Ragwort poisoning: one bite doesn’t hurt?

By: Esther Hegt  and Dr. Pieter B. Pelser ( University of Canterbury- Biological Sciences, Christchurch, New Zealand)

Common ragwort and all other ragworts and groundsels growing in the Netherlands contain compounds that are poisonous to most vertebrates and insects (1). These secondary metabolites are called pyrrolizidine alkaloids (PAs). In plants, these substances are stored in their non-toxic form, but after the plant has been eaten, chemical processes in the intestines and liver transfer these PAs into a toxic form that can damage the liver and, to a lesser extent, also other organs such as kidneys and lungs (2, 3). In contrast to what is commonly thought, PA's don’t accumulate in an animal’s body. In fact, they are usually excreted in about 24 to 48 hours (3) (please see our separate webpage for more information on pyrrolizidine alkaloids and their metabolism). But even in the short time they pass through an animal’s digestive system, PA's can damage the liver in such an extent that an animal can get ill and sometimes even dies. So, Ragwort poisoning can be deadly, but can one bite already be dangerous? The answer to this question depends on how you define the word ‘dangerous’.

Even a single bite of Ragwort can cause liver cells to die and repeatedly eating this plant can result in liver failure, which could eventually kill an animal (1, 3). According to the literature, a diet consisting of 1-10% Ragwort can be lethal in time (4). But although every bite of Ragwort may cause liver cells to die, this doesn’t mean that eating a bite of Ragwort once in a while has a lasting effect on an animal’s health. This is because, up to a certain extent, healthy liver cells take over the function of damaged liver cells (5).  If the damage caused by PA's, however, is too large and liver capacity is reduced with 50-70%, an animal will develop symptoms of liver disease. It is therefore very important to find out where the threshold lies. In other words, how much Ragwort can an animal eat before this will affect its health? Unfortunately, at present there’s no conclusive answer to this question. According to the literature, an amount of 50 to 200 grams of dried Common ragwort per kilogram body weight can be deadly for a horse (6), but it is unclear over what period of time this need to be eaten to be deadly.

In conclusion: does it hurt to eat one bite of Ragwort? Yes: it can damage the liver. Does one bite automatically have a permanent effect on an animal’s health? No, unless an animal frequently eats Ragwort over an extended period of time.

(1) Fu, P. P., Q. Xia, G. Lin & M. W. Chou. 2004. Pyrrolizidine alkaloids - Genotoxicity, metabolism enzymes, metabolic activation, and mechanisms. Drug Metabolism Reviews 36: 1-55.
(2) Stewart, M. J. & V. Steenkamp. 2001. Pyrrolizidine poisoning: a neglected area in human toxicology. Therapeutic      Drug Monitoring 23: 698-708.
(3) Chojkier, M. 2003. Hepatic sinusoidal-obstruction syndrome: toxicity of pyrrolizidine alkaloids. Journal of Hepatology 39: 437-446.
(4) Vos, J. H., A. A. J. Geerts, J. W. Borgers, M. H. Mars, J. A. M. Muskens & L. A. van Wuijckhuise-Sjouke. 2002.     Jacobskruiskruid: bedrieglijke schoonheid. Tijdschr. Diergeneesk. 127: 753-756.
(5) De Lanux-Van Gorder, V. 2000. Tansy ragwort poisoning in a horse in southern Ontario. Can. Vet. J. 41: 409-410. (6) Goeger, D.E., P.R. Cheeke, J.A. Schmitz & D.R. Buhler (1982). Toxicity of tamsy ragwort (Senecio jacobaea) to goats. Am. J. Vet. Res. 43(2): 252-254.