Summary: Short‐chain fatty acids ( SCFA s), particularly butyrate, are known to suppress inflammation, and regulate the gut bacterial ecology. However, little is known about propionate. We report here that propionate infusion in the caecum dramatically affected the structure of colonic microbiota of pigs based on 16s rRNA high‐throughput sequencing. Sixteen pig models were perfused with saline or sodium propionate by a fistula in the caecum. At d 28, all pigs were slaughtered for analysing bacterial metabolites, colonic microbiota and the expression of genes related to inflammation. The results showed that caecal infusion of sodium propionate increased the concentration of propionate and decreased the butyrate concentration in colonic content. For biogenic amines, the tyramine concentration was increased, while the concentration of cadaverine was decreased by infusion of sodium propionate. Furthermore, at the level of phylum, propionate increased the abundance of Bacteroidetes and reduced the abundance of Firmicutes . Prevotella and Bacteroides counts were increased, while Turicibacter abundance was decreased at the level of genus. Real‐time qPCR showed that the expression of NF ‐κB and IL ‐18 was upregulated by propionate infusion, whereas no significant differences were observed for the expression of other genes related to inflammatory processes. Taken together, these results provide a new evidence for the role of short‐chain fatty acid propionate on the composition of microbial community and inflammatory cytokines.

Succinate is a metabolic intermediate of the tricarboxylic acid (TCA) cycle in all aerobic organisms, and is also a vital microbial metabolite in the gut. Although succinate is known to regulate intestinal metabolism and immune function, its role in the protection of the intestinal epithelial barrier function and inflammation is poorly characterized. In this study, we evaluated the effects of succinate on intestinal epithelial barrier function and inflammation in pigs. Twenty-four growing pigs were distributed into three groups (n = 8) and received either a basal diet (control group) or the same diet supplemented with 0.1% succinate or 1% succinate. The diet supplemented with 1% succinate led to alterations in the intestinal morphology. We confirmed in vitro that 5 mM succinate treatment modulated intestinal epithelial permeability by increased transepithelial electrical resistance (TEER) in intestinal porcine epithelial cell (IPEC)-J2 cells. Furthermore, succinate treatment increased the abundance of tight junction proteins claudin-1, zona occluden (ZO)-1, and ZO-2 in the jejunum in vivo and in vitro. In addition, dietary succinate supplementation promoted the expression of inflammatory cytokines interleukin (IL)-25, IL-10, IL-8, and IL-18 in the jejunum. Taken together, these data identify a novel role of succinate in the modulation of intestinal epithelial barrier function, which may be a nutritional target to improve gut health in animals.

Short-chain fatty acids (SCFAs) produced by microbial fermentation facilitate the differentiation and proliferation of intestinal epithelium. However, the role of individual SCFAs, such as propionate, on intestinal development is still unclear. In the present study, sixteen barrows fitted with a cecal fistula were randomly divided into two groups for cecal infusion of either saline (control group) or sodium propionate (propionate group). After 28 days, the length and the relative weight of intestinal segments were calculated, the intestinal morphology was assessed, and the expression of tight junction protein was measured using qPCR and Western blotting. Compared to the saline group, the length of the colon was significantly increased in the propionate group (p < 0.05). The jejunal villi length and villi/crypt ratio in the propionate group were significantly higher than in the saline group (p < 0.05). Furthermore, propionate infusion significantly upregulated the mRNA levels of Claudin-4 and the expression of Claudin-1, Claudin-4, and Occludin protein in the jejunal mucosa (p < 0.05). Collectively, these findings revealed that the short-chain fatty acid propionate in the hindgut contributed to intestinal development, and selectively enhanced jejunal tight junction protein expression.

The gut microbiota plays a vital role in regulating the host’s physiological functions, including metabolism and immunity. The microbial composition and metabolism are modulated by multiple factors; host sex is an important yet under-explored determinant. To investigate the sex-dependent differences in the gut microbiota within the small and large intestine, sixteen somatic mature Jiangshan black pigs (eight males and eight females) were analyzed. The ileal and colonic microbial community and metabolites were profiled using 16S rRNA gene high-throughput sequencing and gas chromatography. Distinct sex-related discrepancies were observed in both the microbial composition and metabolism of the ileum and colon. In the ileum, compared with the male group, the female group exhibited higher abundances of Unclassified Chloroplast and Pseudomonas but a lower abundance of Romboutsia (adjusted p < 0.05). Functional prediction indicated enrichment in amino acid metabolism pathway in females, with more copy numbers of genes encoding key enzymes for propionate (mmdA) generation and elevated valerate levels (p < 0.05). In the colon, compared with the male group, the female group showed higher abundances of Streptococcus, Phascolarctobacterium, and Prevotella spp. and lower abundances of Eubacterium coprostano-ligenes group, Blautia, Christensenellaceae R-7 group, and Ruminococcus (adjusted p < 0.05). Additionally, the female group had more copies of genes mmdA and LcdA (associated with lactate production), along with higher concentrations of propionate and lactate (p < 0.05). Correlation analysis between microbial metabolites and sex-biased bacteria further revealed that the SCFA concentration positively correlated with Prevotella spp. and negatively correlated with Romboutsia, Christensenellaceae R-7 group, and Blautia. Collectively, these findings highlight the pronounced sex-dependent discrepancies in the microbial composition and metabolism within the small and large intestines of Jiangshan black pigs, providing new insights for precisely modulating the microbiota community and metabolism in pigs according to sex.