3
Nutrient Requirements of Turkeys

The nutrient requirements of turkeys are divided into needs of birds used as a source of growth and needs of those for reproduction. These two categories differ largely in the proportion of nutrients devoted to productive use as opposed to those used for maintenance activities.

Requirement values given in Table 3-1 are usually minimum levels that satisfy general productive activities and(or) prevent deficiency symptoms. The values given often represent an approximation of values from more than one study. Where information is lacking, italicized values represent an estimate based on values obtained for other ages or related species. Values selected by the committee as best representing the requirement were those for which the research was recent and performed under practical terms in which all nutrient needs in addition to the nutrient in question were satisfied. The experimental data from the peer-reviewed scientific literature that are the basis for the committee's nutrient requirement recommendations are given in Appendix Table A-4.

STARTING AND GROWING TURKEYS

The growth rate of turkeys has increased greatly during the past decade. Approximate live body weights per age and feed consumption data of contemporary turkeys are shown in Table 3-2. Increased growth rates have occurred through the efforts of the major commercial breeders, and parent stock has increased in size as well, particularly the hen. Further processing of the carcass into convenience products also has expanded and now occupies the greatest part of total production.

Substantial improvements in the rates of gain and feed efficiencies of commercially available strains have occurred during the last decade. The nutrient requirements given in Table 3-1 are based on earlier research and the chronological age of the experimental turkeys used at that time. For the most part, these nutrient levels are still being employed by the industry at large; however, because of improvements in growth rates these levels are now being used at earlier ages. Such changes have not been experimentally verified as being appropriate, but commercial results indicate satisfactory performance. Examples of these age adjustments for male and female turkeys are shown in Table 3-1, footnotes a and b, respectively.

Commercially available strains of turkey may differ in the chronology of their development. The nutrient requirements given on Table 3-1 represent the approximate needs for development of large-type turkeys. Medium- and small-type turkeys finish progressively earlier than the large. For the given nutrient levels to be employed effectively, those levels representing each age interval should be provided according to the corresponding stages of development.

The requirements are expressed as concentrations in the feed. These concentrations are such that adequate total intake is ensured and the nutrient balance is favorable. Both factors are necessary. A balanced feed having lower nutrient concentrations than shown may not permit sufficient intake to meet the bird's absolute need. Conversely, an increased concentration of nutrients ensures adequacy but may not be cost effective.

Pelleting is widely practiced in feed manufacturing, and feeding a pelleted diet usually leads to an improvement in performance. Pelleting may increase nutrient digestibility in some constituent feedstuffs; however, the primary result is improved use of the nutrients already available apparently because of reduced physical activity by the bird. Generally, pelleting facilitates feed intake, increases net energy of production from metabolizable energy (ME), and reduces overall feed wastage (Moran, 1989b). These benefits are accentuated as feed nutrient level decreases and as birds become progressively older, provided the feed remains in pelleted form.



