Alterations in Bile Acid Profiling in Large White Pigs during Heat Stress

Heat stress can reduce productivity through changes in feed intake, fat deposition and total tract digestibility of dietary fat. Bile acids are critical for dietary fat digestion and new roles in metabolism and endocrinology have been demonstrated recently. The objective was to investigate the alterations in plasma and gut bile acids profiles induced by heat exposure. Nine litters (3 pigs/litter) of male Large White pigs weighing 40.8 ± 2.7 kg were assigned to each of control kept at 23°C (CON), heat stress kept at 33°C (HS), or pair-feeding group (PF) kept at 23°C but given the same amount of feed as the HS group. On d 21, the average daily feed intake and average daily gain of the HS pigs was reduced to 55.6% and 41.2% of the controls (P < 0.05), respectively, and the rectal temperature was 0.8°C higher (P < 0.05). By using the LC-MS/MS, 15 bile acids were quantified. When compared with the CON, plasma taurocholates, including tauroursodeoxycholate (TUDCA) and taurohyodeoxycholate (THDCA), were reduced in the HS and PF groups (P < 0.05), but other bile acids did not differ from the CON group. The ratio of taurocholate to glycocholate (T:G) was reduced from 0.1 in the CON to 0.05 in the HS group (P < 0.05) and 0.04 in PF group (P < 0.05). In the ileum, where bile acids were reabsorbed and recycled, reduced TUDCA and glycoursodeoxycholate (GUDCA) was found in the PF group (P < 0.05) compared with the HS group. The T:G ratio was reduced from 0.46 in the CON group to 0.38 in the HS group and 0.27 in the PF group (P < 0.05). In the cecum, ursodeoxycholic acid (UDCA) was higher in the PF and HS groups than the CON group. The T:G ratio was reduced from 0.16 in the CON group to 0.08 in the HS group and 0.02 in the PF group. The HS group tended to have greater taurocholates compared with the PF group (P = 0.08). Our data clearly showed that reduced feed intake during heat exposure has profound impacts on the conjugation process of bile acids. Due to its protective role in endoplasmic reticulum (ER), the observed changes in UDCA conjugation could influence heat-induced oxidative stress.