Effect of terbutaline and metaproterenol (two beta-adrenergic agonists) on performance and carcass composition of culled Moghani ewes

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. Terbutaline and metaproterenol, 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 Mcal/kg DM) of seven groups of 63 culled ewes and the other group was fed on LE (ME: 2.5 Mcal/kg DM) for the final 8 weeks of the fattening period. M10 and M20 equally increased (p < 0.05) total weight gain of ewes. The lowest (p < 0.05) amount of dry matter intake was observed in LE treatment. All metaproterenol-treated groups showed improved (p < 0.05) of feed efficiency compared with controls. Both the beta-agonists increased (p < 0.05) carcass efficiency compared with control. Total carcass crude protein was higher (p < 0.05) for ewes receiving the M20. Addition of terbutaline and metaproterenol to the diet had no significant effect on carcass fat and cavity fat weights; nevertheless, ewes treated with T20, M5, M10, M20 and LE had lower (p < 0.05) fat-tail weight than controls (3.44, 3.55, 3.54, 3.52 and 2.99 kg versus 4.52 kg). Blood urea concentration was reduced (p < 0.05) by LE treatment 12.6 and 23.8% on days 60 and 90, respectively. Results indicated that metaproterenol causes a repartitioning of nutrients resulting in improved feed efficiency, 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.