Overview of the process and changes in the 8th Edition of the Nutrient Requirements of Beef Cattle

Abstract Text: The National Research Council’s (NRC) series on Nutrient Requirements of Beef Cattle has been an essential information resource for practicing nutritionists and academicians for decades. Standards set by NRC publications have improved economic and environmental sustainability of the beef industry, and each revision has provided a stimulus for further research. The committee responsible for the 8^th edition invested more than 2 yr in producing a revision that would meet the high standards set by previous publications in the series. Following the Statement of Task, the committee updated the 7^th revised edition by reviewing the scientific literature on the nutrition of beef cattle for all life phases and various production settings. Several new sections were added, including: 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. Chapters from the 7^th edition were updated, with substantial effort to provide improved prediction equations for modeling nutrient supply and metabolism. Specifically, new equations for predicting microbial protein synthesis and recycled nitrogen that is incorporated into microbial products were added. New information was included relative to the role of sulfur in beef cattle production, particularly as it relates to high-sulfur byproduct feeds. Greater clarity is provided on recommendations for provision of vitamin E in various production settings, and new equations were provided for prediction of feed intake by growing/finishing beef cattle. The body condition score-based system was changed to include a fixed percentage of shrunk BW change per unit of BCS, and updated guidelines for adjustments to dietary ME values associated with the use of ionophores are provided. A new chapter is devoted to the potential effects of livestock operations on the environment, and prediction equations for nutrient excretion and enteric methane production are included. Byproduct feeds are described in much greater detail, and a statistically based evaluation of a feed composition data from commercial laboratories is provided. The new computer model, with options for empirical and mechanistic solutions, is more intuitive and user-friendly than software provided with the 7th edition. The 8^th edition of the Nutrient Requirements of Beef Cattle is a major revision that should have a significant effect on beef cattle research and production over the next decade.

Keywords: beef cattle, nutrient requirements, revision