Twenty-four Dorper × Pelibuey ewe lambs initially weighing 25.1 ± 0.6 kg were used in a 34-d feeding experiment and after slaughter to evaluate the effect of zilpaterol hydrochloride (ZH) on feedlot performance, carcass characteristics, and wholesale cut yield. Ewe lambs were individually housed in pens, blocked by initial BW, and assigned randomly within BW blocks to 1 of 2 treatments: 1) control (no ZH) and 2) supplemented with ZH (10 mg/ewe lamb daily) during 32-d and a 2-d withdrawal preslaughter period. Feeding ZH increased (P < 0.01) final BW, ADG, and G:F of ewe lambs, whereas feed intake was unaffected (P = 0.80). Hot and cold carcass weights, dressing percentage, and conformation score were improved (P < 0.001) when ZH was fed. Likewise, LM area was 3.7 ± 0.41 cm² larger (P < 0.001) for ZH than control ewe lambs. Feeding ZH did not affect (P ≥ 0.29) cooling loss, carcass length, fat thickness, or KPH. With exception of peritoneum (P < 0.001), head (P = 0.021), and neck (P < 0.001), ZH did not increase (P ≥ 0.12) noncarcass components or wholesale cut yield percentage. A trend to increase (P = 0.060) loin percentage from HCW was observed in lambs supplemented with ZH. In conclusion, feeding ZH to Dorper × Pelibuey ewe lambs improved feedlot performance and also some carcass traits (HCW, cool carcass weight, dressing percentage, and LM area) of economic importance; however, fat deposition was not affected by ZH. Copyright © 2011. American Society of Animal Science .

The objective of the present study was to evaluate the effects of supplementation of zilpaterol hydrochloride (ZH) to the finishing diets on the feedlot performance and carcass characteristics of hair sheep ewe lambs during hot environmental conditions. Twenty Katahdin × Pelilbuey and Dorper × Pelibuey crossbred females with an average initial liveweight (LW) of 26.2 ± 0.83 kg were blocked by the initial LW, and assigned individually to 20 pens in a closed calf-rearing unit provided with fans. Treatments were (1) control group (basal diet without ZH) and (2) ZH group (basal diet plus 10 mg of ZH/ewe.day). Skin temperatures were measured each 2 days in five ewes by treatment; ambient weather conditions were recorded every day. After a 34-day feeding period, all ewes were slaughtered. Climatic variables during the study showed severe heat stress, with the average temperature–humidity index and temperature 85 units and 34.1°C, respectively. The skin temperature of belly and right flank was greater (P < 0.05) in ZH females than in control lambs. Ewe lambs fed ZH had feedlot performance, carcass length, shear force, body fat and skin percentage similar (P > 0.05) to control ewe lambs. With the exception of peritoneum and head (P < 0.05), all visceral organs had similar (P > 0.05) percentages between treatments. However, hot- and cool-carcass weights, dressing percentage, conformation and rib-eye area were greater (P < 0.05) for ewes supplemented with ZH. Likewise, the weight of hindquarter, legs and ribs expressed as a percentage of hot-carcass weight increased (P < 0.05) with ZH supplementation. Growth and deposition of excessive fat in hair-sheep ewe lambs were not improved with ZH supplementation under heat-stress conditions, whereas carcass-quality traits such as dressing and rib-eye area were increased.