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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 3 Nutrient Requirements of Turkeys The nutrient requirements of turkeys are divided into needs of birds used as a source of growth and needs of those for reproduction. These two categories differ largely in the proportion of nutrients devoted to productive use as opposed to those used for maintenance activities. Requirement values given in Table 3-1 are usually minimum levels that satisfy general productive activities and(or) prevent deficiency symptoms. The values given often represent an approximation of values from more than one study. Where information is lacking, italicized values represent an estimate based on values obtained for other ages or related species. Values selected by the committee as best representing the requirement were those for which the research was recent and performed under practical terms in which all nutrient needs in addition to the nutrient in question were satisfied. The experimental data from the peer-reviewed scientific literature that are the basis for the committee's nutrient requirement recommendations are given in Appendix Table A-4. STARTING AND GROWING TURKEYS The growth rate of turkeys has increased greatly during the past decade. Approximate live body weights per age and feed consumption data of contemporary turkeys are shown in Table 3-2. Increased growth rates have occurred through the efforts of the major commercial breeders, and parent stock has increased in size as well, particularly the hen. Further processing of the carcass into convenience products also has expanded and now occupies the greatest part of total production. Substantial improvements in the rates of gain and feed efficiencies of commercially available strains have occurred during the last decade. The nutrient requirements given in Table 3-1 are based on earlier research and the chronological age of the experimental turkeys used at that time. For the most part, these nutrient levels are still being employed by the industry at large; however, because of improvements in growth rates these levels are now being used at earlier ages. Such changes have not been experimentally verified as being appropriate, but commercial results indicate satisfactory performance. Examples of these age adjustments for male and female turkeys are shown in Table 3-1, footnotes a and b, respectively. Commercially available strains of turkey may differ in the chronology of their development. The nutrient requirements given on Table 3-1 represent the approximate needs for development of large-type turkeys. Medium- and small-type turkeys finish progressively earlier than the large. For the given nutrient levels to be employed effectively, those levels representing each age interval should be provided according to the corresponding stages of development. The requirements are expressed as concentrations in the feed. These concentrations are such that adequate total intake is ensured and the nutrient balance is favorable. Both factors are necessary. A balanced feed having lower nutrient concentrations than shown may not permit sufficient intake to meet the bird's absolute need. Conversely, an increased concentration of nutrients ensures adequacy but may not be cost effective. Pelleting is widely practiced in feed manufacturing, and feeding a pelleted diet usually leads to an improvement in performance. Pelleting may increase nutrient digestibility in some constituent feedstuffs; however, the primary result is improved use of the nutrients already available apparently because of reduced physical activity by the bird. Generally, pelleting facilitates feed intake, increases net energy of production from metabolizable energy (ME), and reduces overall feed wastage (Moran, 1989b). These benefits are accentuated as feed nutrient level decreases and as birds become progressively older, provided the feed remains in pelleted form.