Bile acid from cholesterol transformation, in three stages: A. Primary bile acid synthesis: cholesterol in the role of a variety of enzymes, after a series of catabolism, and ultimately the formation of a combination of primary bile acid (cholic acid and chenodeoxycholic acid). B. Secondary bile acid synthesis: primary bile acid with the bile into the small intestine to participate in digestion and absorption of lipids, most of the changes are not re-absorbed portal venous blood circulation. About 1/4 of the combined primary bile acids in the jejunum, ileum and colon upper, in the bacterial enzyme catalysis, the further generation of deoxycholic acid, cholic acid, ursodeoxycholic acid and other secondary bile acids. C. Bile acid synthesis: liver cell synthesis of bile acids and glycine or taurine binding, the formation of a combination of bile acids, secretion into the bile duct. 
For young animals, due to the development of the digestive system is not perfect, therefore, lack of synthesis of bile acids, affecting the absorption of fat in the feed. The crustaceans, crabs and other crustaceans because of the lack of synthesis of cholesterol and bile acid in the body's ability, therefore, need to obtain these substances from the bait to maintain normal growth.