RESUMO
The objective of this study was to evaluate the effects of combining immunocastration and ß-adrenergic agonists (ß-AA) on blood metabolites and their correlations with performance and carcass traits of Nellore cattle. Ninety-six Nellore males were distributed in a randomized block design with a 2×3 factorial arrangement. The factors were two sexual conditions (immunocastrated and non-castrated), and three diets (control, with no inclusion of ß-AA; RH, with 300 mg of ractopamine hydrochloride/d; and ZH, with 80 mg of zilpaterol hydrochloride/animal/d). The trial was conducted during 100 d, during which animals were fed ZH and RH for the last 30 and 33 d, respectively. Blood metabolites related to lipid and protein metabolism were assessed at the baseline (0 d of ß-AA supplementation) and after 13 and 30 d of ß-AA supplementation. No effect of sexual condition × ß-AA supplementation × time on feed interaction was observed. Combining immunocastration with ß-AA supplementation modified cholesterol and non-esterified fatty acids concentrations without affecting protein metabolism. Immunocastration enhances lipogenesis and reduces skeletal muscle accretion by increasing high-density lipoprotein and triglycerides concentrations and decreasing creatinine and creatine kinase concentrations, respectively. Zilpaterol hydrochloride enhances skeletal muscle accretion by decreasing urea and total protein concentrations and increases creatinine and creatine kinase concentrations without modifying lipid metabolism.(AU)