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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
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.
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).