Effects of low feed intake and hot environment on plasma profiles of glucose, nonesterified fatty acids, insulin, glucagon, and IGF-I in lactating sows

This experiment was designed to compare the effects of high ambient temperature and of feed restriction on plasma hormones and metabolites in primiparous lactating sows. Females were exposed to a constant thermoneutral (20 degrees C) or hot environment (30 degrees C) during lactation. Sows housed at 30 degrees C were given free access to feed (30AL: n = 12), whereas those housed at 20 degrees C were either pair-fed with those at 30 degrees C (20RF: n = 6) or were fed ad libitum (20AL: n = 6). A jugular vein catheter was surgically inserted in all sows at 100 d of gestation. Absorption of nutrients during the meal induced significant increases in plasma glucose, insulin, and glucagon, and a decrease in nonesterified fatty acids on Day 19 of lactation and Day 1 postweaning (P < 0.05). On Day 19, feed restriction at 20 degrees C was associated with higher plasma glucagon before the meal, lower plasma insulin after the meal and a lower insulin-to-glucagon ratio (I/GA) before and after the meal (P < 0.05). On Day 19, mean plasma concentrations measured in 30AL females were between those measured in 20AL and 20RF sows for nonesterified fatty acids and glucagon before feeding, and for glucose, nonesterified fatty acids, insulin, and glucagon after feeding. None of the differences between the 30AL and the 20RF groups was significant (P < 0.1). On Day 19, the only significant differences between the 30AL and 20AL groups were observed after the meal for plasma insulin and I/GA. Plasma insulin-like growth factor-I increased after farrowing in 20AL and 30AL sows only (P < 0.05). It was higher in 20AL than in 20RF and 30AL sows on Days 4 and 19 of lactation (P < 0.05). Overall, underfeeding at 20 degrees C induced changes in plasma insulin, glucagon, I/GA, and insulin-like growth factor-I, which would favor gluconeogenesis and body-reserve mobilization during lactation. Differences in glucagon and I/GA before the meal between well-fed sows at 20 degrees C and heat-exposed sows were attenuated, which could have detrimental consequences on glucose availability to the mammary gland and hence on milk production at 30 degrees C.