High grain diet feeding alters ileal microbiota and disrupts bile acid metabolism in lactating dairy cows

Abstract

Bile acids play an important role in the regulation of lipid metabolic homeostasis, but little is known about their metabolism in dairy cows fed a high grain (HG) diet. In the present study, we examined the bacterial community, bile acid profile, and the FXR/FGF19 signaling pathway in the ileum and liver to investigate the gut microbe-BA metabolism interactions response to HG diet and the changes in the subsequent enterohepatic circulation of dairy cows. The results showed that the ileal bacterial community was altered, with an increase of Paraclostridium, Anaerobutyricum, Shuttleworthia, Stomatobaculum in the relative abundance in the HG group. Moreover, Real-time PCR showed that the abundance of total bacteria and bacterial bile-salt hydrolase (BSH) genes was increased in the ileal digesta in the HG group. Meanwhile, HG feeding also decreased the total bile acid content in the digesta of jejunum and ileum and in feces. HG feeding altered the bile acid profile in the ileal digesta by increasing unconjugated bile acids and decreasing conjugated bile acids. In addition, the intestinal FXR/FGF19 signaling pathway was activated. The expression of CYP7A1 (cholesterol 7α-hydroxylase) was depressed, which inhibited bile acids synthesis in the liver of cows fed HG. Overall, HG feeding altered the ileal bacterial community and bile acid profile, and activated FXR/FGF19 signaling pathway, resulting in a decrease of bile acid level in the ileal digesta via the inhibition of hepatic bile acid synthesis. The findings provided novel insights into understanding the relationship between gut microbiota and the homeostasis of bile acids in dairy cows fed a HG diet.