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 TABLE 3-1 Nutrient Requirements of Turkeys as Percentages or Units per Kilogram of Diet (90 percent dry matter)     Growing Turkeys, Males and Females Nutrient Unit 0 to 4 Weeksa; 0 to 4 Weeksb; 2,800c 4 to 8 Weeksa; 4 to 8 Weeksb; 2,900c 8 to 12 Weeksa; 8 to 11 Weeksb; 3,000c 12 to 16 Weeksa; 11 to 14 Weeksb; 3,100c 16 to 20 Weeksa; 14 to 17 Weeksb; 3,200c 20 to 24 Weeksa; 17 to 20 Weeksb 3,300c Breeders   Holding; 2,900c Laying Hens 2,900c Protein and amino acids Proteind % 28.0 26 22 19 16.5 14 12 14 Arginine % 1.6 1.4 1.1 0.9 0.75 0.6 0.5 0.6 Glycine + serine % 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.5 Histidine % 0.58 0.5 0.4 0.3 0.25 0.2 0.2 0.3 Isoleucine % 1.1 1.0 0.8 0.6 0.5 0.45 0.4 0.5 Leucine % 1.9 1.75 1.5 1.25 1.0 0.8 0.5 0.5 Lysine % 1.6 1.5 1.3 1.0 0.8 0.65 0.5 0.6 Methionine % 0.55 0.45 0.4 0.35 0.25 0.25 0.2 0.2 Methionine + cystine % 1.05 0.95 0.8 0.65 0.55 0.45 0.4 0.4 Phenylalanine % 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.55 Phenylalanine + tyrosine % 1.8 1.6 1.2 1.0 0.9 0.9 0.8 1.0 Threonine % 1.0 0.95 0.8 0.75 0.6 0.5 0.4 0.45 Tryptophan % 0.26 0.24 0.2 0.18 0.15 0.13 0.1 0.13 Valine % 1.2 1.1 0.9 0.8 0.7 0.6 0.5 0.58 Fat Linoleic acid % 1.0 1.0 0.8 0.8 0.8 0.8 0.8 1.1 Macrominerals Calciume % 1.2 1.0 0.85 0.75 0.65 0.55 0.5 2.25 Nonphytate phosphorusf % 0.6 0.5 0.42 0.38 0.32 0.28 0.25 0.35 Potassium % 0.7 0.6 0.5 0.5 0.4 0.4 0.4 0.6 Sodium % 0.17 0.15 0.12 0.12 0.12 0.12 0.12 0.12 Chlorine % 0.15 0.14 0.14 0.12 0.12 0.12 0.12 0.12 Magnesium mg 500 500 500 500 500 500 500 500 Trace minerals Manganese mg 60 60 60 60 60 60 60 60 Zinc mg 70 65 50 40 40 40 40 65 Iron mg 80 60 60 60 50 50 50 60 Copper mg 8 8 6 6 6 6 6 8 Iodine mg 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Selenium mg 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Fat soluble vitamins A IU 5,000 5,000 5,000 5,000 5,000 5,000 5,000 5,000 D3g ICU 1,100 1,100 1,100 1,100 1,100 1,100 1,100 1,100 E IU 12 12 10 10 10 10 10 25 K mg 1.75 1.5 1.0 0.75 0.75 0.50 0.5 1.0 Water soluble vitamins B12 mg 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 Biotinh mg 0.25 0.2 0.125 0.125 0.100 0.100 0.100 0.20 Choline mg 1,600 1,400 1,100 1,100 950 800 800 1,000 Folacin mg 1.0 1.0 0.8 0.8 0.7 0.7 0.7 1.0 Niacin mg 60.0 60.0 50.0 50.0 40.0 40.0 40.0 40.0 Pantothenic acid mg 10.0 9.0 9.0 9.0 9.0 9.0 9.0 16.0 Pyridoxine mg 4.5 4.5 3.5 3.5 3.0 3.0 3.0 4.0 Riboflavin mg 4.0 3.6 3.0 3.0 2.5 2.5 2.5 4.0 Thiamin mg 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 NOTE: Where experimental data are lacking, values typeset in bold italics represent estimates based on values obtained from other ages or relate species or from modeling experiments. a The age intervals for nutrient requirements of males are based on actual chronology from previous research. Genetic improvements in body weight gain have led to an earlier implementation of these levels, at 0 to 3, 3 to 6, 6 to 9, 9 to 12, 12 to 15, and 15 to 18 weeks, respectively, by the industry at large. b The age intervals for nutrient requirements of females are based on actual chronology from previous research. Genetic improvements in body weight gain have led to an earlier implementation of these levels, at 0 to 3, 3 to 6, 6 to 9, 9 to 12, 12 to 14, and 14 to 16 weeks, respectively, by the industry at large. c These are approximate metabolizable energy (ME) values provided with typical corn-soybean-meal-based feeds, expressed in kcal MEn/kg diet. Such energy, when accompanied by the nutrient levels suggested, is expected to provide near-maximum growth, particularly with pelleted feed. d Turkeys 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. e The calcium requirement may be increased when diets contain high levels of phytate phosphorus (Nelson, 1984). f Organic phosphorus is generally considered to be associated with phytin and of limited availability. g These concentrations of vitamin D are considered satisfactory when the associated calcium and phosphorus levels are used. h Requirement may increase with wheat-based diets.

