Understanding Jaundice in Meat Inspection

Jaundice (icterus) is a condition characterised by the excessive accumulation of the bile pigments bilirubin and biliverdin within the body's tissues. Understanding the different types of jaundice and their causes is important during meat inspection, as they may indicate underlying disease and influence the final disposition of the carcase.

Bilirubin and biliverdin pigments are produced in the liver, spleen and bone marrow and are normally excreted by the liver in the bile.

Jaundice is the presence of these pigments in excessive quantities within the body.

Three basic types

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

Prehepatic jaundice occurs following excessive destruction of red blood cells. Tick-borne diseases such as Babesia and Anaplasmosis commonly cause this type of icterus.

Hepatic jaundice occurs due to direct damage to liver cells caused by systemic infections or chemical and plant poisoning.

Obstructive jaundice occurs when the drainage of the bile pigment bilirubin is blocked from entering the intestine, causing it to pass into the lymphatic system and bloodstream.

Pigments such as bilirubin and biliverdin are normally produced in the liver, spleen and bone marrow and excreted in the bile. If there is an obstruction to the normal flow of bile (e.g. gallstones), these pigments pass into the lymphatic system and bloodstream. Small amounts of bilirubin may be excreted through the kidneys; however, excessive amounts can permeate the body, causing white connective tissues, fat and cartilage to become yellow.

Obstructive jaundice can be caused by:

• Bile duct blockage by calculi or parasites (liver fluke). Ascaris worms are a common cause in pigs.
• Narrowing of the lumen of the bile duct.
• Mechanical pressure on the bile duct caused by neoplasms, diseased hepatic lymph nodes, hydatid cysts or contraction of fibrous tissue following cirrhosis of the liver.
• When bilirubin oxidises, it is converted to biliverdin, producing a green discolouration of cartilage and white connective tissues. Although the colour differs, both yellow (bilirubin) and green (biliverdin) pigmentation are classified as jaundice.

Disposition

In determining true jaundice, examine the carcase under natural lighting or under artificial lighting with good colour-rendering properties.

To apply an appropriate disposition, assess the following tissues for greenish-yellow, lemon or orange discolouration:

• xiphoid cartilage (if incised, the cartilage will appear yellow)
• joint fluid
• kidney medulla

To differentiate between obstructive and haemolytic jaundice, assess the following organs:

• spleen for enlargement
• liver for pathology
• gallbladder for pathology and enlargement

The carcase and its carcase parts are condemned where there is evidence of:

• pronounced greenish-yellow, lemon or orange-yellow discolouration of the superficial visceral or kidney fat, serous membranes and connective tissues; or
• parenchymatous degeneration of the organs.

A carcase showing jaundice to a lesser degree should be retained and chilled under secure conditions. The carcase and its parts are condemned if, on reinspection, the discolouration has not dissipated to a degree considered acceptable. If the colour has dissipated, the carcase and its parts may be passed as fit for human consumption.

Note: Jaundice should not be confused with the normal yellow colouring (carotene pigmentation) of the fat in older cows and certain dairy breeds such as Guernsey and Jersey cattle. Livers from slaughtered cows frequently show a physiological orange-yellow discolouration. However, the liver should be condemned where excessive parenchymatous degeneration (evidenced by marked friability of the organ) is present. Fatty infiltration is one example.