PERFORMANCE, CARCASS COMPOSITION, AND BLOOD HORMONES AND METABOLITES OF FINISHING PIGS TREATED WITH PORCINE SOMATOTROPIN IN HOT AND COLD ENVIRONMENTS

Two experiments were conducted to assess the ability for recombinant porcine somatotropin (rpST)-treated pigs to perform and cope with the demands of hot and cold environments. In the first experiment, finishing pigs were exposed to either a thermoneutral (TN; 18 to 21°C) or a hot environ- ment CH; 27 to 35°C) for 35 d. In the second experiment, pigs were exposed to a TN or cold environment CC; 5 to 15°C). The rpST delivered by a 6-wk prolonged-release system had no effect on ADG, whereas both H and C reduced ADG by 29.4 and 11.8%. respectively. In the first experiment, rpST- treated pigs consumed 17.6% less feed than control pigs, whereas rpST-treated pigs in H consumed 24.4% less feed than rpST-treated pigs in TN. Overall feed gain ratios through the first 4 wk of both studies were improved by 21.8 and 14%, respectively, by rpST (P < .05) and were 24.3'2% poorer in C (P < .05) than in H. The changes in blood concentrations of pST, IGF-I, and IGF-I1 associated with rpST were not influenced by the different environments. Total body composition of rpST-treated pigs had increased amounts of protein (P < .05) and decreased amounts of fat (P < .05); H further reduced fat (P < .05). The C resulted in reduced protein content (P < .05). No evidence of thermal imbalance due to rpST was found as assessed by rectal temperature, respiration rate, and heat production estimated by indirect calorimetry and chemical analysis.