitt and Lewis, 1972; Boomgaardt and Baker, 1973b,c; Woodham and Deans, 1975; Attia and Latshaw, 1979; Robbins and Baker, 1980a,b; Wheeler and Latshaw, 1981; Baker et al., 1983; Mitchell and Robbins, 1983; Thomas et al., 1985). In many of these studies, diets were supplemented with lysine, which permitted a lower protein level and reduced cystine content; therefore a surfeit of cystine was less likely to exist in these studies. Research is needed using practical ingredients to evaluate the separate needs for methionine and cystine in such diets. For the 3- to 6-week period, most reports are in agreement with the previous recommendation (Graber et al., 1971; Holsheimer, 1981; Wheeler and Latshaw, 1981; Mitchell and Robbins, 1983). Two reports (Jensen et al., 1989; Mendonca and Jensen, 1989a) suggested a higher value, based in part on reduction in carcass fat content. There is minimal research on the TSAA needs from 6 to 8 weeks of age and little justification for change in the previous recommendation. More research is needed to delineate the separate needs for methionine and cystine in diets consisting of practical ingredients. This research may eliminate much of the current disagreement regarding TSAA needs of the broiler.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 Arginine The committee has made significant changes in its recommendation for the arginine requirements of broilers. It has eliminated from consideration all studies in which potential lysine:arginine antagonisms existed because such antagonisms are unlikely to occur with practical ingredients. Recommended requirements have been reduced to 1.25 and 1.1 percent for the 0-to 3- and 3- to 6- week growth periods, respectively. Lysine The requirement of broilers from 0 to 3 weeks of age has been reduced from 1.2 to 1.1 percent of the diet. There has been little recent research on the requirements for this amino acid, but evaluation of previous research supports this reduction (Edwards et al., 1956; Boomgaardt and Baker, 1973a,b; Woodham and Deans, 1975; McNaughton et al., 1978; Burton and Waldroup, 1979). There is a dearth of published recommendations for the period from 3 to 6 weeks of age. Limited research, however, supports the previous recommendation (Holsheimer, 1981). Research results for the period from 6 to 8 weeks are inconclusive. Some work suggests that the previous requirement is low (Bornstein, 1970; Boomgaardt and Baker, 1973b), whereas other studies suggest that it is high (Chung et al., 1973; Twining et al., 1973; Thomas et al., 1977). Therefore, the previous requirement of 0.85 percent was not changed. Tryptophan The committee has reduced the requirement for this amino acid from 0.23 to 0.2 percent for the broiler 0 to 3 weeks of age on the basis of its evaluation of published reports from many sources (Wilkening et al., 1947; Griminger et al., 1956; Klain et al., 1960; Boomgaardt and Baker, 1971; Hewitt and Lewis, 1972; Woodham and Deans, 1975; Steinhart and Kirchgessner, 1984; Smith and Waldroup, 1988a). Minimal research has been conducted on tryptophan requirements of the broiler at more than 3 weeks. Estimates from computer modeling (Hurwitz et al., 1978) suggest that lower levels of tryptophan may be required during this period, but these estimates have not been rigorously examined. Threonine Considerable work has been conducted on the threonine requirement for broiler chickens in recent years. The majority of the studies support the present recommended value of 0.8 percent for broilers at 0 to 3 weeks of age (Uzu, 1986; Robbins, 1987; Thomas et al., 1987; Bertram et al., 1988; Smith and Waldroup, 1988b; Austic and Rangel-Lugo, 1989). Little research has been done on threonine requirements for broilers older than 3 weeks of age. Isoleucine, Leucine, Valine, Phenylalanine, Phenylalanine plus Tyrosine, Glycine plus Serine, Histidine, and Proline Sufficient studies with intact protein diets have been conducted to allow estimation of the requirements for leucine, isoleucine, and valine during the 0-to 3-week period (Almquist, 1947; D'Mello, 1974; Woodham and Deans, 1975; Thomas et al., 1988). Only a few studies with intact protein diets have been conducted for phenylalanine or phenylalanine plus tyrosine (Almquist, 1947; Woodham and Deans, 1975) and for glycine plus serine (Ngo and Coon, 1976) during the period from 0 to 3 weeks. Therefore the committee considered studies with purified diets (Fisher et al., 1957; Klain et al., 1960; Dean and Scott, 1965; Sasse and Baker, 1972; Coon et al., 1974; Baker et al., 1979) in estimating these requirements. The reported values for phenylalanine