Effects of recombinant bovine somatotropin on goat milk yield, composition and plasma metabolites

Ten multiparous lactating Alpine or Saanen goats were used to test the effects of recombinant bovine somatotropin (bST) on galactopoiesis and metabolism. Treated goats were injected daily with 5 mg bST during 28 d. Supplementation with bST significantly increased yields of milk, fat, and protein compared with controls (28.6, 41.6 and 23.7%, respectively). Voluntary feed intake was not increased. During the first week of treatment, percentage of fat was increased (+ 4.2 g/kg; P 0.10). The proportion of long-chain fatty acids in milk tended to increase in wks 1 and 2, but the trend was reversed in wks 3 and 4. Yields of milk fatty acids were higher for goats in the bST-treated group, particularly for the long-chain fatty acids in wks 1 and 2 (P < 0.05) and the short-chain fatty acids during wks 3 and 4 of bST supplementation (P < 0.01). When regression residuals were used, individual variations in response to bST were noticed (from 13 to 40%; P < 0.05).