Summary
For several decades, the National Research Council’s series on the nutrient requirements of beef cattle has provided vital information to nutritionists and academicians that has been essential for improving the economic and environmental sustainability of the beef industry. Each new edition in the series has proved its worth despite extensive changes in production and feeding practices, as well as biological types and physiological potential of cattle over time. The committee responsible for producing the eighth revised edition of the Nutrient Requirements of Beef Cattle has invested significant mental and physical capital into the revision process in an effort to ensure that the current edition continues to meet the high standards set by previous publications in the series.
The Statement of Task for the committee is in Appendix B. The basic charge was to update the seventh revised edition of the Nutrient Requirements of Beef Cattle, which was published in 1996 and the Update 2000 by reviewing the scientific literature on the nutrition of beef cattle for all life phases and types of production. Specific nutrients identified were amino acids, lipids, minerals, vitamins, and water, and an update on energy systems used in beef cattle nutrition was considered an essential component. A summary of the composition of feed ingredients, mineral supplements, and feed additives routinely fed to beef cattle, as well as information regarding byproduct feeds, particularly those from the biofuels industry, were additional areas identified as needing new or revised information. New data on nutrient metabolism (ruminal and postruminal) and consideration of feeding strategies to minimize nutrient losses in manure and decrease greenhouse gas production were to be included. Discussion of the nutritional quality and food safety of beef and future areas of needed research also were noted as essential components of the report, as was updating the computer model to calculate nutrient requirements.
As a result of the committee’s work, the text of the current edition has been expanded significantly, adding new topics and increasing discussion of components in the previous edition. New sections on beef cattle production systems, food quality, and safety; ruminant anatomy and digestion; carbohydrates; lipids; compounds that modify digestion and metabolism; nutrition and the environment; and byproduct feed ingredients are significant additions to previous reports in the series. Moreover, chapters that had been included in the previous edition were updated and expanded, with substantial effort to provide improved prediction equations for modeling various aspects of nutrient supply and metabolism and to evaluate new and existing equations. Specific changes in various chapters are described briefly in the following paragraphs.
Information on beef cattle production systems in North America is included in Chapter 1. This new section provides an important backdrop for understanding the settings from which data are derived to establish nutrient requirements and the typical conditions in which recommendations are applied. Additional new information on beef safety in terms of foodborne pathogens and antimicrobial resistance has been included, as well as a brief review of the nutritional profile of beef products. This chapter also points out the significance of animal welfare issues to the beef industry.
Chapter 2 is a comprehensive review of ruminant anatomy, digestion, and nutrient utilization. This new chapter provides the reader with a conceptual basis for establishing nutrient requirements of beef cattle and is particularly important for understanding the application of mechanistic models to beef cattle production.
Chapter 3 provides an update on energy terminology and concepts and includes updated information where available. The review of current data suggests that research efforts need to be focused on estimating the ratio of metabolizable energy to digestible energy across a range of dietary energy values.
Chapter 4 is a new chapter that provides a wide-ranging overview of the various types of carbohydrates used in ruminant production. As carbohydrates are the major source of energy in beef cattle diets, understanding their physiochemical properties and metabolism by ruminants is essential to understanding nutrient supply and development of models to predict requirements and performance of beef cattle. The role
of processing carbohydrate sources to alter nutrient supply and the importance of forage fiber in maintaining healthy rumen function also are reviewed in this chapter.
Information on the role of lipids in beef cattle nutrition is included in Chapter 5, which is also new to this edition. Processes of lipid digestion and absorption are described, and practical information on the energy value of lipid sources and supplementation of lipids in beef cattle diets is reviewed. Moreover, the importance of biohydrogenation of fatty acids by the ruminal microbial population is also considered, with the opportunity for implementation of fatty acid metabolism in future editions of the computer model.
The metabolizable protein (MP) system was adopted in the previous edition in the series as the basis for establishing the protein requirements of beef cattle. The MP system is reviewed and updated in Chapter 6. Important changes include new equations for predicting microbial protein synthesis, as well as an equation for predicting urea nitrogen used for anabolism (i.e., recycled nitrogen that is incorporated into microbial protein or other microbial products), which is a new and significant addition to the publication.