plus tyrosine and glycine plus serine vary greatly among studies, particularly in the latter instance. The histidine requirement for the period from 0 to 3 weeks is based primarily on purified diet studies (Klain et al., 1960; Dean and Scott, 1965; Baker et al., 1979). Although proline is not usually considered to be an essential amino acid for poultry, research has shown that young chicks may not synthesize sufficient proline to meet their requirements (Greene et al., 1962; Graber et al., 1970); thus, a dietary source of proline must be provided. The committee found no published research data for this group of amino acids for the periods from 3 to 6 and 6 to 8 weeks, although the study by Mendonca and Jensen (1989b) suggested that the valine requirement for 3 to 6 weeks exceeds 0.70 percent. Since the lysine requirements for these growth periods are documented, the requirements for this group of amino acids for the periods from 3 to 6 and 6 to 8 weeks have been estimated from the lysine values by using the amino acid:lysine ratio for the period from 0 to 3 weeks. Thus the committee assumed that the ratios or patterns between these amino acids and lysine are relatively consistent throughout the growth stages. MINERALS The extent of research conducted on different minerals and vitamins is often in direct proportion to their economic value or to the likelihood of encountering a dietary deficiency in practical diets. Thus there is a great deal of literature concerning the calcium and phosphorus requirements of the broiler and minimal research concerning requirements for trace elements. The precise requirements for minerals such as potassium, magnesium, and iron in practical diets are not well defined because practical diets are usually adequate or only slightly deficient in these minerals. The requirements for minerals such as iron, manganese, and zinc are much lower for chicks fed semipurified diets containing little or no phytate and fiber than for those fed

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 practical diets, mainly because of relatively poor bioavailability of some minerals in practical ingredients (Kratzer and Vohra, 1986). For example, the bioavailability of manganese is very low in most practical feedstuffs, and there is evidence that practical ingredients reduce the bioavailability of inorganic dietary manganese (Halpin and Baker, 1986). The bioavailability of minerals in inorganic mineral supplements also varies greatly. For example, the bioavailability of zinc in zinc sulfate is much higher than in zinc oxide (Wedekind and Baker, 1990). Consequently, the reported requirement for a mineral may vary among studies owing to differences in the bioavailability of the supplemental mineral source and the use of ingredients that interfere with utilization of the mineral under study. Although substantial research has been conducted for most vitamins, the requirements for practical diets are not well defined. Practical diets are not markedly deficient in some vitamins. Consequently, several of the vitamin requirements are extrapolated from studies with purified or semipurified diets. The dietary levels needed to maximize some parameters may be higher than those needed to maximize growth. Examples of the latter include vitamin D3 levels for maximum tibia ash (Waldroup et al., 1963a; Lofton and Soares, 1986), vitamin E levels for maximum immune response (Tengerdy and Nockels, 1973; Colnago et al., 1984), and riboflavin levels for prevention of leg paralysis (Ruiz and Harms, 1988a). It is generally assumed that vitamin requirements decrease with increasing age, although this relationship is not well documented with the exception of choline in purified diets. Calcium and Phosphorus No changes have been made in the previously recommended calcium requirement of the broiler chick. Requirements for phosphorus are expressed in terms of nonphytate phosphorus. The nonphytate phosphorus requirement for the chick at 0 to 3 weeks of age remains unchanged; however, recommended values for 3 to 6 and 6 to 8 weeks have been reduced on the basis of studies by O'Rourke et al. (1952), Waldroup et al. (1963b, 1974a), Twining et al. (1965), Sauveur (1978), Yoshida and Hoshii (1982a), and Tortuero and Diez Tardon (1983). Potassium, Sodium, and Chlorine A reduction has been made in the potassium requirement of the broiler. The potassium requirement of broilers fed a semipurified diet seems to be between 0.25 and 0.30 percent (Leach et al., 1959). The requirement for broilers fed a practical diet is not documented. The requirements for sodium and chlorine have been increased