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 TABLE 3-2 Growth Rate and Feed and Energy Consumption of Large-Type Turkeys Age (weeks) Body Weight (kg) Feed Consumption per Week (kg) Cumulative Feed Consumption (kg) ME Consumption per Week (Mcal)   Male Female Male Female Male Female Male Female 1 0.12 0.12 0.10 0.10 0.10 0.10 0.28 0.28 2 0.25 0.24 0.19 0.18 0.29 0.28 0.53 0.5 3 0.50 0.46 0.37 0.34 0.66 0.62 1.0 1.0 4 1.0 0.9 0.70 0.59 1.36 1.21 2.0 1.7 5 1.6 1.4 0.85 0.64 2.21 1.85 2.5 1.9 6 2.2 1.8 1.10 0.80 3.31 2.65 3.2 2.3 7 3.1 2.3 1.40 0.98 4.71 3.63 4.1 2.8 8 4.0 3.0 1.73 1.21 6.44 4.84 5.0 3.5 9 5.0 3.7 2.00 1.42 8.44 6.26 6.0 4.3 10 6.0 4.4 2.34 1.70 10.78 7.96 7.0 5.1 11 7.1 5.2 2.67 1.98 13.45 9.94 8.0 5.9 12 8.2 6.0 2.99 2.18 16.44 12.12 9.0 6.8 13 9.3 6.8 3.20 2.44 19.64 14.56 9.9 7.6 14 10.5 7.5 3.47 2.69 23.11 17.25 10.8 8.4 15 11.5 8.3 3.73 2.81 26.84 20.06 11.6 9.0 16 12.6 8.9 3.97 3.00 30.81 23.06 12.3 9.6 17 13.5 9.6 4.08 3.14 34.89 26.20 13.1 10.1 18 14.4 10.2 4.30 3.18 39.19 29.38 13.8 10.5 19 15.2 10.9 4.52 3.31 43.71 32.69 14.5 10.9 20 16.1 11.5 4.74 3.40 48.45 36.09 15.2 11.2 21 17.0 a 4.81 a 53.26 a 15.9 a 22 17.9 a 5.00 a 58.26 a 16.5 a 23 18.6 a 5.15 a 63.41 a 17.1 a 24 19.4 a 5.28 a 68.69 a 17.4 a a No data given because females are usually not marketed after 20 weeks of age. Energy In calculating the total metabolizable energy for the complete feed, the metabolizable energies provided by each feedstuff are assumed to be additive. The MEn content of the complete feed influences feed intake, which, in turn, may influence the concentrations of most other nutrients that are needed to satisfy requirements. An inverse relationship exists between the MEn concentration of the diet and feed consumption of turkeys. However, as discussed in Chapter 1 (Setting Dietary Levels), changes in dietary MEn concentration and thus, the use of specific nutrient-to-dietary MEn ratios in formulating turkey diets is questionable, especially when economical growth and feed efficiency are primary objectives (Pesti and Fletcher, 1983; Sell et al., 1985; 1989). The MEn levels given in Table 3-2 at each age period are not intended to be absolute but to establish a feed intake reference for other nutrients. The energy and amino acid levels given would be satisfied largely when corn and soybean meal are combined with a small amount of added fat, in turn permitting near-maximum growth. Nutrient levels may be increased without adversely affecting performance; however, a moderate reduction in nutrient levels would likely require pelleting of the associated feed to prevent adverse effects on growth rate. Net energy of production is difficult to estimate because maintenance expenditures vary extensively. Environmental temperature is one of the most influential factors affecting maintenance, which, in turn, may lead to changes in feed intake. Changes in the maintenance energy requirement in response to environmental temperature may not be linear. Hurwitz et al. (1980) observed that the maintenance energy requirement for both sexes of turkeys, during the period from 32 to 60 days of age, was between 2.45 and 2.70 kcal/g67 of body weight at 12°C. This requirement progressively decreased from 12° to 24°C, then remained constant between 24° and 28°C and increased thereafter through 35°C. The maintenance energy need in response to temperature also differs with age. In a study on the 20-week-old male turkey, Hurwitz et al. (1983b) found the requirement at 10°C to approximate 2.15 kcal/g67, but unlike the requirement for the younger bird (32 to 60 days) there was an uninterrupted decrease through to 35°C. In both of these studies the advantage to net energy of production increased as temperature increased; however, feed intake and growth were not altered accordingly. Protein And Amino Acids A protein requirement of 28 percent for starting poults is supported by the work of Lloyd et al. (1949), Atkinson et al. (1957), Herz et al. (1975a), and Richter et al. (1980). Reduced levels of protein can decrease early growth, but if the protein reduction is