Chapter 7 provides an update of macro- and micromineral requirements for beef cattle. Factors that affect mineral requirements are discussed, as well as mineral-specific diseases that can influence beef cattle production. A significant amount of new information has been added relative to the role of sulfur in beef cattle production, which is particularly relevant with increased use of high-sulfur byproduct feeds.
Chapter 8 provides an update of beef cattle vitamin nutrition, with new information regarding the fat- and water-soluble vitamins. The review articulates issues associated with specific deficiencies and excesses and suggests areas for additional research. Of special note is the greater clarity that has been provided with respect to recommendations for provision of vitamin E in various production settings.
Of the six essential nutrient classes, water is the single most important nutrient for beef cattle. Chapter 9 provides an update of equations to predict water intake by beef cattle and examines factors that influence water intake, including the role of water quality in beef cattle production.
Accurate prediction of feed intake is essential to defining nutrient requirements and predicting performance. Factors affecting feed intake are reviewed in Chapter 10, and a larger database than used in the previous edition was assembled to reevaluate existing equations based on dietary net energy for maintenance concentrations and develop new ones for growing-finishing beef cattle. Equations for beef cows remain the same; however, additional guidance has been provided for predicting intake by beef cows, particularly those grazing forages.
Considerations related to energy and protein requirements for maintenance are discussed in Chapter 11. Factors affecting maintenance requirements are included in the discussion, equations to estimate requirements are provided, and gaps in our understanding are indicated. Greater discussion and cautionary statements about applying adjustments for cold stress and physical activity are important additions to this chapter.
Energy and protein requirements for growing and finishing cattle are reviewed in Chapter 12. No changes were made to the equations used in the previous edition; however, new data were used to provide additional evaluation of equations in predicting retained energy and protein.
The role of nutrition in reproduction of beef cows is vital to beef production, as reproductive efficiency is a major factor limiting productivity of beef herds. Chapter 13 provides a comprehensive review of the use of body condition scoring (BCS) as the basis for assessing the protein and energy requirements of beef cows. A significant change to the BCS-based system was the adoption of a fixed percentage of shrunk body weight (SBW) change per unit of BCS. New information on the role of nutrition in developmental programming also was added.
Information on compounds that modify digestion and metabolism of ruminants is the focus of Chapter 14. The chapter consolidates this information into one location and includes a more complete review of this topic than the previous edition. Updated guidelines for adjustments to dietary energy values associated with the use of ionophores are provided, as well as recommendations for adjustments to final SBW estimates associated with the use of implants and β-agonists in beef production.
Nutrient requirements as affected by stress, particularly those associated with weaning, marketing, transportation, new environments, and disease, are reviewed in Chapter 15. Adjustments to nutrient requirements associated with these stressors are suggested, with particular emphasis on accounting for effects of decreased feed intake in stressed beef cattle.
Chapter 16 is an important new addition to the publication that highlights the potential effects of livestock operations on the environment. Comprehensive reviews of factors affecting nutrient losses in feces and urine and emissions of greenhouse gases, ammonia, and other volatile compounds are provided. Significant effort was devoted to developing and evaluating prediction equations to estimate enteric methane production from low- and high-forage diets.
The increasing use of byproduct feeds in beef cattle production, especially those derived from production of grain-based biofuels, necessitated a thorough review of the utilization of these important feed ingredients in Chapter 17. Application in cow-calf, stocker, and growing-finishing settings is considered, and potential interactions with other ingredients and management practices, as well as the role of excess concentrations of some nutrients (e.g., sulfur) are considered.
An extensive, statistically based evaluation of a large amount of data from commercial laboratories was undertaken to provide the new feed composition tables that are included in Chapter 18. Information on the effects of grain processing on nutrient availability has been updated, and new data on composition of grazed forages were added.
The new computer model (Beef Cattle Nutrient Requirements Model) is described in detail in Chapter 19. In addition, sensitivity analyses are included to illustrate components of the model that have the greatest effect on predictions. The model software, which is spreadsheet-based, is substantially more intuitive and user-friendly than the software used in the previous edition. Users have a greater ability to turn specific calculations “on or off” and to change some coefficients to meet their needs. The software includes an optimizer to assist with diet formulation and balancing, an ability to perform stochastic modeling, and a table generator that allows the user to create tables of nutrient requirements through an optimization procedure that is described in Chapter 20. Finally, areas that need additional research to clarify mechanisms related to developing estimates of nutrient requirements and to more fully refine recommendations are highlighted in Chapter 21.
