By Esther Hegt en Dr. Pieter B. Pelser ( University of Canterbury- Biological Sciences, Christchurch, New Zealand)
All Ragworts (Tribe Senecioneae, Family Asteraceae) growing in the Netherlands contain pyrrolizidine alkaloids of the senecionine type. These substances are toxic for most vertebrate animals and insects (1, 2, 3). If a horse eats it fresh or dried, poisoning will occur (8). Research shows that Ragwort plants when dried, remain toxic for a very long time (4). Horses don't recognize dried Ragwort plants as poisonous (5) and hay which contains Ragwort can thus cause Ragwort poisoning (8, 10, 12). Ragwort plants are sometimes part of the flora of an area where horses are kept, and the horses will have the opportunity to eat ragwort fresh. If and to what extent this happens, is not quite clear.
Different sources indicate that horses eat ragwort fresh (6, 7, 8). Not clear, though, is with what frequency. Especially on internet groups and in the popular media the horse owners are very concerned about their horses eating fresh ragwort with apparently a lot of casualties as a result thereof.
In the popular media there is a tendency to call upon the government to have a more active policy and lawfully force landowners to eradicate ragwort from areas where horses are kept. Other sources, mainly articles in international scientific magazines, state that horses recognise ragwort as poisonous and eat it only in exceptional circumstances (3 ,8, 10, 11, 12). However, in the Netherlands many a horse owner does not believe this statement and in one of the horse magazines (“Bit”) it was called pseudo-science (13). We suppose this distrust is based on horse owners mentioning having seen their horse actually eat fresh ragwort.
The observation of the horse owners are a cause for concern, and maybe the scientific opinion needs to be adapted. To be able to determine how regularly ragwort is eaten fresh by horses, horse owners could be of great help. To make sure the actual plant is indeed ragwort, we have asked horse owners in the Netherlands to send us samples. Out of experience we have noticed that many people are confusing ragwort with other plants, not only when the plant is still a rosette, but also when it is flowering.
(I have made downloadable flyers that should help you to recognise ragwort.) We suggest that you remove the plant, and dry it. A plant expert will be able to determine whether it is ragwort or not. Also photos of what is suspected as ragwort can be sent to us. In this way, we want to verify and map the cases of ragwort eaten fresh by horses in the Netherlands. With the samples and the pictures we can at any stage verify if ragwort gets actaully eaten.
(1) Schneider, D. 1987. The strange fate of pyrrolizidine alkaloids. In: Chapman, R. F., E. A. Bernays & J. G. Stoffolano (Eds.). Perspectives in chemoreception and behavior: Springer, Berlin/Heidenberg. 123-142.
(2) Boppré, M. 1986. Insects pharmacophagously utilizing defensive plant chemicals (pyrrolizidine alkaloids). Naturwissenschaften 73: 17-26.
(3) Macel, M. 2003. On the evolution of the diversity of pyrrolizidine alkaloids. The role of insects as selective forces. Thesis Leiden University.
(4) Pelser, P. B., H. de Vos, C. Theuring, T. Beuerle, K. Vrieling & T. Hartmann, 2005. Frequent gain and loss of pyrrolizidine alkaloids in the evolution of Senecio sect. Jacobaea (Asteraceae). Phytochemistry 66: 1285-1295.
(5) Gezondheidsdienst voor dieren
(6) Smith, D. October - and Ragwort is Killing our Horses. Ragwort-UK Ltd
(7) Ragwort Facts. Information on Common Ragwort from a factual perspective.
(8) Giles, C. J. 1983. Outbreak of ragwort (Senecio jacobaea) poisoning in horses.Equine Veterinary Journal 15: 248-250.
(9) Bokt Paardenforum
(10) Bain, J. F. 1991. The biology of Canadian weeds. 96.Senecio jacobaea L. Canadian Journal of PlantScience.71: 127-140.
(11) Poole, A. L. & D. Cairns. 1940. Botanical aspects of Ragwort (Senecio jacobaea L.) control. Department of Scientific and Industrial Research Bulletin 82: 2-61.
(12) Harper, J. L. & W. A. Wood. 1957. Senecio jacobaea L. The Journal of Ecology 45: 617-637.
(13) Bröckotter, F. 2006. De opmars van Jakobskruiskruid. Natuurbeheer brengt paarden in gevaar. Bit 137: 108-111.
(14) Determinationtopic Planten KruiskruidForum. The KruiskruidForum is closed.