Effect of the Zilpaterol Hydrochloride Supplementation Strategies in Feedlot Lambs: Growth Performance, Dietary Energetics, Carcass Traits, and Meat Quality

The objective of this study was to evaluate the effects of zilpaterol hydrochloride supplementation strategies on growth performance, dietary energetics, carcass traits, and meat quality in feedlot finishing lambs. Twenty-four Dorper × Katahdin crossbred male lambs (45.5 ± 4.53 kg, mean ± SD) were used in a 27 d feeding trial. The zilpaterol supplementation strategies were: (1) control, no zilpaterol supplementation (CON); (2) zilpaterol administered once daily as a full dose in the morning feeding (ZMOR); (3) zilpaterol incorporated into the total mixed ration and continuously available throughout the day (ZMIX); and (4) intermittent zilpaterol supplementation applied in a daily alternating pattern, one day on, one day off (ZINT). A target dose of 0.20 mg/kg live weight of zilpaterol hydrochloride per administration was used for all supplemented treatments, with daily administration in ZMOR and ZMIX and alternate-day administration in ZINT. Compared to the CON, zilpaterol supplementation through the ZMOR + ZMIX strategies improved average daily gain (ADG) and feed efficiency (FE) by 28.6% and 18.5%, respectively. Additionally, dressing percentage and longissimus thoracis muscle area increased by 3.2% and 17.0%, respectively. The ZINT strategy also enhanced ADG by 20.9% and FE by 15.4%. However, ZINT did not improve hot carcass weight or dressing percentage. All zilpaterol supplementation strategies increased meat toughness by up to 39.2%. Results indicate that both the ZMOR and ZMIX strategies optimize the response to zilpaterol, with no evidence that ZMOR supplementation results in a diminished response.