for the period from 0 to 3 weeks on the basis of recent studies. The requirements for these minerals seem to decrease with increasing age (Hurwitz et al., 1973; Edwards, 1984). The research of Edwards (1984) has justified a reduction in the levels of sodium and chlorine recommended for broilers at 6 to 8 weeks of age. Magnesium The reported requirement varies among studies. Part of this variation may be due to the calcium and phosphorus content of the diet. Although type of diet varies among studies, there does not seem to be a consistent relationship between diet type and the reported magnesium requirement. After 3 weeks of age, the values suggested by the committee are only estimates. Iron and Copper Although only a few studies have been conducted on iron requirements of broilers, the results are consistent and indicate that the requirement is approximately 80 mg/kg (Davis et al., 1968; McNaughton and Day, 1979). Southern and Baker (1982) report that the requirement was only 40 mg/kg for chicks fed a dextrose-casein diet. The copper requirement of 8 mg/kg is based on the study of McNaughton and Day (1979). The committee suggests only estimated values after 3 weeks of age. Manganese Values given for chicks of all ages show wide differences in requirements depending on the type of diet used. The requirement reported for chicks fed a semipurified dextrose-casein diet (14 mg/kg; Southern and Baker, 1983a) is much lower than that of chicks fed a diet containing practical ingredients (50 mg/kg/ Gallup and Norris, 1939a,b). Zinc The zinc requirement of the young broiler is approximately 35 to 40 mg/kg in semipurified diets containing isolated soy protein or casein (Morrison and Sarett, 1958; O'Dell et al., 1958; Roberson and Shaible, 1958). Studies on corn-soybean meal and sesame meal diets suggest that the requirement is in excess of 40 mg/kg (Edwards et al., 1959; Lease et al., 1960; Zeigler et al., 1961). This conclusion was based primarily on small growth responses to zinc supplementation of the basal diets. The estimated zinc requirement is somewhat tenuous, because the estimate was based on calculated values for zinc content of the feed ingredients. Recent work by Wedekind et al. (1990) showed that the tibia zinc concentration of chicks fed a corn-soybean meal diet was increased markedly by dietary zinc supplementation but did not provide an estimate of requirements. The source of supplemental zinc used in most of the cited studies was zinc sulfate or zinc chloride. Availability of zinc varies among sources (Wedekind and Baker, 1990). In a diet containing egg white as the primary protein source, the requirement for zinc is only 14 to 18 mg/kg (Southern and Baker, 1983b; Dewar and Downie, 1984). Only tentative values are given for chicks after 3 weeks of age.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 Iodine Little research has been conducted to establish the iodine requirement of the broiler chick. The present requirement is based on the study by Creek et al. (1957). Selenium No changes have been made in the recommended dietary selenium concentrations for broiler chickens. A concentration of 0.15 mg selenium per kilogram of diet is recommended (Jensen et al., 1986). VITAMINS Vitamin A Tentative requirement values have been listed for all ages. The requirement estimates vary from 900 to 2,200 IU/kg among studies. Requirement values from more recent studies are lower than those from earlier ones. Vitamin D The requirement estimates for maximum growth are consistent among most studies. The requirement for maximum tibia ash, however, may be higher than that for growth (Waldroup et al., 1965; Lofton and Soares, 1986). Vitamin E Tentative values have been expressed for all ages. The results of the few studies conducted are variable. The requirement for prevention of encephalomalacia may be higher than that for growth only (Singsen et al., 1955). In addition, the requirement for maximum immune response may be much higher than that for growth (Tengerdy and Nockels, 1973; Colnago et al., 1984). Vitamin K The vitamin K requirements of the broiler are unchanged. The requirement is estimated at approximately 0.5 mg/kg for chicks fed glucose-isolated soy protein diets (Nelson and Norris, 1960, 1961b). Riboflavin The riboflavin requirements for broilers at 0 to 3 and 3 to 6 weeks of age (3.6 mg/kg of diet) are unchanged. Most studies indicate that the riboflavin requirement is 2.5 to 3.5 mg/kg. Several studies have indicated that the requirement for prevention of leg paralysis is higher than that for growth (Ruiz and Harms, 1988c). Pantothenic Acid Tentative