Feed Intake and Carcass Composition of Angus and Santa Gertrudis Steers Fed Diets of Varying Energy Concentration

Abstract

Twenty Angus and 20 Santa Gertrudis steers were fed five diets varying from 2.8 to 3.6 kcal/g of digestible energy (DE) to study the relationships between dry matter (DM) and DE intake and dietary DE concentration. Daily gain, feed intake per unit of metabolic size and feed efficiency were similar between breeds when results with all five diets were averaged. DM intake was explained approximately equally well whether regression functions were linear or hyperbolic with respect to dietary DE concentration. The linear and hyperbolic functions for the combined breed data were: DM intake (g/W-75) = 227.9-38.4 X DE (kcal/g) and DM intake (g/W-75) = -19.2 + 394.3/DE (kcal/g) with Sy.x of 12.5 and 12.3, respectively. Linear and hyperbolic functions of DM intake multiplied by dietary DE concentration become quadratic and linear functions of DE intake, respectively.The Angus were slaughtered at 450 kg, the Santa Gertrudis at 550 kg, and the effects of incremental changes in dietary DE concentration on carcass desirability and tissue fatty acids were determined. Carcass marbling and grade tended to be highest for cattle fed the diet with the greatest DE concentration, and Angus graded higher and had more marbling (P<.01) than Santa Gertrudis. The percentages of palmitic and stearic acids in ether extractable lipid tended to decrease with increasing concentrations of DE in the diet whereas the percentages of oleic and linoleic acids tended to increase. Adipose tissue of Santa Gertrudis was more saturated than that of Angus.