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) admi nistration on milk yield and composition, as well as on certain metabolic p arameters. The experiment was a switch-back design, with three periods last ing 28 days each. Animals were divided into two groups (n = 4) and treatmen ts consisted of subcutaneous injection of 160 mg rbST at 14-day intervals. Controls remained uninjected. Supplementation with rbST increased milk yiel d significantly 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 goat s 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 an d control animals. Lactose content also increased after rbST administration (3.88 +/- 0.06% vs. 3.55 +/- 0.06%, p < 0.01). Plasma NEFA and beta-hydrox ybutyrate levels were not affected by treatment. Short-chain fatty acids in milk were similar in both groups. In conclusion, rbST administration incre ased milk yield and the percentage of fat and lactose in milk, while no eff ect was recorded in milk protein content. (C) 2000 Elsevier Science B.V. Al l rights reserved.