Effect of Two Beta-Adrenergic Agonists on Performance and Carcass Composition of an Iranian Native Breed of Sheep

The effects of terbutaline (T), metaproterenol (M) and low energy diet (LE) on growth performance and carcass composition were evaluated in 72 Moghani culled ewes. T and M each one at the doses of 0, 5, 10 and 20 mg/ kg DM (C, T5, T10, T20, M5, M10 and M20 respectively) were added to the diet (ME: 2.9 MJ/Kg DM) of seven groups of 63 culled ewes and the other group was fed on LE (ME: 2.5 MJ/Kg DM) for the final 8 wk of the fattening period. T10 and M20 increased (p<0.05) final and cold carcass weights of ewes. LE ewes had lower daily dry matter intake than controls (1126 vs. 1500 g/day). Except for T5 and LE, all beta- adrenergic treated groups showed improved (p<0.05) of food conversion efficiency of 17.6% to 26.9 % compared with controls. Increased (p<0.05) carcass efficiency was obtained by M5, M10 and M20 relative to controls (49.94%, 50.07% and 50.64% vs. 46.31%). Total carcass protein was higher (p<0.05) for ewes receiving the M20. Ewes treated with T20, M5, M10, M20 and LE had lower (p<0.05) fat-tail weight than controls (3.64, 3.55, 3.54, 3.52 and 3.99 kg vs. 4.52 kg). Blood urea concentration was reduced by L E treatment 12.5% and 23.8% on days 60 and 90 respectively. Results indicated that metaproterenol causes a repartitioning of nutrients resulting in improved feed conversion, increased carcass meat and lowered weight of-fat tail. Metaproterenol was more effective on feedlot parameters and carcass characteristics than terbutaline and low energy diet.