Mucosal barrier function and microbial community of small intestines in sheep in response to dietary energy concentrations.

The intestinal barrier and local immune response in ruminants are closely related to dietary energy concentration. To determine the optimal dietary energy concentration for the intestinal health of sheep, we compared microbiota, barrier function, and mucosal immunity in the small intestine of sheep consuming diets with different metabolisable energy (ME) concentrations. Forty-five growing Yunnan semi-fine wool sheep, aged 10 months and weighing 30.8 ± 1.9 kg, were randomly allocated to five treatments, each receiving diets with ME concentration of 8.0, 8.6, 9.2, 9.8 and 10.4 MJ/kg DM. After 45 days, sheep were slaughtered for intestinal barrier and microbiota investigation. As dietary energy concentration increased, a linear decrease was observed in the proportion of acetate (P = 0.01) and acetate: propionate ratio (P = 0.02) in jejunum contents, while the proportion of propionate (P = 0.01) increased linearly. Meanwhile, the concentration of the proteins Claudin-7 and zonula occludens-1 increased linearly (P < 0.01) in each of the duodenum, jejunum and ileum tissues. The concentration of mucin-2 and lysozyme in the small intestine tissues also increased linearly (P < 0.01). Additionally, the concentrations of Interleukin-10 (P < 0.01) and Transforming growth factor-β1 (P < 0.01) in the duodenum tissues, as well as secretory Immunoglobulin A (SIgA, P < 0.01) and Interleukin-10 (P = 0.01) in the jejunum tissues exhibited a linear increase. With the increase in dietary energy concentration, the relative abundance of Saccharofermentans in the jejunum decreased linearly (P < 0.001), negatively correlating with the Claudin-7 concentration (r < -0.60). Conversely, the relative abundance of Romboutsia and Succinivibrio in the jejunum and ileum increased linearly (P < 0.001), and were positively correlated with the concentration of Claudin-4, Claudin-7 and SIgA (r > 0.60). The findings suggest that elevating dietary energy concentrations improved the physical, chemical, and immune barriers of the small intestine in sheep, potentially related to alterations in the intestinal microbial community structure. The optimal ME concentration for achieving these benefits was found to be above 10.4 MJ/kg DM.