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 p orcine somatotropin (rpST)-treated pigs to perform and cope with the d emands of hot and cold environments. In the first experiment, finishin g pigs were exposed to either a thermoneutral (TN; 18 to 21-degrees-C) or a hot environment (H; 27 to 35-degrees-C) for 35 d. In the second experiment, pigs were exposed to a TN or cold environment (C; 5 to 15- degrees-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 ratio s through the first 4 wk of both studies were improved by 21.8 and 14% , respectively, by rpST (P < .05) and were 24.3% poorer in C (P <.05) than in H. The changes in blood concentrations of pST, IGF-I, and IGF- II associated with rpST were not influenced by the different environme nts. Total body composition of rpST-treated pigs had increased amounts of protein (P < .05) and decreased amounts of fat (P < .05); H furthe r reduced fat (P < .05). The C resulted in reduced protein content (P < .05). No evidence of thermal imbalance due to rpST was found as asse ssed by rectal temperature, respiration rate, and heat production esti mated by indirect calorimetry and chemical analysis.