Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Overview This seventh revised edition of Nutrient Requirements of requirements in this edition, it is necessary to know both Beef Cattle is a significant revision of the sixth edition. the crude protein concentration in the feedstuffs being used One major improvement involves expansion in describing as well as the rumen degradability of that protein. different cattle. Requirements are also defined in terms of Modeling the dynamic state of nutrient requirements a greater variety of management and environmental in cattle is a major departure for those familiar with seeing conditions than was possible in previous editions. One nutrient requirements in tabular form only. To satisfy those result of this innovation is that there is now a greater who might wish to use the information in a format similar responsibility for the user to define the animals and their to the previous edition, a table generator is provided. conditions before proceeding to determine nutrient However, because of the dynamic state of protein digestion, requirements. protein requirements in the table generator are expressed A second major improvement involves presentation of as metabolizable rather than crude protein. requirements using computer models. Computer models The model prepared in this publication is at two levels. are the only effective way to take animal variation into For the first level, equations are very similar to equations account. Also important is the fact that computer models used in the sixth edition. Revision of requirements at this can describe the dynamic state of the animal, which is level have, for the most part, only updated equations when not possible with the presentation of discrete tabular values there was sufficient new information to justify this. The of nutrient requirements alone. The dynamic state of subcommittee chose to add a second modeling level, which describing nutrient requirements of ruminants refers here is more mechanistic than level 1 and was included to to the fact that feed ingredients can affect absorbable describe the dynamic state of digestion in and passage of nutrients, hence potential performance, which has a digesta through the reticulo-rumen. Level 1 is feedback on requirements. This situation is best illustrated recommended for users who were comfortable with using with protein. Diet can have a major effect on protein, nutrient requirements recommended in the previous edition which is degraded in the rumen or undegraded and of this publication and who want the greatest accuracy in bypassed to the lower portion of the gastrointestinal tract. evaluating requirements. Level 2 is offered as a model to Energy in the diet affects the amount of microbial protein give a greater interpretation of the results, for example to that can be synthesized in the rumen. Hence, the amount diagnose underperformance of animals on a given diet. of total true protein that the animal absorbs from the gut, The subcommittee anticipates that as users become equivalent to metabolizable protein, depends on the energy comfortable with level 2 in accuracy of prediction, level and degradable protein level of the diet. Net energy and 2 will become the modeling level used to evaluate rations metabolizable protein set the potential growth, as well. reproductive, or lactational performance, which then Chapter 1 contains a discussion of energy as a nutrient dictates the need for other nutrients, such as calcium and by providing basic definitions and terms used to describe phosphorus. For these reasons, the subcommittee chose to energy content of feedstuffs. There is also an extensive present nutrient requirements in terms of evaluating rations discussion of maintenance energy and factors such as cattle or diets, rather than as discrete recommendations for breed, sex, physiological state, and environment that can nutrients to fulfill a given level of performance. Net energy alter maintenance requirements. This chapter concludes is used to evaluate ration and diet energy, which is the with a discussion of use of energy from body weight loss. same format used in the sixth edition. To evaluate protein 1
2 Nutrient Requirements of Beef Cattle Chapter 2 is a review of protein digestion and included in this chapter and differentiates recommendations metabolism and presents the basis for considering according to physiological function. Sufficient information metabolizable protein (MP), or amino acids absorbed from exists to specify higher levels of magnesium, potassium, the gastrointestinal tract, and the utilization of MP in sodium (salt), and manganese in diets for breeding cattle, setting protein requirements for beef cattle. There is a particularly lactating animals, compared to growing and discussion of factors affecting microbial protein synthesis, finishing cattle. Calcium and phosphorus requirements, which includes consideration of needs for energy and as in the previous edition, are presented in equation format degradable protein. A value for the maintenance (in Chapter 7) to calculate recommended daily intakes requirement for protein, based on metabolic and for a comprehensive description of cattle types and endogenous losses of nitrogen, is proposed as well as an management circumstances. Calcium requirements are equation to estimate conversion of MP to net protein. similar to those established in the previous edition of this Chapter 2 concludes with a section on validation of publication, but phosphorus requirements have been recommendations for protein requirements of both modified slightly from the previous edition and are growing-finishing and breeding cattle. discussed in the context of some recent studies on these A discussion of cattle size and body composition with minerals. reference to energy and protein begins Chapter 3. This Maximum tolerable concentrations of other minerals discussion provides the basis for using mature size as a have been listed in Chapter 5. In the case of chromium, reference point to unify description of nutrient requirements molybdenum, and nickel, evidence that these minerals across animals of different mature size and as affected by are essential to cattle has been presented, but there are liveweight, age, and physiological state. To use a system insufficient data on which to base dietary requirements. of nutrient requirements based on a constant body fat Requirements for vitamins and water have been composition, it is necessary to understand factors that affect considered in Chapter 6. Besides the fat-soluble vitamins, rate of growth such as use of anabolic implants or for which the evidence to support a required concentration ionophores, and a discussion of these is included. Chapter in the diet is very strong, the literature on the water-soluble 3 also includes a discussion of compensatory growth and B vitamins is reviewed to document where supplementation validation of the energy and protein requirement system. of diets for beef cattle may be beneficial. A discussion of In addition, Chapter 3 considers predicting target weight water requirements of beef cattle includes a table detailing gains for replacement heifers and discusses variables that these requirements as affected by ambient temperature affect nutrient requirements of breeding females. Chapter and physiological function and liveweight. 3 concludes by describing a mechanism to predict energy Factors affecting feed intake of beef cattle are reviewed reserves of beef cows through the use of body condition in Chapter 7. This chapter includes a review of how score, body weight, and body composition. It provides a physiological factors affect feed intake. There is a section relationship between condition score and percent fat in on prediction of feed intake by beef cattle and this includes the body. validation of equations used for the models of requirements. Unique considerations in setting nutrient requirements There is a special section in this chapter to consider intake for breeding animals are considered in Chapter 4. It of all-forage diets. includes a discussion of factors affecting calf birth weight, Chapter 8 provides an overview of the effects of stress energy, and protein requirements for gestation, and on nutrient requirements. Effects on energy, protein, nutrient metabolism by the gravid uterus and placenta. In mineral, and vitamin requirements are addressed. the discussion of lactation requirements, Chapter 4 reviews Chapter 9 presents the application of new information the literature on determining milk yield in beef cows and to formulate equations and models for nutrient energy requirements for milk production. This chapter requirements. Tables of requirements generated by the also describes factors affecting heifer development and model are provided for growing-finishing steers or heifers, breeding performance of mature cows and bulls. for pregnant replacement heifers, for lactating cows, and Macromineral and micromineral requirements are for bulls. A step-by-step example of how to predict average presented in Chapter 5. Where possible, discussion of each daily gain and crude protein requirements is also presented. mineral includes the role of the mineral in physiological Chapter 10 provides all of the equations used in the processes of cattle, the bases for setting requirements of model plus a thorough description of the data contained these nutrients, and relevant aspects about digestion, in the feed library on the model disk. absorption, and metabolism. Signs of deficiency, factors Chapter 11 provides tables of nutrient composition of affecting requirements, and toxicity and maximum feedstuffs commonly used in beef cattle diets, including tolerable concentrations in diets are discussed also. A table estimates of variation of nutrient content and discussion summarizing recommended dietary concentrations and of processing effects. maximal tolerable concentrations of some minerals is