Ragwort, also known as Senecio jacobea, is a distinctive yellow flowering plant that thrives on wastelands and poor quality pastures. It contains a toxin of a class called pyrrolizidine alkaloids that are hepatotoxic (damage the liver). Ragwort has a bitter taste and most horses will avoid eating it provided there is an alternative source of food, unfortunately when ragwort is cut and wilted it looses its bitter taste but the toxic compounds remain intact. Ingestion of these toxins over time has a cumulative effect causing progressive liver failure.
The liver may be considered as the processing centre of the horse, receiving various chemical components directly from the intestines and converting them in to other substances that the body can utilize. One of the other major tasks performed by the liver is the processing of various toxins, either ingested or produced by the horse’s body. The microscopic structures at the heart of liver function are the hepatocytes; a highly specialized type of cell. The pyrrolizidine alkaloids attack these cells casing them to die off and instead of being regenerated they are replaced by fibrous meaning that, over time, the liver shrinks in size. The liver has a large functional reserve and it typically takes 80% of the organ to become damaged before any signs can be observed.
Signs of ragwort poisoning tend to be similar to other diseases that affect the liver. Often bizarre or depressed behaviour is observed as a result of toxic substances building up in the blood stream that the liver is unable to process thereby effecting the brain. Another common clinical sign is inflammation of white, un-pigmented areas of skin that have been exposed to sunlight. This is commonly known as photosensitization. The chemicals that cause this are found in many green plants including grass and would usually be processed by the liver. However, in liver failure they build up high enough concentrations in the blood stream to then become activated by sunlight and damage the surrounding exposed skin. Other common signs of liver failure are weight loss, diarrhoea and jaundice (yellow staining of tissue).
Since ragwort causes damage to the liver cells many of the substances that would be contained within the hepatocytes leak out in to the blood stream. By sampling blood we can run tests to check the levels of the substances. This process is called biochemistry and we use it to check the function of lots of other things as well as the liver. These values are then compared to normal reference ranges. Interpretation can sometimes be difficult as damage to the hepatocytes may have been occurring very slowly over a long period of time. Once the liver has been tipped over the edge to a state of liver failure there may not be high levels of these substances released into the blood stream. However we can also check for substances that are manufactured by the liver and if these are reduced this inherently indicates a degree of liver failure. Finally to confirm evidence of damage to the liver a biopsy (small piece of tissue) may be taken from the liver using an uktra-sound guided biopsy needle.
Unfortunately there is still not a commercial test available that can be run to identify the toxins from the Ragwort plant and as the clinical signs of ragwort poisoning do not differ greatly from other liver diseases pinpointing the exact cause can often be difficult. It is for this reason that there is much controversy about how many deaths there are per year from ragwort poisoning and many people on the Internet are quick to suggest there is not a significant danger. One thing, however, is for certain: Ragwort does cause some degree of liver damage and is easily preventable. Would you take the chance?
DISCLAIMER: This advice is intended for use by registered clients of Priors Farm only. The advice offered is general advice only. Priors Farm clients who wish to discuss the individual circumstances of their horse should contact the office. To speak to a vet please phone between 8.30 – 10.00 am on weekday mornings.