Age Differences in Ileum Microbiota Density: VFAs and Their Transport-Related Gene Interactions in Tibetan Sheep

Microbiota density plays an important role in maintaining host metabolism, immune function, and health, and age has a specific effect on the composition of intestinal microbiota. Therefore, the age-specific effects of age differences on the structure and function of the ileum microbiota in Tibetan sheep were investigated by determining the density of the ileum microbiota, the content of VFAs, and the expression levels of their transporter-related genes at different ages. The results showed that the contents of acetic acid and propionic acid in the ileum of Tibetan sheep in the 1.5-year-old group were significantly higher (p < 0.05) than those in other age groups, and that the contents of total VFAs were also significantly higher (p < 0.05) than those in other age groups. The relative densities of ileum Rf, Ra, and Fs were significantly higher in the 1.5-year-old group than in the other age groups (p < 0.05). The ileum epithelial VFAs transport-related genes AE2, MCT-4, and NHE1 had the highest expression in the 1.5-year-old group, and the expression of DRA was significantly lower in the 1.5-year-old group than in the 6-year-old group (p < 0.05). Correlation analysis showed that Cb, Sr, and Tb were significantly positively correlated with butyric acid concentration (p < 0.05) and negatively correlated with acetic acid, but the difference was not significant (p > 0.05); MCT-1, MCT-4, and AE2 were significantly positively correlated (p < 0.05) with acetic, propionic, and isobutyric acid concentrations; NHE1, NHE2, and MCT-4 were highly significantly positively correlated (p < 0.01) with Romboutsia and unclassified_Peptostreptococcaceae, while acetic acid was significantly positively correlated (p < 0.05) with NK4A214_group; Romboutsia, and unclassified_Peptostreptococcaceae were significantly positively correlated (p < 0.05). Therefore, compared with other ages, the 1.5-year-old Tibetan sheep had a stronger fermentation and metabolic capacity in the ileum under traditional grazing conditions on the plateau, which could provide more energy for Tibetan sheep during plateau acclimatization.