Sheep are highly susceptible to copper toxicity/poisoning. Copper is stored in the liver following uptake by the body, from where it can be accessed, as necessary, by the animal.

However, there is a limit to the amount of copper that the liver can cope with. If this is exceeded, there is a massive release of copper into the blood leading to destruction of the red blood cells.

Cause

In general, copper toxicity is brought about by either the injection (acute toxicity) or the ingestion of a toxic dose of copper. In terms of the diet, acute toxicity can occur if sheep are fed cattle concentrates by mistake or dosed with cattle boluses. Chronic toxicity can also occur if the sheep (or occasionally cattle) are fed an excess of copper over a prolonged period of time. A high carbohydrate diet will lead to acidic conditions in the rumen, which facilitates the absorption of copper. Therefore, copper toxicity can occur even when sheep concentrates are fed at higher levels.

Symptoms

In mild cases, sheep may have pale mucous membranes due to anaemia. Severely affected sheep have jaundice, red-coloured urine, weakness and thin, watery blood due to the damage to the red blood cells. Most sheep progress on to recumbency with resultant death in almost all cases. In acute toxicity, vomiting and sudden death may also be observed. The disease can be confirmed by testing copper levels in the liver.

Treatment

There are limited treatment options for copper toxicity and treatment is usually futile in most cases. Treatment involves the use of copper chelators, such as ammonium molybdate or sodium thiosulphate, together with supportive care.

Prevention and control

Copper toxicity can be prevented by carefully monitoring the feed levels of copper in sheep diets, as well as taking great care with copper supplements and injections.