Bile acid from the metabolism of cholesterol from the conversion, the synthesis is divided into three stages: ① primary bile acid synthesis. In the hepatocellular endoplasmic reticulum microsomal enzyme system, in which cholesterol 7α-hydroxylase is rate limiting enzyme, cholesterol after hydroxylation, hydrogenation and side chain breaks and plus coenzyme A and other multi-step reaction, and ultimately the formation of primary cholic acid (bile acid and chenodeoxycholic acid); ② secondary bile acid synthesis. Primary bile acid with bile into the small intestine to participate in the digestion and absorption of lipids, at the end of the ileum, about 95% to 98% of the bile acids are reabsorbed by the portal vein, the portal vein reflux bile acid more than 80% effective intake. About 1/4 of the combined primary bile acid in the jejunum, ileum and colon upper, under the catalysis of bacterial enzymes, and further production of deoxycholic acid, cholic acid, ursodeoxycholic acid and other secondary bile acids; ③ three levels bile acid synthesis.
In short, the use of bile acids can effectively improve the use of animal fat, improve feed conversion, maintenance of animal liver health. The use of bile acids also improves the utilization of oil, maximizes the nutritional value of the oil, and avoids the waste of energy feed. But the following questions remain to be resolved: whether the addition of exogenous bile acids will inhibit the secretion of endogenous bile acids, the optimal addition of exogenous bile acids and the best compatibility, exogenous bile acid is toxic and have side effects.