Copper toxicity in sheep

PRODUCTION ADVICE - APRIL 2020 - ANIMAL HEALTH

By Mark Corrigan
District Veterinarian
P: 02 6051 2208 | M: 0428 256 431 | E: mark.corrigan@lls.nsw.gov.au

The late summer, and early autumn rain has brought summer weeds such as heliotrope, caltrop and hairy panic. These weeds are known to cause photosensitisation in stock.

They also have the potential to cause chronic copper toxicity. Sheep readily accumulate copper in their livers. These weeds contain the toxin pyrrolizidine alkaloid (PA), which causes liver damage. Once the liver is damaged, it can increase the storage of copper to excessive levels.

At some point, weeks or months after grazing these weeds, the copper can be suddenly mobilised from the liver into the circulating blood. This causes mass destruction of red blood cells, a haemolytic crisis, resulting in jaundice (yellowing of carcass - see photo, right), haemoglobinuria (red urine, containing haemoglobin, from destroyed red blood cells) and death. British breed and cross-bred sheep are more susceptible to copper poisoning than merinos.

The trigger for this copper release is sufficient damage to the liver, but it is also made more potent by stress, caused by things such as shearing, or a dramatic increase in copper in the diet.

Some plants such as subterranean clover are known to be high in copper. Dietary copper will also be high where molybdenum and sulphur are deficient. Copper toxicity is possible purely due to dietary excess, but pre-existing liver damage from ingestion of plants containing PA is a common occurrence in this area.

Clinically, the sheep show lethargy, depression, recumbency (lying down) and weakness. Gums and the ‘whites’ of the eyes turn yellow, and at post-mortem there is a generalised jaundice, and the liver turns bronze-coloured and damages easily with the presence of dark red urine in the bladder.

Treating a clinically affected animal is unrewarding. Treatment of an affected mob aims to remove stored copper from the liver before it is released into the bloodstream, causing the haemolytic crisis. Please seek veterinary advice if you have issues with dying or jaundiced sheep. Vets will be able to advise on treatments such as a molybdenum drench to decrease liver copper stores as well as ruling out other diseases that have a similar presentation.