Daily optimal level of a generic beta-agonist based on zilpaterol hydrochloride for feedlot hair lambs

Two experiments were completed to determine the dietary optimal dose of a generic product (Grofactor®) of zilpaterol hydrochloride (ZH) in fattening male lambs. In experiment 1, 32 lambs were assigned to four daily doses of ZH (n = 8): 0 (Control), 0.10, 0.20, and 0.30 mg/kg of body weight (BW). In experiment 2, the doses of ZH with the best biological response from experiment 1 (i.e., 0.10 and 0.20 mg/kg of BW per lamb) were compared using 18 lambs (9 lambs per treatment), as well as a control group of 9 lambs. In experiment 1, growth rate, feed efficiency, hot (HCW) and cold (CCW) carcass weight and dressing percentage showed a quadratic increase (P ≤ 0.05) as the dose of ZH increased, but all these traits were similar among ZH-fed lambs. Yield of wholesale cuts was not impacted by ZH dose. Percentages of skin and foot decreased linearly (P ≤ 0.01) with increasing ZH dose. However, head, liver, and stomach had a quadratic effect (P ≤ 0.05) to increasing levels of ZH, with the lowest values at the intermediate ZH addition levels. In experiment 2, ZH-fed lambs compared with control had better (P ≤ 0.04) feedlot performance, HCW, CCW, dressing percentage, Longissimus dorsi muscle area and carcass length. Addition of ZH only increased (P ≤ 0.03) the leg yield using any of the doses. Feeding ZH decreased (P ≤ 0.03) the percentages of blood, liver, spleen, and stomach, while percentage of lungs increased (P < 0.01). In both experiments, ZH supplementation had no effect on fat thickness, and omental and mesenteric fat. We concluded that generic ZH is effective as growth promoter in male lambs finished in feedlot to a daily dosage of 0.10 mg/kg of BW.