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Ragwort Poisoning in Horses

Ragwort is highly toxic to horses and ponies and should be dug up and removed from grazing pasture.

The abundant bright yellow flowers of the common ragwort (Senecio jacobaea) seem to be everywhere at the moment – certainly in Hertfordshire ragwort seems to be flourishing to a markedly greater extent than in recent years. Ragwort is toxic to horses and ponies and must be removed from pasture as a matter of priority. Ideally the young green rosettes should be identified and dug up in the spring, but the mature, upright plants with clusters of yellow flowers we see at this time of year should also be dug up at the roots.

Danger lurks in poor quality hay and haylage

Ragwort has a bitter taste and is unappealing to horses and ponies who are only likely to eat the plant if pasture is meagre. Fortunately this summer has been quite wet in most parts of the country and the grass is good. But, as we move into August and September, grass pasture can deteriorate rapidly and clumps of yellow ragwort standing tall in brown fields will eventually attract hungry horses. An even greater danger lurks in poor quality hay or haylage containing dried ragwort, which is much more palatable to horses.

Poisoning and dangerously reduced liver function

In horses and ponies, the poisonous pyrrolizidine alkaloids present in ragwort cannot be processed by the liver and will accumulate, compromising the liver cells. Over time the loss of functioning liver cells seriously reduces liver function. Outward clinical signs are frequently not evident until significant loss of liver function and often, by the time the poisoning is diagnosed, it is too late for effective treatment.

Symptoms and diagnosis of ragwort poisoning

Symptoms of ragwort poisoning depend to a great extent on the horse or pony’s length of exposure to the plant and its toxins. Symptoms include lethargy, weight loss, diarrhoea, colic, depression, skin lesions from photosensitisation and odd behaviour with head pressing, aimless walking, circling and seizures. The abnormal behaviour results from the severely compromised liver failing to process and remove the toxins from the blood. The remaining poisons spread throughout the horse to the brain, resulting in the atypical behaviour, known as hepatic encephalopathy.

Diagnosis is made on presentation of clinical signs in conjunction with a blood test and, if a liver problem is highlighted, liver ultrasonography and a biopsy will confirm if ragwort poisoning is evident. Not all liver problems are caused by ragwort poisoning and usually the biopsy will be the technique which secures a definitive diagnosis.

Treatment of ragwort poisoning

Ragwort poisoning is non-reversible, and treatment is given only to support and care for the affected animal. Dietary changes and vitamin supplementation can help in management, but the key to dealing with ragwort poisoning is not to let it happen in the first place – there is no safe level of ragwort consumption!