Recombinant bovine somatotropin (rBST) administration in Simbrasil calves and its effects on muscle fibers and T3, T4 and IGF-I hormonal pattern

Abstract

In order to characterize the muscle fibers and alterations of the thyroid hormones and IGF-I, 64 Simbrasil male and female calves, from 60 until 210 days-old, were supplemented in creep-feeding, with recombinant bovine somatotropin (rBST). A dose of 0.15 mg of rBST/kg of body weight was administrated every 14 days in the animals with rBST. The muscle fibers were characterized, and the proteins were quantified. Alterations hormones and IGF-I were also evaluated. It was not observed any increase in the average diameter of the three types of muscle fibers. The myofibril protein content of the muscle from the rBST female calves increased, and the same were observed in male calves, independent of rBST administration. It was not found any influence of rBST administration in the T3 hormone, although the female calves (2.37ng/mL) had greater T3 concentration than the male calves (1.95ng/mL). Regarding the T4 hormone, female calves had greater concentration than male calves, in which the rBST administration resulted in a decrease of T4 concentration. The female calves had lower IGF-I concentration than the male calves, but rBST administration caused an increase in the IGF-I concentration in both gender. In conclusion, the rBST administration did not promote an increase in the muscle fiber diameter, and it happened with the myofibril protein content of the muscle from the females calves. Also, rBST did not influence T3 concentration, reduced T4 in male calves and increased IGF-I concentration in both gender.