Effects of zilpaterol hydrochloride and soybean oil supplementation on feedlot performance and carcass characteristics of hair-breed ram lambs under heat stress conditions.

Forty Dorper × Pelibuey ram lambs initially weighing 31.7 ± 2.30 kg were stratified by BW and randomly assigned to treatments under a completely randomized design with a 2 × 2 factorial arrangement of treatments to evaluate effects of zilpaterol hydrochloride (ZH; 0 or 10 mg/lamb daily) and soybean oil (SBO; 0 or 6%) on feedlot performance, carcass characteristics, and wholesale cut yield of ram lambs under heat stress conditions. After a 34-d feeding period, all lambs were harvested. Climatic conditions were of moderate heat stress (average temperature 35.7°C) for lambs during the study. Interactions ZH × SBO were not observed (P ≥ 0.11) for any of the variables evaluated. During the first 17 d of experiment, ZH increased (P ≤ 0.05) BW, ADG, and G:F without affecting feed intake (P = 0.40), but from d 18 to 34 and the entire 34-d feeding period, feedlot performance was not affected (P = 0.18) by ZH. Also, ZH decreased KPH, dressing percent, LM area, LM pH at 24 h postmortem, and leg perimeter (P ≤ 0.04). Renal fat (P = 0.03) decreased with ZH while other noncarcass components were not affected (P ≥ 0.06) by ZH supplementation. Leg yield (P = 0.01) and plain loin (P = 0.04) decreased with ZH and yields of other wholesale cuts were not affected (P ≥ 0.10) by ZH. Feedlot performance (P ≥ 0.20) and wholesale cut yield (P ≥ 0.21) were not affected by SBO. Additionally, dressing percentage decreased (P < 0.01) with SBO while other carcass characteristics (P ≥ 0.12) were not affected by SBO. In conclusion, inclusion of both ZH and SBO in feedlot finishing diets did not improve feedlot performance, carcass characteristics, or wholesale cut yield of hair-breed ram lambs under moderate heat stress. Feedlot performance responded only to ZH and only during the first 17 d of the feeding period. In addition, some carcass characteristics of economic importance, such as dressing, LM area, and leg yield, were improved by ZH.