Productive performance, composition and carcass yield of lambs treated with zeranol

Twenty weaned male hair lambs with average body live weight of 19.20 kg±2.18 kg (SD) were used to evaluate the effect of zeranol on growth, composition and carcass yield. The animals were distributed into a completely randomized design with two treatments: no anabolics (control); and treatment with zeranol, using a subcutaneous dose of 10 mg/50 kg body live weight. Lambs received a diet with 15 g/100 g of crude protein and 2.8 Mcal of metabolizable energy/kg dry matter for 84 days. At the end of experiment all animals were harvested and entire carcass and its parts (neck, shoulder, loin-rib, loin-skirt and leg) were weighed to determine the composition of muscle and bone. Control animals had higher dry matter intake (1.01 vs 0.88 kg/d), average daily gain (198 vs 172 g/animal) and total weight gain (12.9 vs 10.9 kg) compared with those treated with zeranol. Zeranol group had higher muscle weight (1.76 vs 1.98 kg) and less bone (0.86 vs 0.61 kg) in leg section. The leg area represented about 16 kg/100 kg of the carcass weight for both treatments. No differences for other carcass traits were observed. Lambs treated with zeranol have better leg conformation because they develop more muscle mass, though their average feed intake and daily gain decrease.