Icterus

Icterus (Jaundice)

Icterus is the result of an abnormal accumulation of bile pigment, bilirubin, or of haemoglobin in the blood. Yellow pigmentation is observed in the skin, internal organs (Fig. 22, 23), sclerae (the white of the eye), tendons, cartilage, arteries, joint surfaces etc. Icterus is a clinical sign of a faulty liver or bile duct malfunction, but it may be also caused by diseases in which the liver is not impaired. Jaundice is divided into three main categories (Fig. 24).

1. Prehepatic jaundice (haemolytic icterus)
2. Hepatic jaundice (toxic icterus)
3. Posthepatic jaundice (obstructive icterus)

Fig. 22: Jaundice of an aged cow caused by liver disease. Note yellow discoloration of body fat, lungs, heart and kidneys.







Fig. 23: Yellow discoloration of pig viscera and carcass caused by cirrhosis of the liver.









Fig. 24: Classification of jaundice

1. Pre-hepatic:
2. Hepatic:
3. Post-hepatic

Prehepatic jaundice occurs following excessive destruction of red blood cells. Tick-borne diseases such as Babesia ovis and Anaplasmosis cause this type of icterus, which is one of the main causes of carcass condemnation in Southern Africa due to prevalence of these parasites. Overproduced blood pigment, which cannot be metabolized in the liver, builds up in the blood (haemoglobinemia). It is excreted by the kidneys into the urine (haemoglobinuria). Normal urine colour changes and becomes bright red to dark red.

Hepatic jaundice occurs due to direct damage to liver cells as seen in liver cirrhosis (Fig. 23), systemic infections, and in chemical and plant poisoning. In sheep, jaundice may have been caused by phytogenic chronic copper poisoning.

Liver function is impaired and the liver is unable to secrete bile pigments. Obstructive jaundice occurs when the drainage of the bile pigment bilirubin is blocked from entry into the intestine. This usually occurs due to the obstruction of the hepatic ducts by a tumour, by parasites such as flukes or by gall stones. Obstruction may also occur due to an inflammation of the bile ducts. In hogs, mature ascarides may occlude the bile ducts.


Judgement :


Animals suspected to have icterus should be treated as "suspects" on antemortem examination. On postmortem examination, the carcass and viscera with haemolytic, toxic icterus and obstructive icterus are condemned. Less severe cases are kept in the chiller for 24 hours. Upon re-examination, the carcass may be approved or condemned depending on the absence or presence of pigment in the tissue. If the obstructive icterus disappears after 24 hours, the carcass and viscera can be passed for human food.

A simple laboratory test will help to make an objective test for bile pigment icterus. Two drops of serum are mixed on a white tile with two drops of Fouchets agent.² A blue/green precipitate is positive for bile icterus.

² Fouchets Reagent Trichloroacetic acid.25 gmFeCl₃ (10 % solution)10 mlDistilled water100 ml

Differential diagnosis :



Yellow fat in animals with heavy corn rations, nutritional panniculitis (yellow fat disease, steatitis) and yellow fat seen in extensive bruises. In yellow fat disease, the fat has a rancid odour and flavour upon cooking.

To differentiate icterus from the normal colour of fat of certain breeds, the sclera, intima of the blood vessels, bone cartilage, liver, connective tissue and renal pelvis should be examined. If yellow discoloration is not noted in these tissues, icterus is not present.

Icterus should not be confused with yellow fat disease in hogs fed predominantly on fish by-products or by the yellowish appearance of tissue caused by breed characteristics or nutritional factors.