requirements have been expressed for broilers of all ages. Little work has been done, and there is no good basis for the requirement in practical diets. The requirement is 5 mg/kg in a purified diet, and thus twice this level should be adequate for practical diets to compensate for potentially limited availability of pantothenic acid from the ingredients. Bauernfeind et al. (1942) reported that 7.5 to 10 mg of pantothenic acid per kilogram of diet was adequate for Leghorn chicks and that practical diets normally contain sufficient levels of this vitamin. Jukes and McElroy (1943) also reported a pantothenic acid requirement of 10 mg/kg of diet. Niacin The niacin requirement has been increased for broilers of all ages (see Table 2-5). Requirement estimates vary from 22 to greater than 55 mg/kg among studies using intact protein diets, with most estimates being in the range of approximately 25 to 35 mg/kg. The requirement is somewhat lower for purified diets (Ruiz and Harms, 1988a; 1990). Vitamin B12 Few requirement studies have been conducted. The requirement seems to be approximately 0.01 mg/kg (Looi and Renner, 1974; Rys and Koreleski, 1974). Choline No changes have been made in the choline requirement of the broiler at 0 to 3 weeks of age, and tentative requirements are given for broilers at 3 to 6 and 6 to 8 weeks. Many studies have been conducted on choline requirements, and the requirement estimates are highly variable. Choline requirements are influenced by protein and sulfur amino acid content of the diet and by age of broilers. The requirements listed in Table 2-5 should be sufficient for practical diets containing adequate levels of methionine and cystine. The choline requirement is much lower and decreases markedly with increasing age for chicks fed purified diets (Molitoris and Baker, 1976; Lowry et al., 1987). A decrease in choline requirement with age has not been documented when practical diets are fed. Requirement values for broilers from 3 to 6 and 6 to 8 weeks, however, have been extrapolated from studies that used purified diets (Gardiner and Dewar, 1976; Molitoris and Baker, 1976; Lowry et al., 1987). Biotin No changes have been made in the biotin requirement of the broiler to 6 weeks of age, with a tentative requirement expressed for 6 to 8 weeks. Estimates from most studies indicate that the requirement is between 0.15 and 0.20 mg/kg. Folic Acid No changes have been made in the folic acid requirement of the broiler at 0 to 3 and 3 to 6 weeks of age, with tentative requirements expressed for 6 to 8 weeks. Requirement values vary among studies. Recent studies, however, indicate that the requirement is between 0.35 and 0.50 mg/kg when determined with semipurified diets. Thus the requirement is probably higher when birds are fed practical diets. Thiamin Tentative requirements are expressed for broilers of all ages. There is little research with broilers on which to base a requirement. The requirement seems to

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 be relatively low, and practical diets normally contain levels well in excess of the estimated requirements. Pyridoxine The pyridoxine requirement has been increased for broilers of all ages, with a tentative requirement given for broilers at 6 to 8 weeks of age. Many studies have been conducted, with requirement estimates ranging from 2.3 to 3.5 mg/kg for intact protein diets. The requirement seems to be only approximately 1.0 mg/kg for a purified diet (Lee et al., 1976; Yen et al., 1976). The pyridoxine requirement, however, increases with an increase in dietary protein level (Gries and Scott, 1972a; Daghir and Shah, 1973). ESSENTIAL FATTY ACID Linoleic Acid The linoleic acid requirement has been estimated as 1.0 percent of the diet (Balnave, 1970). Broiler Breeder Pullets and Hens Meat-type breeder hens will become obese if allowed ad libitum consumption of feed; therefore some form of nutrient limitation must be practiced. Most research has focused on feeding systems, with some form of quantitative restriction of intake generally practiced to maintain body weights within guidelines suggested by the breeder. Early research suggested that feeding bulky, high-fiber diets would successfully limit MEn intake (Milby and Sherwood, 1953; Singsen et al., 1959; Isaacks et al., 1960; Summers et al., 1967; Fuller et al., 1973), but more recent studies indicate that modern broiler strains can consume large volumes of feed, a capability that makes this method impractical as a means of controlling weight (Waldroup et al., 1976a). Other studies have suggested that low-protein diets (Waldroup et al., 1966), diets