Ragwort (Senecio jacobea) is often found in pasture throughout the UK and contains a poisonous substance (toxin). This toxin (Pyrillozidine) causes damage to the liver of a number of animals including horses and donkeys. Most animals tend to avoid eating Ragwort as it is not very palatable. Poisoning generally occurs when horses ingest Ragwort in dried hay, which has been contaminated with the plant. Although if food is scarce or there are a large number of plants present within the pasture, horses may be forced to eat it.

There are two types of poisoning with Ragwort – acute (immediate) and chronic (long term). The acute form is rarely seen as large quantities need to be eaten but when it occurs it is manifested as sudden death.

Chronic poisoning is the most common. The signs of poisoning are usually not seen until 4 weeks to 6 months after eating the plants. Small doses of the poison gradually accumulate in the horse’s liver where it causes damage to the liver cells and scarring. Eventually the liver shrinks in size. The liver has large functional reserves and so it is only once these reserves have been exhausted that signs of poisoning develop. These signs can often come on suddenly, although in some horses and ponies mild illness can precede more severe symptoms. Signs of chronic disease include loss of appetite, depression, diarrhoea, weight loss, sensitivity to sunlight and jaundice (yellow colour to skin or eyes). The liver is responsible for filtering the blood of many substances so when it stops functioning correctly these compounds can affect the brain. Animals can develop neurological symptoms such as weakness, circling and head pressing.

Ragwort is a biennial plant, which in its first year forms flat rosettes. In the second year it becomes much taller and produces yellow flowers. The only reliable method of prevention is to remove the weed from pasture. The plants should be pulled up by their roots and disposed of away from livestock. It is important to ensure that animals have no access whatsoever to any plants even dried as they can still be poisonous. The poison can also be absorbed through the skin of humans so it is important that impervious gloves are worn. Plants on adjacent land should be removed to avoid the spreading of seed back into your paddocks. Always ensure that there is adequate grazing or alternative food sources such as hay, so that your horse or pony is not tempted to eat any ragwort, which may have been missed. Sprays are available for the control of ragwort and advice can be sort from your local farm merchant on appropriate ones for you.

There is a DEFRA Code of Practice to prevent the spread of ragwort. Those who disregard the need for the weed’s control do face prosecution by the government (Ragwort Control Act 2004)