Effect of recombinant bovine somatotropin on milk yield and composition in lactating goats

Eight multiparous lactating goats, matched for age and time of parturition, were used in a crossover experimental design in order to evaluate the effects of recombinant bovine somatotropin (rbST) on milk yield and composition. Treated goats were injected with 160 mg rbST at 14 day intervals for three consecutive 28 day periods. Supplementation with rbST significantly increased milk yield over the entire experimental period (1337+/-518 vs 1506+/-512, mean +/- S.D, p<0.01). Milk fat content was also increased during the treatment with rbST (2.9+/-0.55 vs 3.26+/-0.67, p<0.05). Protein concentration in milk was not significantly different between treated and control groups, while lactose levels exhibited a significant difference (p<0.01). Non-esterifred fatty acids tended to be higher in treated animals, but the results were not significantly different. Feed intake did not increase after hormone treatment.