Effects of feeding zilpaterol hydrochloride on feedlot performance and carcass characteristics of Nellore bulls and steers
This study, conducted at the São Paulo State University feedlot, Botucatu Campus, Brazil, was designed to determine the effects of feeding zilpaterol hydrochloride (ZH) on feedlot performance and carcass traits of Nellore steers and yearling bulls. The experiment was designed as a completely randomized block with a 2x2 factorial arrangement of treatments. Thirty-six 22-mo-old Nellore steers and 36 22-mo-old Nellore yearling bulls (483.9 ± 26.0 kg) were allocated in 24 pens and fed one of two finishing diets containing either 0.0 mg or 7.50 mg of ZH per kilogram of diet DM, replicated 6 times (3 animals/pen), for 20-d before slaughter with a 3-d withdrawal. The finishing diet contained: 70.0% high moisture corn grain, 15.0% sugarcane bagasse, 5.5% peanut meal, 4.0% cottonseed hulls, 3.0% supplement, 1.0% Coast cross hay, 0.8% urea, and 0.7% limestone (DM basis). Cattle were fed ad libitum twice daily for 112-d, and feed offerings and refusals were weighed daily. Cattle were weighed 20-d before slaughter and at the end of the study. A significant (P < 0.01) ZH main effect was observed, in which cattle fed ZH had greater final BW (518.6 vs. 510.3 kg) and ADG (1.73 vs. 1.31 kg), improved F:G ratio (5.55 vs. 7.55), heavier HCW (292.7 vs. 280.0 kg), and increased dressing percentage (56.6 vs. 55.1%). In addition, a significant ZH x sex interaction was observed (P = 0.04) for DMI, expressed in kg, in which steers not fed ZH had greater DMI than steers fed ZH (9.88 vs. 9.00 kg). However, yearling bulls not fed ZH presented similar DMI when compared to yearling bulls fed ZH (9.61 vs. 9.47 kg). Likewise, a significant ZH x sex interaction was observed (P = 0.03) for DMI, expressed as % of BW, in which steers not fed ZH had greater DMI than steers fed ZH (2.00 vs. 1.81%). However, yearling bulls not fed ZH presented similar DMI when compared to yearling bulls fed ZH (1.91 vs. 1.87%). Thus, feeding ZH improves the feedlot performance, as well as carcass traits of Nellore cattle regardless of sex.
Keywords: intake, sex, Zebu