low in specific amino acids (Singsen et al., 1964), or diets imbalanced in amino acids (Couch and Abbott, 1974) might control body weight when offered for ad libitum consumption, but such diets have not been readily accepted in commercial practice because of large variability in bird response. Little research has been conducted to determine the specific nutrient requirements of meat-type females from hatch to maturity. Powell and Gehle (1975) estimated the tryptophan requirement of growing broiler breeder pullets; this seems to be the lone estimate of protein or amino acid needs during this age period. Harms (1980) and Harms and Wilson (1987) have suggested requirements for the growing pullet, but these have not been subjected to rigid evaluation. Therefore there is not sufficient research data on which to base suggested requirements for the growing and developing broiler breeder meat-type pullet at this time. Nutrient requirement data presented in Table 2-7 for the broiler breeder meat-type hen are limited to those for which some documentation is available. PROTEIN AND AMINO ACIDS Chickens do not require a specific level of crude protein per se; rather, they have a requirement for specific amino acids plus sufficient protein to supply either the nonessential amino acids themselves or amino nitrogen for their synthesis. In the instance of meat-type breeder hens, there is a paucity of research directed toward determining specific requirements for essential amino acids. Therefore a minimum crude protein intake is generally designated to provide adequate amounts of essential amino acids whose requirements are not adequately known. Daily crude protein intakes of 18 to 20 g per hen seem adequate, assuming that essential amino acid needs are met (Waldroup et al., 1976b; Pearson and Herron, 1981; Spratt and Leeson, 1987), although more abundant levels (up to 23 g/day) may be needed during periods of highest productivity to achieve maximum egg mass yield (Jeroch et al., 1982; Schloffel et al., 1988). Because the size of the TABLE 2-7 Nutrient Requirements of Meat-Type Hens for Breeding Purposes as Units per Hen per Day (90 percent dry matter) Nutrient Unit Requirements Protein and amino acids Proteina g 19.5 Arginine mg 1,110 Histidine mg 205 Isoleucine mg 850 Leucine mg 1,250 Lysine mg 765 Methionine mg 450 Methionine + cystine mg 700 Phenylalanine mg 610 Phenylalanine + tyrosine mg 1,112 Threonine mg 720 Tryptophan mg 190 Valine mg 750 Minerals Calcium g 4.0 Chloride mg 185 Nonphytate phosphorus mg 350 Sodium mg 150 Vitamin Biotin µg 16 NOTE: These are requirements for hens at peak production. Broiler breeder hens are usually fed on a controlled basis to maintain body weight within breeder guidelines. Daily energy consumption varies with age, stage of production, and environmental temperature but usually ranges between 400 and 450 ME kcal per hen at peak production. For nutrients not listed, see requirements for egg-type breeders (Table 2-3) as a guide. Where experimental data are lacking, values typeset in bold italics represent an estimate based on values obtained for other ages or related species. a Broilers do not have a requirement for crude protein per se. There, however, should be sufficient crude protein to ensure an adequate nitrogen supply for synthesis of nonessential amino acids. Suggested requirements for crude protein are typical of those derived with corn-soybean meal diets, and levels can be reduced somewhat when synthetic amino acids are used.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 egg has a significant effect on the initial weight of the chick and its subsequent performance (Gardiner, 1973; Guill and Washburn, 1973; Proudfoot and Hulan, 1981), maximum egg weight during early production is an important economic factor. The protein requirement for dwarf breeder hens does not exceed 13.6 percent of the diet (Larbier et al., 1979). Excessive crude protein intakes are to be avoided. Daily intakes of 27 g per hen had adverse effects on hatchability (Pearson and Herron, 1981, 1982). Lower crude protein intakes may be satisfactory if additional amino acid supplementation is practiced. Bornstein et al. (1979) calculated that a daily crude protein intake of 15.6 to 16.5 g per hen would be sufficient in terms of an ideal amino acid mixture. Performance of hens fed corn-soybean meal diets providing 16 g protein per day was not improved by supplemental lysine and methionine (Waldroup et al., 1976b). Few trials have been conducted to determine specific amino acid requirements. Harms and Wilson (1980) reported a daily requirement for methionine of