Carotenoid pigments can contribute to yellow color in avian plasma, but controlled studies have not ruled out pathologic contributions to plasma color. Bile acids are synthesized in the liver from cholesterol. In seed-eating birds, chenodeoxycholic acid is the primary bile acid produced. Bile acids are stored in the gallbladder and released after a meal. In non-gallbladder containing birds an increased release has also been documented.
Bile acids assist in digestion and absorption of fats.
A majority of the bile acids are absorbed by the small intestine, transported to the liver by portal veins, and reclaimed by the liver. Elevations in bile acids are associated with reduced hepatic function. Clinical experience with bile acid assays indicate that this procedure is much more sensitive than looking at liver-related enzymes. Enzymes measuring hepatocellular damage will often return to normal after acute insult. Persistent loss of liver hepatic function is better indicated by measuring bile acids.