The ninth revised edition of Nutrient Requirements of Poultry contains substantially more information than previous editions. In addition to presenting updated nutrient requirements data, this edition includes more discussion on key facets of nutrients, nutrient requirements, and nutrient sources. Detailed documentation of the scientific literature used to establish or estimate the requirements is also included in Appendix A.
Scientifically based knowledge about many nutrient requirements is incomplete. Consequently, calculations and interpolations were necessary to derive estimated requirements. These nutrient requirements were derived mostly from empirical observations of responses of poultry to changes in dietary concentrations or intakes of specific nutrients. In some instances, nutritional models were used to estimate amino acid requirements.
Few nutritional models are available for poultry, primarily because data to support the development of these models are scarce. There are, however, modeling equations for estimating the energy and amino acid requirements of poultry. Hurwitz et al. (1978) integrated the energy and amino acid needs of broiler chicks to develop a mathematical model for predicting amino acid requirements. Models for estimating the amino acid requirements of growing turkeys were proposed by Fisher (1982a) and Hurwitz et al. (1983a). Modeling equations also have been developed for predicting the energy requirements (National Research Council, 1987a) and amino acid requirements (Hurwitz and Bornstein, 1973) of laying hens. Additional research is needed to determine maintenance requirements and partial efficiency of nutrient use for growth versus egg production.
Energy, specific nutrients, and certain nonnutritive feed ingredients are discussed in general terms in Chapter 1. Definitions of terms used to describe the energy value of poultry feeds are given, and an expanded section on procedures for determining and estimating dietary metabolizable energy is provided. General aspects of protein and amino acid nutrition and metabolism have been updated. The section on fats includes information on sources, factors affecting metabolizable energy (MEn) values, effects on composition of poultry products, and metabolic functions. Overviews are given for minerals, vitamins, and water. Data on water consumption for chickens and turkeys have been revised according to recent field observations of contemporary breeds and strains. General characteristics and uses of xanthophylls, unidentified growth factors, and antimicrobials in poultry diets also are discussed.
Nutrient requirements for specific types of poultry are presented and discussed in Chapters 2 through 6, with each chapter devoted to a different type. Each of these chapters contains a table or tables detailing the nutrient requirements of the respective groups. Requirements data are presented on the basis of 90 percent dietary dry matter, which approximates most feeding conditions. These data are also presented on the basis of total concentrations in the diet or total consumed per day, not on an available or digestible basis.
In the tables, requirements that are well delineated in the literature, the ''established requirement," are set in regular type. "Estimated requirements," made on the basis of meager data or by interpolation, are set in bold italicized type. In some instances, the committee decided to insert a question mark rather than make estimates with no bases.
The committee emphasizes that the requirements values reported herein have not been increased by a "margin of safety." The values represent the judgment of the subcommittee after its review of the published data. Criteria of adequacy included growth, reproduction, feed efficiency, health, and quality of poultry products.
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.