Ambient temperature and other environmental factors usually were not specified in papers presenting requirements data. Most experiments, however, have been conducted under moderate conditions, with temperatures of 16° to 21°C and relative humidities of 40 to 60 percent. When temperature or humidity conditions deviate from these ranges, adjustments in nutrient concentrations may be needed to compensate for changes in feed intake.

Chapter 2, on the nutrient requirements of chickens, has been divided according to Leghorn-type and meat-type fowl. For the former, sections are included for starting and growing pullets and for hens in egg production. Similarly, for the latter, separate sections are presented for starting and growing market broilers, broiler breeder pullets and hens, and broiler breeder males. Requirements of starting and growing turkeys and turkey breeders are given in Chapter 3. Nutrient requirements of geese, ducks, and pheasants and quail are provided in Chapters 4, 5, and 6, respectively. These data, however, were based on a relatively meager amount of literature.

Chapter 7, on signs of nutritional deficiencies in chickens and turkeys, has been enlarged considerably to include more descriptive information and documentation. Tables present biochemical and physiological indicators of nutrient deficiencies, signs of nutrient deficiencies in embryos, and nutrient deficiencies that may be associated with specific deficiency signs. Chapter 8 includes an update presentation on toxic levels of elements as related to diets or drinking water.

Feedstuff composition data and related information are presented in Chapter 9. The tabular data of Tables 9-2 and 9-3 have been revised according to recent analytical results obtained with contemporary feedstuffs. This revision primarily involved changes in proximate and amino acid compositions of numerous feedstuffs. True metabolizable energy (TMEn) values of many feedstuffs also have been included in Table 9-2. Two new sections have been added to Chapter 9. One section briefly discusses and presents equations estimating amino acid composition on the basis of protein content or proximate analysis. The second covers amino acid availability and includes a listing of true digestibility coefficients for selected amino acids in many poultry feedstuffs. The tabular presentation in Chapter 9 on fatty acid composition and MEn values of dietary fats for poultry is extensive and well documented. Information on the crude protein equivalents and nitrogen-corrected MEn values of amino acids and on the element concentrations in common mineral sources also is provided.

The nutrient composition of feedstuffs is, of course, variable. In addition, the effective concentrations of nutrients in diets may be reduced by inadequate feed mixing, improper processing, and unfavorable storage conditions. Nutritionists may accordingly add a "margin of safety" to the stated requirements in arriving at nutrient allowances to be used in formulation to compensate for these aforementioned conditions.

Examples of practical, semipurified, and chemically defined reference diets for chicks are given in Chapter 10.

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