LIVER DISEASE

Liver poisoning, due to ‘Patterson’s curse’, is one of the most common causes of liver disease in horses in Australia. The plants are not palatable and horses will not usually eat them unless there is little other food available. This year is expected to be a bad one for Paterson’s Curse as the drought conditions have meant both little competition and less alternative food sources.

Unless very large quantities are eaten, signs of poisoning are usually not seen until 4 weeks to 6 months after eating the plants. Long term ingestion results in cumulative damage to the liver. Signs of liver disease only develop when too much of the liver is affected to be able to compensate. Early signs include loss of appetite, signs of depression, diarrhoea, weight loss and jaundice. More severe signs include compulsive walking, head pressing, apparent blindness, photosensitization (sensitivity to sunlight leading to blistering) and convulsions. These behavioural abnormalities are caused by failure of the damaged liver to remove other toxins from the blood. Severely affected cases usually die within ~ 10 days.

The diagnosis of poisoning is based on clinical signs and laboratory tests. A history of ingestion of ‘Patterson’s curse’ is often unclear due to the time lag between ingestion and the development of clinical signs. Blood tests can confirm a diagnosis of liver disease and assess the liver’s ability to function. Liver biopsy may be necessary to confirm Patterson’s Curse style poisoning or suggest other possible causes of liver damage.

As signs often only develop late in the course of the disease, treatment is rarely successful for severely poisoned horses. Although damaged tissue can not recover, less severely poisoned horses can sometimes be helped to compensate with a special diet

Other horses living in the same environment should be tested for liver damage.

Always ensure that there is adequate grazing or alternative food sources, so that your horse is not tempted to eat the poisonous plants. Do not use pastures that are contaminated with these weeds for hay making because the poison remains active even in dried plants. Do not rely on the appearance of the tell-tale purple flowers to know that your paddock is full of Patterson’s Curse as it is the young growing stage that is most likely to be eaten. Spraying can be an effective means of controlling Patterson’s Curse