INFLUENCE OF THE BETA-ADRENERGIC AGONIST CIMATEROL ON BODY-COMPOSITION AND WHOLE-BODY SYNTHESIS AND DEGRADATION OF PROTEIN IN GROWING LAMBS

A study was undertaken to determine the effect of dietary cimaterol at low (1.1 x maintenance (M)) followed by high (2.2 x M) feed intake on body composition and protein metabolism in growing lambs fed alfalfa pellets. Control (n = 5), cimaterol I (n = 5) and cimaterol II (n = 4) lambs received rations containing cimaterol at 0, 10. 9 and 0 mg kg-1 of dietary dry matter (DM) at 1.1 x M and 0, 10.9 and 10.9 mg kg-1 DM at 2.2 x M intake, respectively. On day 22 at each feeding level, whole-body protein turnover was determined as estimated from 6-h continuous infusions of 1-[C-14]-leucine. Longissimus dorsi areas (P=0.03) and the weights of psoas major, gastrocnemius (P<0.01) and semitendinosus (P=0.06) muscles were increased in lambs fed cimaterol throughout the experiment. There was an increase in leucine irreversible loss (P=0.006), whole body protein synthesis (P=0.004) and accretion (P=0.001) at the high compared to low intake. At the low intake, protein accretion was increased (P<0. 1) from 63 g d-1 in control lambs to 94 g d-1 in cimaterol-treated lambs. No difference could be detected in whole-body protein accretion in the lambs at the high feeding level. It was concluded that cimaterol-fed lambs had higher accretion of protein in muscles than control lambs and that increases in protein accretion due to cimaterol could be detected by the radioleucine method at the low-intake level but not at the high-intake level. Large differences in estimates for protein accretion obtained from leucine metabolism, nitrogen balance and liveweight gain data suggest that refinements in techniques for estimating whole-body protein synthesis and degradation are needed.