In this study the net requirements of energy and protein for weight gain were estimated through the comparative slaughter technique using 56 Nellore steers averaging 432 kg of initial body weight. The analytical composition of the 9th-10th-11th ribs was used to estimate empty body (EB) composition. Eight steers were slaughtered at the beginning of the trial to determine the initial body composition while the remaining steers were fed for 70 days diets containing 60% of concentrate (dry matter basis) composed by dry or high moisture corn grain with or without addition of ruminal protected fat. The average shrunk body weight at slaughter was 528 kg. Only hot carcass weight gain increased significantly by feeding ruminal protected fat to steers. No significant differences were observed for empty body composition, deposition rates and empty body gain composition among diets. Energy and protein requirements were 2.97 Mcal and 0.171 kg per kg of empty weight gain (EWG), respectively, while fat gain averaged 0.220 kg per kg of EWG. It can be suggested the use of high moisture corn and 4% of ruminal protected fat on diets for Nellore steers because no significant changes were found in body composition or net requirements of energy and protein.
beef cattle; body composition; feedlot; weight gain; animal nutrition
