Abstract #T332

# T332
Evaluation of the feedlot performance, carcass yield, and production costs of finishing beef cattle supplemented with β-agonists.
Silvia Larios-Cueto1, Gilberto Aranda-Osorio*1, Rodolfo Ramirez-Valverde1, Hermilo Suarez-Dominguez1, Jose M. Monzon-Armenta1, 1Universidad Autonoma Chapingo, Chapingo, Texcoco, Mexico.

The objective of the this study was to evaluate the effect of β-agonists (zilpaterol and ractopamine hydrochloride) supplementation on finishing beef cattle performance and carcass quality. These agonists are approved in Mexico. There were used 50 7 commercial crossbred (Bos taurus × Bos indicus) young bulls, initially weighing 446.3 ± 9.0 kg, from the tropical region (Veracruz State), and allotted to 3 pens (19 each) of the Experimental Feedlot Facilty of the University of Chapingo (Mexico State a temperate region), each pen was randomly assigned to the following treatments: 1) Control (no supplement added), 2) Ractopamine (0.91 mg/kg of body weight (BW) per day) and 3) Zilpaterol (0.15 mg/k of BW per day). All animals received the same finishing diet, which has the following calculated nutritional composition: 14.48% CP; 1.79 and 1.16 Mcal/kg of NEm and NEg, respectively, 11.16% CF, and 2.2 Ca:P. At the moment that cattle arrived to the feedlot they received a prophylactic management (identified, weighed, vaccinated, dewormed, vitamined and implanted). The β-agonists were supplemented at least 35 d at the end of the finishing period. The variables evaluated were: dry matter intake (DMI), average daily gain (ADG), feed:gain (F:G), gain:feed (G:F), hot carcass yield (HCY), trimmed carcass fat (TCF) and benefit/cost (B/C) ratio. Data were analyzed under a completely randomized design with the GLM procedure of SAS, and to compare means the Tukey Test was performed. The only variable that was not statistically analyzed was DMI because it was calculated collectively. Cattle performed very similarly and no differences (P > 0.05) were found among treatments, the mean values being 11.88 kg/animal perday for DMI, 1.80 kg for ADG, 7.35 kg for F:G, 143 g/kg for G:F, 57.7% for HCY and 2.2% for TCF. Although, the B/C ratio was better for ractopamine treatment (1.13 vs. 1.05 for control and zilpaterol, respectively). Under the conditions of this study, the supplementation of β-agonists (ractopamine or zilpaterol hydrochloride) during the finishing period of young bulls showed a tendency to increase animal performance and carcass traits, but only ractopamine demonstrated to be profitable.

Key Words: bullock, ractopamine, zilpaterol