Authors : K.E. Moulton , T.G. Althen , A.B. Moore , M.B. Solomon , J.S. Eastridge and T.R. Smith
Abstract: The objective of this study was to determine effects of somatotropin (ST) and nutrition on growth, myofiber profiles, serum ST and IGF-1 values in beef calves. At 100 day of age, 48 crossbred steers were weaned and trained on the Calan Feeding System. At 155 day of age, steers were assigned to treatments in a 2�2 factorial design testing the effects of protein fed at levels according to NRC (NP) vs a high protein diet (125% of NRC, HP) and ST (Posilac, 2.2 mg�kg 1�14 day 1 s.c., ST) vs no ST (C). Blood samples were taken every 14 day for IGF-1 and ST analysis. Treatments continued until 255 day of age, when semitendinosus muscle biopsy samples were collected to determine myofiber morphology. The C-NP, C-HP and ST-NP steers consumed 7.7 kg�hd 1�d 1, which was 19% more than that consumed by ST-HP steers (6.52 kg�hd 1�d 1). The ST-treated steers had improved feed efficiency when compared to controls (0.17 vs 0.15 gain/feed). As expected, steers administered ST had increased serum ST concentrations over time and IGF-1 concentrations increased by 11% after week 4 compared to controls, however, cross-sectional areas for myofiber types and percentage distribution of slow- twitch-oxidative fibers were not different between treatments. The ST treatment resulted in a decreased percentage of fast-twitch-oxidative-glycolytic (26 vs 31%) and increased percentage of fast-twitch-glycolytic (58 vs 52%) fibers when compared to C steers. This data substantiates earlier findings and demonstrates that ST treatment alters myofiber morphology in beef calves, regardless of normal or high protein diets.
K.E. Moulton , T.G. Althen , A.B. Moore , M.B. Solomon , J.S. Eastridge and T.R. Smith , 2008. Effects of Recombinant Bovine Somatotropin (ST) and Protein on Growth and Muscle Fiber Profiles in Early-Weaned Beef Steers. Journal of Animal and Veterinary Advances, 7: 897-902.