Serum Levels of Insulin-Like Growth Factor-I, Thyroid Hormones and Skeletal Muscle Fiber Size in Castrated Lambs with and Without Androgen Treatment

Twelve, intact male lambs, 1-2- weeks old, were divided into 3 groups, Group W (4 lambs) were castrated at age less than 1 month, group WT (4 lambs) were castrated at the same age and treated with testosterone and group R (4 lambs) were left intact and served as control. Testosterone Propionate replacement was administered intramuscularly at a dose of 12.5 mg started at the day of castration and continued every 2 days for 21 days, then at a dose of 25 mg every 2 weeks until slaughter. Serum insulin-like growth factor-1, T3 and T4 concentrations were measured using ELISA. Lambs were slaughtered at 8 months of age and semitendinosus and splenius muscles fiber areas were measured using digital image technique. In WT and R groups, IGF-I concentrations were significantly higher (p<0.05) at 4 and 8 months compared to IGF-I levels in group W. Serum T3 concentrations were significantly lowest in group R compared to groups W and WT. Serum levels of T4 were not significantly affected by age in younger lambs, although it was significantly higher in group R at 6 and 8 months of age. In group R, splenius muscle fiber area (1458±193 um²) was significantly higher (p<0.05) than that of groups W and WT while the muscle fiber area of the semitendinosus muscle was not significantly different among all groups.