294. Energetics and Energetic Efficiency of Beef Cows.

Abstract The US beef cattle industry is based on production of calves under extensive pasture and range conditions. Even after calves are weaned, pasture and forage remain the main ingredients in growing diets. It is only after calves enter the feedlot phase that grain and grain co-products comprise finishing diets. Although microbes in ruminant digestive tracts have the capacity to digest high-fiber diets, the energetic efficiency of the US beef industry is inherently low. Studies conducted in the 1980’s and 1990’s led to our current understanding of energy requirements for maintenance of beef cows. Subsequent studies described energetic efficiency at weaning or finishing. Studying effects of breed on energy requirements likely motivated those efforts. Indirect calorimetry determinations based on whole body dissection or body composition by indirect methods (dilution techniques or body condition score and weight), and gas exchange measurements were common methods used then. Recent determinations of energy requirements and energetic efficiency are based on gas exchange measurements and body composition determined indirectly from body condition score and weight. The objective of this review aided by meta-analytical methods is to understand whether energy requirements for maintenance of beef cows have changed over time. Concurrently, using the most probable estimate of energy requirements for maintenance, this review attempts to determine the energetic efficiency of the cow-calf production segment and its 20-year trend based on observations drawn from regional USDA market reports.