Dietary energy level and β2-adrenergic agonist supplementation on growth performance, dietary energy, carcass traits, and visceral mass of hairy lambs

Context The beta-agonist zilpaterol (ZH) is a feed additive that improves growth performance via protein accretion during the finishing phase of ruminant fattening. However, evaluating the possible interaction between ZH and nutrients of the diet has received limited attention. Aims We investigated the changes in growth performance and carcass traits in response to ZH supplementation of hairy lambs fed finishing diets with different energy concentration. Methods Forty-eight Pelibuey × Katahdin crossbred male lambs (43.8 ± 6.3 kg) were used in a 34-day feeding trial to evaluate the interaction between diet energy density [8.37 (LE) and 8.79 (HE) MJ of net energy for maintenance (NEm) per kilogram of diet] and zilpaterol hydrochloride supplementation (ZH, dosed at 0 or 6 mg ZH/kg) on growth performance, carcass traits, and visceral mass. All diets contained 14.5% crude protein (CP). Key results There was no interaction of energy level and ZH in any of the variables evaluated. HE increased average daily gain (ADG) and gain efficiency (GF) without affecting the observed-to-expected dietary NE. Zilpaterol supplementation increased ADG, GF, and observed-to-expected dietary NE. Both HE and ZH increased carcass weight. HE increased carcass fat, whereas ZH decreased it. HE increased dressing percentage. ZH increased longissimus muscle area, the muscle:fat ratio in the shoulder, and leg whole-cut proportion. Visceral mass was not affected by energy level. ZH decreased visceral fat. Conclusions Increasing diet energy from 8.37 to 8.79 MJ NEm/kg enhanced growth performance and carcass traits but did not improve dietary energy utilization. Supplemental ZH enhanced growth performance, dietary-energy utilization and carcass traits of lambs. Implications ZH supplementation is a tool to enhance growth performance by improving protein accretion and reducing carcass fat. Response to ZH supplementation is independent of the differences in energy density of finishing diets.