Effects of heat stress on the response to metabolic challenges in growing pigs

Abstract

Heat stress (HS) decreases feed intake but unexplainably increases plasma insulin parameters in a variety of animal models. Whether HS alters post‐absorptive carbohydrate and lipid metabolism in growing pigs is unknown. Seven crossbred gilts (53±6 kg BW) were subjected to 2 periods: thermoneutral (TN; 20°C, 36% RH) for 4d, and HS (32°C, 23% RH) for 8d. All pigs received an intravenous glucose tolerance test (GTT) on d2 of TN and d1 and 6 of HS; and an epinephrine challenge (EC) on d3 of TN and d2 and 7 of HS. Heat stress increased rectal temperatures (P<0.01; 39.4 vs 40.4°C) and respiratory rates (P<0.01; 30 vs 94 bpm), and reduced feed intake by 37% (P<0.01). Heat stress decreased (P<0.05) basal glucose and insulin concentrations by 14% and 50%, respectively. Basal nonesterified fatty acids (NEFA) were initially elevated during HS (92%), but progressively declined to TN levels by d3 (P<0.01). On d1 HS, glucose disposal and insulin response to a GTT decreased (49% and 24%, respectively) compared to TN. By d6 HS, the insulin response remained unchanged, but glucose disposal increased compared to d1 (P<0.01). On d2, NEFA response to an EC did not differ from TN, but was reduced (53%; P<0.01) by d7. Glucose response to the EC did not change over time (P>;0.05). These data suggest that, despite a low plane of nutrition, decreased adipose tissue utilization and increased glucose oxidation might be key acclimation mechanisms to heat stress.