Effect of supplementing a Bacillus subtilis-based probiotic on performance, intestinal integrity, and serum antioxidant capacity and metabolites concentrations of heat-stressed growing pigs

Abstract Exposing pigs to heat stress (HS) seems to modify the intestinal microbiota which may compromise the integrity of the small intestine epithelia. Probiotics, live microorganisms, can help pigs to maintain a healthy intestinal environment. Eighty pigs (21.6 ± 3.4 kg body weight) exposed to HS or thermal neutral (TN) conditions were used to evaluate the effect of a Bacillus subtilis-based probiotic on performance, body temperature, and intestinal integrity. Treatments were: TN pigs fed a control diet without (TN-C) or with 1 × 106 CFU probiotic/g of feed (TN-P), and HS pigs fed a control without (HS-C) or with probiotic (HS-P). The control diet was formulated with wheat, soybean meal, and free amino acids (AA). Feed and water were freely available during the 21-d study. At completion, samples from duodenum, jejunum, and ileum were collected to analyze epithelial histology and tight junction protein expression; antioxidant activity, and free AA and metabolites in serum. Relative abundance of Lactobacillus, Bifidobacterium, Escherichia coli, and Bacillus in ileal content was analyzed. Ambient temperature in the TN room ranged from 19 to 25 °C, and in HS room from 30 to 38.5 °C. Intestinal temperature in HS-P pigs was lower than in HS-C pigs. Weight gain and feed intake reduced, but feed:gain and respiration rate increased in HS compared to TN pigs, regardless of diet (P < 0.01). Probiotic increased weight gain and improved feed:gain (P < 0.05) in both TN and HS pigs, but feed intake did not differ. Heat stress decreased villi height in jejunum and villi height:crypt depth in duodenum and jejunum (P < 0.05). Probiotic increased villi height in duodenum and ileum, and villi height:crypt depth in all small intestine segments (P < 0.05). Relative abundance of Lactobacillus and Bifidobacterium tended to reduce, and E. coli tended to increase (P < 0.10) in ileal content of HS-C pigs. Ileal relative abundance of Bacillus was higher (P < 0.01) in HS-P pigs than in HS-C and TN-C pigs. Cystathionine, homocysteine, hydroxylysine, α-amino-adipic acid, citrulline, α-amino-n-butyric acid, P-Ser, and taurine were higher in HS than in TN pigs (P < 0.05). These data confirm the negative effect of HS on performance, body temperature, and intestinal integrity of pigs. These data suggest that supplementing 1 × 106 CFU probiotic/g of feed based on Bacillus subtilis DSM 32540 may help to counteract the negative effects of HS on the performance and intestinal integrity of pigs.