The objectives of this study were to compare the efficacy of 3-week vs 6-week dietary administration of the
beta-adrenergic agonist cimaterol on skeletal muscle growth, and to measure the changes in muscle
nucleic acid and
protein concentration and content to provide evidence regarding the mechanism(s) by which
cimaterol stimulates muscle
hypertrophy in growing ruminants. Two groups of 12 Dorset or Dorset-Finn cross ram lambs weighing 36 kg or 33 kg were assigned to treatment intervals of 3 or 6 weeks, respectively. Lambs within each weight group were randomly assigned to receive 0 or 10 ppm
cimaterol in a complete mixed diet fed ad libitum. Initial live weights and treatment periods were chosen to achieve similar slaughter weights.
Cimaterol increased the mass of three hind leg muscles 30% and 25% on average (both P less than .001) with 3- and 6-week administration, respectively, resulting in identical average muscle weights of treated lambs at both treatment intervals. The mean mass of these 3 muscles, expressed as a percentage of
body weight, was increased 18.6% (P less than .001) at both treatment intervals.
RNA concentration and content of the semitendinosus muscle were increased 24.8% (P less than .01) and 84.6% (P less than .001), respectively, after 3 weeks of treatment, but neither was significantly different from controls after 6 weeks.
DNA concentration in the muscle was reduced 42% (P less than .05) with 3-week
cimaterol administration, and was 25% less than controls (P greater than .05) in lambs fed
cimaterol for 6 weeks. Total
DNA content of the semitendinosus was unchanged at either treatment interval.(ABSTRACT TRUNCATED AT 250 WORDS)