between 400 and 478 mg; 400 mg per day gave performance statistically equivalent to that at higher levels of intake. Halle et al. (1984), using nitrogen balance studies, indicated a TSAA need of 694 mg per day. For dwarf (dw) hens, Guillaume (1977) estimated daily methionine and lysine needs of 360 to 380 and 750 mg per hen, respectively. Wilson and Harms (1984) obtained satisfactory performance with average daily intakes per hen of 682 mg of TSAA, 808 mg of lysine, 1,226 mg of arginine, and 223 mg of tryptophan, with 18.6 g of crude protein per day. Using various prediction models or equations, several workers have estimated amino acid requirements (Waldroup and Hazen, 1976; Waldroup et al., 1976c; Scott, 1977; Bornstein et al., 1979). In the study by Bornstein et al. (1979), hens fed diets formulated to meet these requirements on the basis of prediction models performed as well as those fed diets formulated in the conventional way. ENERGY Broiler breeder hens are usually fed on a controlled basis to maintain body weight within breeder guidelines. Daily energy consumption will vary with age, stage of production, and environmental temperature, but will usually range from 400 to 450 kcal ME per hen daily (Waldroup and Hazen, 1976; Waldroup et al., 1976a; Bornstein et al., 1979; Bornstein and Lev, 1982; Pearson and Herron, 1982; Spratt and Leeson, 1987; Spratt et al., 1990a,b). MINERALS AND VITAMINS Calcium Shell strength of eggs from meat-type hens increases as calcium level is increased (Mehring, 1965). Egg production and hatchability of meat-type hens on litter were not improved by feeding more than 3.91 g of calcium per hen daily (Wilson et al., 1980). One of the best determinants of calcium adequacy for breeder hens is egg specific gravity; eggs should have a specific gravity of 1.080 or greater for optimal hatchability (McDaniel et al., 1979). Since meat-type hens are usually given a daily allotment of feed early in the morning before significant eggshell calcification occurs, supplying a portion of the calcium in an afternoon feeding may improve eggshell quality (Farmer et al., 1983; Van Wambeke and DeGroote, 1986). Feeding the entire dietary allocation in the afternoon, however, may significantly reduce hatchability because of production of eggs with thicker eggshells (Brake, 1988). Phosphorus No significant differences in egg production, hatchability of fertile eggs, or specific gravity of eggs were noted in feeding from 532 to 1,244 mg total phosphorus per hen daily (163 to 863 mg nonphytate phosphorus per hen daily), although egg production was improved numerically by feeding 718 mg total phosphorus (338 mg nonphytate phosphorus) per day (Wilson et al., 1980). For both calcium and phosphorus, requirements for hens maintained in cages may be significantly greater than for hens on litter floors (Harms et al., 1961; Singsen et al., 1962; Harms et al., 1984). Sodium Egg production, feed efficiency, egg weight, fertility, and hatchability of meat-type breeder hens were not improved by feeding more than 154 mg of sodium per hen daily (Damron et al., 1983); sodium intakes in excess of 320 mg per day were shown to reduce fertility. Chlorine Harms and Wilson (1984) reported that 254 mg of chlorine per hen daily resulted in the best overall performance of meat-type broiler hens, as measured by egg production and hatchability. However, performance on this intake did not differ significantly from performance on intakes of 185 mg per day. Biotin The requirement for biotin by the meat-type hen has been estimated to be 16 µg per hen daily. The hen may be considered to be receiving adequate biotin if the yolk biotin concentration is at least 550 ng/g (Whitehead et al., 1985). Broiler Breeder Males Historically, meat-type breeder cockerels have been grown with the females. Because of recent changes in genetics and management practices, an increasing number of males are being grown or fed separately. Males maintained in floor pens with natural mating may be fed from a separate feeding system; males maintained in cages for artificial

