Icterus and jaundice are synonymous terms for the yellowing of the whites of the eyes (sclera), gums (mucous membranes) and nonpigmented skin caused by a build up of bilirubin in the blood and tissues.

Bilirubin is a breakdown product of the old fragile red blood cells. This waste product circulates to the liver where it is further processed (conjugated) and mostly excreted out the bile ducts into the intestines. This conjugated bilirubin is converted by anaerobic bacteria to urobilinogen and most makes its way out the intestine in the feces. In the cases of both the conjugated bilirubin and urobilinogen, small amounts are picked up by the blood supply and excreted out the kidneys.

This article examines the causes of icterus in horses, ways to differentiate them, and their significance. Links are then provided to specific diseases that discuss the specific diagnosis, treatment, prognosis, and prevention of those diseases.

A mild icterus, without other signs of disease or secondary to any condition that causes a horse to reduce or stop eating. Though not well understood it probably represents a delayed emptying through the bile duct and curing the cause of the reduced appetite will also fix the icterus.