Effects of recombinant bovine somatotropin administration to lactating goats

Eight multiparus lactating goats, matched for parity and days in milk were used to evaluate the effects of recombinant bovine somatotropin (rbST) administration on milk yield and composition, as well as on certain metabolic parameters. The experiment was a switch-back design, with three periods lasting 28 days each. Animals were divided into two groups (n ˆ 4) and treatments consisted of subcutaneous injection of 160 mg rbST at 14-day intervals. Controls remained uninjected. Supplementation with rbST increased milk yield signi®cantly over the entire experimental period (1506 80.8 vs. 1337 81.8 ml/day, p < 0.05). Percentage of fat in milk was greater for goats treated with rbST than controls, (3.26 0.09% vs. 2.9 0.08%, p < 0.05), while protein percentage did not differ (p > 0.05) between treated and control animals. Lactose content also increased after rbST administration (3.88 0.06% vs. 3.55 0.06%, p < 0.01). Plasma NEFA and bhydroxybutyrate levels were not affected by treatment. Short-chain fatty acids in milk were similar in both groups. In conclusion, rbST administration increased milk yield and the percentage of fat and lactose in milk, while no effect was recorded in milk protein content. # 2000 Elsevier Science B.V. All rights reserved.