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 insemination may be individually fed. The major advantage of separate feeding is control of body weight and its subsequent impact on fertility and mating ability. Thus a set of nutrient requirements for male meat-type breeders, although limited in scope, is listed in Table 2-8. It should be noted that diets intended for use by the breeder hen, when fed to control male body weight, appear to have no detrimental effects on male performance. PROTEIN Protein requirements of breeder cockerels have been evaluated during the growing and adult periods by using both White Leghorn and Meat-type cockerels. In studies with Single Comb White Leghorn (SCWL) cockerels, low crude protein levels fed during the grower period reduced body weights and delayed testicular development, but, on subsequent feeding of adequate protein, reproductive performance was not impaired (Wilson et al., 1965; Jones et al., 1967). Diets containing 12.4 percent crude protein offered for ad libitum consumption to broiler breeder males during the period of 7 to 21 weeks of age were adequate for development of the reproductive system and subsequent TABLE 2-8 Nutrient Requirements of Meat-Type Males for Breeding Purposes as Percentages or Units per Rooster per Day (90 percent dry matter)     Age (weeks)   Unit 0 to 4 4 to 20 20 to 60 Metabolizable energya kcal — — 350 to 400 Protein and amino acids Proteinb % 15.00 12.00 — Lysinec % 0.79 0.64 — Methioninec % 0.36 0.31 — Methionine + cystinec % 0.61 0.49 — Minerals Calcium % 0.90 0.90 — Nonphytate phosphorus % 0.45 0.45 — Protein and amino acids Protein g — — 12 Argininec mg — — 680 Lysinec mg — — 475 Methioninec mg — — 340 Methionine + cystinec mg — — 490 Minerals         Calcium mg — — 200 Nonphytate phosphorus mg — — 110 NOTE: For nutrients not listed, see requirements for egg-type pullets (Table 2-3) as a guide. Where experimental data are lacking, values typeset in bold italics represent an estimate based on values obtained for other ages or related species. a Energy needs are influenced by the environment and the housing system. These factors must be adjusted as required to maintain the body weight recommended by the breeder. b Broilers do not have a requirement for crude protein per se. There, however, should be sufficient crude protein to ensure an adequate nitrogen supply for synthesis of nonessential amino acids. Suggested requirements for crude protein are typical of those derived with corn-soybean meal diets, and levels can be reduced somewhat when synthetic amino acids are used. c Amino acid requirements estimated by using the model of Smith (1978). reproductive performance (Wilson et al., 1971). Broiler breeder males can be fed 12 to 14 percent crude protein on a restricted basis after 4 weeks of age with no adverse effects on final body weight, sexual maturity, or semen quality; a greater number of males produced semen through 53 weeks when fed 12 percent crude protein than when fed higher levels (Wilson et al., 1987a). In a subsequent study (Wilson et al., 1987b), a 9 percent crude protein diet fed beginning at 43 days and continuing through 50 weeks was adequate to support maximum reproductive performance. In both these studies, amino acid content was maintained at a constant percentage of the protein level. There were no differences in semen characteristics of broiler breeder males fed 12 to 18 percent crude protein during the period from 4 to 20 weeks; males fed 15 percent crude protein during the period from 1 to 4 weeks had significantly higher fertility from 24 to 27 weeks than did males fed 20 percent crude protein (Vaughters et al., 1987). Semen production of broiler breeder males kept in cages can be maintained from 20 to 60 weeks on a daily protein intake of 10.9 to 14.8 g per day (Buckner and Savage, 1986). ENERGY Daily energy intakes of 400 (McCartney and Brown, 1980) and 458 kcal ME per bird (Brown and McCartney, 1983) have been reported as adequate for broiler breeder males maintained on litter. For broiler breeder males maintained in cages, 346 (Brown and McCartney, 1986) or 358 kcal ME per bird daily (Buckner et al., 1986) were sufficient. MINERALS The calcium requirement of the breeder cockerel is much lower than that of the hen, but levels fed to the hen apparently are not detrimental to the reproductive performance of the male. Wilson et al. (1969) indicated that the calcium requirement of SCWL cockerels did not exceed 0.2 percent, but that levels as high as 3 percent were not detrimental. In calcium balance studies with SCWL cockerels, Norris et al. (1972) found that the daily requirement was 7.98 mg per kg of body weight. Kappleman et al. (1982) concluded that there were no differences in the reproductive performance of broiler breeder cockerels fed 0.5 to 7 g of calcium daily per bird. Phosphorus Norris et al. (1972) found that diets containing 0.1 percent nonphytate phosphorus were satisfactory for SCWL cockerels. Bootwalla and Harms (1989) found that no more than 110 mg of nonphytate phosphorus per bird daily were needed for maintaining reproductive capacity and bone integrity in broiler breeder cockerels.