moderate, compensatory gain of large-type turkeys prior to marketing may overcome the deficit. The progressive reduction in the protein requirement as the turkey grows is well established. A level of 12 percent protein with 2,900 kcal ME/kg for holding turkeys prior to reproduction is consistent in terms of the protein:energy ratio with the 14 percent protein at 3,526 kcal MEn reported by Meyer et al. (1980a). The protein need for egg production has been observed to vary from 10 to 18 percent of the diet, with the value of 14 percent chosen as being the most representative. Research on the amino acid requirements of turkeys has largely been conducted on the starting poult. With the exception of lysine and the sulfur amino acids, little experimentation has been done to determine the amino acid requirements of growing turkeys. Fisher (1982a) and Hurwitz et al. (1983a) employed body analyses and feed intake together with calculated maintenance needs to estimate requirements. The protein requirements shown in Table 3-1 are based on either actual experimentation, modeling, or are calculated as a ratio with lysine when the requirement for lysine at the ages in question has been measured experimentally. The starting poult's arginine requirement of 1.6 percent of the diet is supported by the research of Almquist (1952) and Warnick and Anderson (1973) and the modeling of Hurwitz et al. (1983a). Dunkelgod et al. (1970) and D'Mello and Emmans (1975) reported higher arginine requirement

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 values when they fed amino acid mixtures or diets based on wheat-corn gluten meal, respectively. The isoleucine requirement listed for starting turkeys (1 percent of the diet) is based largely on the research of Warnick and Anderson (1973) and agrees well with the value of 1.03 percent obtained from modeling by Hurwitz et al. (1983a). Similarly, the leucine requirement (1.9 percent of the diet) is based on the determined value of 1.86 percent reported by Warnick and Anderson (1973) and 1.96 percent from modeling by Hurwitz et al. (1983a). The lysine and sulfur amino acid needs have been well investigated because of their frequent limitation under practical conditions. Starting poults require 1.6 percent lysine in the diet. This value represents an average of the determined values 1.55 percent (Balloun and Phillips, 1957b), 1.6 percent (Kummero et al., 1971), 1.68 percent (Warnick and Anderson, 1973), 1.5 percent (Tuttle and Balloun, 1974), and 1.55 percent (D'Mello and Emmans, 1975). The value of 1.42 percent obtained by modeling (Hurwitz et al., 1973) is noticeably lower than those measured by bioassay. Lysine needs after the first 4 weeks of life have been derived mainly from the research of Tuttle and Balloun (1974), Jensen et al. (1976), and Potter et al. (1981). The poult's requirement of 0.55 percent methionine in the diet is greater than the 0.53 percent given in the previous edition of this report and is the value that best represents the reports of Almquist (1952), Baldini et al. (1957), and Murillo and Jensen (1976a). Requirement values beyond starting were provided from the experimentation of Murillo and Jensen (1976a) and Behrends and Waibel (1980). The total sulfur amino acid requirement value of 1.1 percent for starting poults was derived from the observations of 1.04 percent by Warnick and Anderson (1973), 1.05 percent by Murillo and Jensen (1976b), 1.10 percent by Potter and Shelton (1979), and 1.1 percent by Behrends and Waibel (1980), as well as the 1.05 percent from modeling by Hurwitz et al. (1983a). Requirement values specifically for methionine subsequent to starting largely represent the observed needs to optimize performance as reported by Potter and Shelton (1979, 1980), Murillo and Jensen (1976a), and Behrends and Waibel (1980), together with the modeling estimate by Hurwitz et al. (1983a). Minerals The calcium requirement determined with starting poults has been reported to be as high as 1.7 percent (Motzok and Slinger, 1948) and 1.5 percent (Wilcox et al., 1953) and as low as 1.0 percent (Slinger et al., 1961) and 0.81 percent (Formica et al., 1962). Neagle et al. (1968) reported a requirement of 1.2 percent dietary calcium when total phosphorus and vitamin D levels were 0.8 percent and 1,100 ICU/kg of diet, respectively. The latter calcium requirement for growing turkeys has been substantiated by Nelson et al. (1961), Sullivan (1961), and Formica et al. (1962). Hens in egg production need approximately 2.25 percent calcium in the feed, as shown by Balloun and Miller (1964a), Arends et al. (1967), Potter et al. (1974), and Waldroup et al. (1974b). The nonphytate phosphorus requirement of 0.6 percent for starting poults agrees with the research reported by Almquist (1954), Bailey et al. (1986), and Stevens et al. (1986). This value has been shown to decrease with age (Day and Dilworth, 1962; Sullivan, 1962). Reported nonphytate phosphorus requirements for breeder hens in egg production range from 0.3 percent (Waldroup et al., 1974b; Slaugh et al., 1989) to 0.55 percent (Atkinson et al., 1976). The latter relatively high value probably occurred because of a low phosphorus availability in the feedstuffs employed; thus 0.35 percent was selected to represent the requirement. The magnesium requirement, given as 500 mg/kg of diet, has been reduced from the 600 mg listed in the previous edition to better reflect the value of 475 mg/kg reported by Sullivan (1964). The manganese requirement may vary with the type of diet and supplement used. The recommended value of 60 mg/kg is the same as the requirement observed by Kealy and Sullivan (1966). The same level was reported by Atkinson et al. (1967b) as the requirement for breeder hens. Zinc needs are known to depend on the levels of other dietary constituents. The recommended level of 70 mg/kg was determined with practical diets having phytic acid present, whereas 41 mg/kg were adequate in a purified diet where phytic acid was absent (Dewar and Downie, 1984). Vitamins The previous requirement for vitamin A was listed as 4,000 IU/kg of diet. Vitamin A at 5,000 IU/kg of feed provides for maximum growth performance and liver storage (Prinz et al., 1986) and has been chosen to represent the requirement, although 2,000 IU/kg will also support optimal performance (Prinz et al., 1983). Vitamin A at 5,000 IU/kg is also recommended for breeder hens, but lower levels (about 2,500 IU/kg) have been shown to maintain egg production, hatchability, and survival (Stoewsand and Scott, 1961; Jensen et al., 1965). Vitamin D3 at 900 IU/kg of feed has been shown to be more than adequate for the starting poult in most studies (Baird and Greene, 1935; Hammond, 1941; Stadelman et al., 1950); however, Neagle et al. (1968) found that 1,100 IU/kg was necessary to maximize both growth and toe ash concentration when the diet contained 1.2 percent calcium and 0.8 percent total phosphorus. Discrepancies in vitamin D3 needs of poults

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Nutrient Requirements of Poultry: Ninth Revised Edition, 1994 may relate to the level of this vitamin in the breeder hen's feed. Stevens et al. (1984) observed that 900 IU/kg in the breeder hen's diet supported maximum egg yield, hatchability, and subsequent survival of the poult, but liver storage was considered marginal. The value given as the vitamin E requirement of starting turkeys is the same as that reported by Scott et al. (1965) when the dietary selenium concentration was 0.1 mg/kg. The vitamin E requirement of breeder hens was observed to be twice this level (24 IU/kg; Jensen and McGinnis, 1957). Extensive increases in vitamin E well above requirements for optimal growth are necessary in order to provide the carcass meaningful protection against oxidative rancidity when carcasses are held in frozen storage (Sheldon, 1984). All other vitamin requirements have been determined only for the first 4 or 8 weeks of age. In some instances, there is good agreement among the researchers on the requirement value but, in other instances, considerable disparity exists. The committee has revised the requirement values given for several