The objective of this study was to evaluate the effects of recombinant bovine somatotropin (rbST) on production, carcass traits, and plasmatic concentrations of IGF-I and thyroid hormones on crossbred Angus-Nellore male calves. Thirty-six calves averaging 63 ± 17 days old and 76.8 ± 14.7 kg of body weight (BW) grazing Brachiaria decumbens and creep fed were randomly assigned (18 calves per treatment) to one of two treatments until weaning (217 days) as follows: I) 1.4 mg of rbST (Boostin®)/kg of BW every 14 days or II) similar dosage of saline solution. Every 28 days calves were weighed and blood samples collected; at weaning, five animals from each treatment were slaughtered for carcass evaluation. The rbST-treated calves had greater average daily weight gain, final weight, and plasmatic concentrations of both IGF-I and T4 than those receiving saline solution. Weights of hot carcass, forequarter, hindquarter, hindquarter muscles, and liver as well as dressing percentage, kidney and pelvic fat, rib eye area, backfat thickness, and plasmatic concentrations of T3 were all not affected by rbST. Use of rbST increased body weight gain (7.9%) and changed the hormonal status of pre-weaning creep-fed calves compared to the use of saline solution but did not improve carcass weight or dressing percentage.
creep feeding; growth; calves
