Ragwort poisoning is one of the most common causes of plant poisoning in equines; with young horses and ponies most at risk. It is a common weed that grows throughout Ireland. Also known as Senecio jacobea, it contains the toxic compounds pyrrolizidine alkaloids. It is a highly poisonous plant if eaten. Horses are particularly susceptible to ragwort poisoning although other grazing animals, including cattle, deer, goats, pigs and chickens are also at risk. Pyrrolizdine alkaloids principally damage the liver, resulting in severe disease and in many cases death.
The poisonous substances in ragwort are toxic alkaloids. These cause the liver to accumulate copper, causing ill heath and death. On good pastures horses tend to avoid eating ragwort, as it is unpalatable, but they must have an alternative source of good food to graze on. This can therefore be a problem on sparse, overgrazed pastures which ragwort can thrive on.
The poisonous material contained in ragwort is not destroyed by drying. Hay containing ragwort is particularly dangerous. Grass silage containing ragwort is also a serious source of poisoning. Cases of poisoning occurring in late winter and spring often result from the feeding for some months previously of hay or silage cut from ragwort infested swards.
Ragwort loses its bitter taste when cut or wilted (during hay or haylage making) and becomes more palatable to horses. Hay and haylage are common sources of ragwort poisoning as drying does not destroy the toxins.
Ingestion of the pyrrolizidine alkaloid toxin contained in ragwort typically results in the delayed onset of chronic, progressive liver failure. Liver failure is a slow and painful death. Most horses affected by ragwort poisoning die after suffering for periods varying from a week to several months. Liver failure (or hepatic failure) occurs when the liver can no longer perform its essential functions. Liver failure only tends to happen when at least 80% of the liver has been damaged. The liver is able to regenerate under certain conditions. The effects of ragwort toxins are cumulative, thus it is common for ragwort poisoning to occur following consumption of small quantities of the plant over a long period of time. Development of disease can be delayed from four weeks to six months after eating the plant. Different individuals appear to have different susceptibilities to the toxin.
Ragwort poisoning – clinical signs
The clinical signs of equine ragwort poisoning usually only become apparent when liver failure has already occurred. Some horses and ponies might show some signs of slight illness initially, but generally the symptoms develop quite suddenly. Diagnosis can be aided by laboratory analyses of blood samples or performing a liver biopsy to look for any signs of liver damage in the horse.
Early signs include loss of appetite and weight loss, diarrhea, depression and excessive sensitivity to sunlight (photosensitisation), and mild jaundice. More severe signs include a range of abnormal behavior and can include compulsive walking, circling, and head-pressing (such as against a wall) and apparent blindness as well as extreme depression. These neurological symptoms are due to the toxic effects on the horse’s brain
- Unusual behavior, restlessness and uncoordinated movement due to the harmful effects of the toxins on the horse’s brain.
- Photosensitisation – inflammation of white, un-pigmented areas of the skin when they have been exposed to sunlight. This is not the same as sunburn.
- Loss of condition.
- Weight loss.
- Dull coat.
- Poor appetite.
The first and most obvious thing to do is to remove all traces of ragwort from the horse’s diet and environment. Consult your veterinary surgeon who will discuss the latest available treatments. However successful treatment is difficult once signs of ragwort poisoning have become evident as liver failure may have already occurred.
Supportive therapies can be tried in the hope that the liver will regenerate. Feed the horse a healthy diet with easily digestible proteins and a high carbohydrate level which does not place too much demand on the liver.
Unfortunately in many cases the liver is too damaged for this to occur, although some horses can survive. The best treatment is prevention. Learn how to recognise the plant so that you can remove and control it effectively to ensure that your horse does not eat this poisonous plant.