vitamins either to better represent old information or to reflect new reports. Vitamin K at 1 mg/kg of diet was increased to 1.75 mg/kg to be the same as the value observed by Griminger (1957) to optimize blood prothrombin time. The new value is considered adequate under practical conditions because poults used by Griminger (1957) were reared in wire-floored pens and coprophagy, as an additional source of vitamin K, was prevented. Ruiz and Harms (1989a) reported that the poult's requirement for riboflavin was greater than 3.5 mg/kg of diet. The value given in the previous edition was 3.6 mg/kg, and this has been increased to 4.0 mg/kg. Conversely, Ruiz and Harms (1989b) reported the pantothenic acid requirement to be less than 8.6 mg/kg of diet; thus the previously listed requirement of 11 mg/kg was reduced to 10 mg/kg. The dietary need for choline is known to be influenced by the levels of other nutrients involved in methyl group metabolism. The previously listed choline requirement was 1,900 mg/kg of diet, which was largely based on the report of Evans (1943), wherein the levels of ancillary nutrients influential to methyl group metabolism were not ensured. Harms and Miles (1984) reported that the choline requirement for poults between 0 and 4 weeks of age was less than 1,490 mg/kg of diet. Blair et al. (1986), using turkeys between 4 and 8 weeks of age, reported that the requirement was less than 1,250 mg/kg. To reflect these observations, the present requirement has been reduced to 1,600 and 1,400 mg/kg of diet for the period from 0 to 4 and 4 to 8 weeks, respectively. The requirements for many vitamins after 8 weeks of age have not been determined for turkeys. Only measurements of the vitamin D3, pantothenic acid, biotin, and folacin requirements have been conducted on breeder hens. TABLE 3-3 Body Weights and Feed Consumption of Large-Type Turkeys during the Holding and Breeding Periods   Females Males Age (weeks) Weight (kg) Egg Production (%) Feed per Turkey Daily (g) Weight (kg) Feed per Turkey Daily (g) 20 8.4 0 260 14.3 500 25 9.8 0 320 16.4 570 30 11.1 0a 310 19.1 630 35 11.1 68 280 20.7 620 40 10.8 64 280 21.8 570 45 10.5 58 280 22.5 550 50 10.5 52 290 23.2 560 55 10.5 45 290 23.9 570 60 10.6 38 290 24.5 580 NOTE: These values are based on experimental data involving ''in-season" egg production (that is, November through July) of commercial stock. It is estimated that summer breeders would produce 70 to 90 percent as many eggs and consume 60 to 80 percent as much feed as in-season breeders. a Light stimulation is begun at this point. Requirement values for other vitamins were estimated from experimentally determined values for younger ages and changes in requirements observed with chickens. TURKEY BREEDERS Through the first 12 to 16 weeks of age, male and female turkeys being grown for reproductive purposes generally have been fed the same diet as birds intended for meat production. Thereafter, various efforts have been implemented to avoid obesity. Limiting body weight gain of males by either restricting feed access (Krueger et al., 1978) or providing a low-protein feed for ad libitum consumption (Meyer et al., 1980b) is effective as long as the practices are not so severe that they delay semen production. Typical nutrient levels employed from this time through the active breeder period correspond to those of the holding feed, as given in Table 3-1. Excess body weight of hens is less of a problem than with males because an extensive loss of body weight occurs with hens as time in lay progresses. Table 3-3 includes a sample of hen performance through the breeder period. Inadequate body weight gain prior to stimulatory lighting delays the onset of lay and reduces egg production (Krueger et al., 1978; Meyer et al., 1980a). Starting both sexes on feed having the lowest concentration of nutrients for which a balance can be formulated and continuing this regimen to and through the breeder period on an ad libitum consumption basis minimizes the likelihood of obesity without adversely affecting performance (Ferket and Moran, 1985, 1986).