Body composition of lambs receiving 30 or 60 days of exercise training and (or) fenoterol treatment.
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The interaction between exercise and the beta-adrenergic agonist, fenoterol, on body composition and muscle protein turnover was studied in this investigation. Forty young Hampshire x Rambouillet lambs were assigned to control (CON), exercised (EX), fenoterol-treated (5 ppm) (FEN), or fenoterol-treated and exercised (FENEX) groups. Lambs assigned to the exercise treatments were trained to run on a 10 degrees inclined treadmill. The lambs were slaughtered after 30 or 60 days of treatment. Average daily gain tended (p = 0.09) to be greater, and feed:gain was significantly lower (p = 0.03) in the EX group than in the FENEX group by 30 days of treatment. By 60 days of treatment, kidney and pelvic fat and bodywall thickness were least in the EX group. Leg weights increased significantly with time only in the FEN and FENEX groups, whereas shoulder weights increased with time in all but the EX group. The latter effect was due to a cessation of adipose tissue growth in the EX lambs. There were significant time x treatment effects for the M. biceps femoris, M. gluteus medius, M. quadriceps femoris, M. semimembranosus, M. semitendinosus, M. infraspinatus, and M. pectoralis profundus. In every case, the time x treatment interaction was caused by nonsignificant growth of muscles in the CON group between 30 and 60 days. For the M. biceps femoris, M. quadriceps femoris, and M. gluteus medius, muscle mass increased with time only in the FENEX lambs. There was no increase in leg subcutaneous or intermuscular adipose tissue mass between 30 and 60 days in the EX lambs, although 50-70% increases in adipose tissue mass were observed over time in the other groups. Calpain and calpastatin activities in M. biceps femoris were not affected by treadmill exercise, fenoterol administration, or time x treatment (p > 0.72 for all effects). Myosin light chain-1 gene expression in the FENEX lambs was depressed by 60 d, suggesting that the rate of M. biceps femoris growth in this treatment group was slowing by this.