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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Tuesday 6th September 2011

Prof Derek C Knottenbelt, BVM&S, DVM&S, DipECEIM, MRCVS RCVS is the European Specialist in Equine Internal Medicine, Philip Leverhulme Equine Hospital, Leahurst, Neston, part of the University of Liverpool. Or, rather that should be ‘was’ because in an email from him today he twice pointed out that he is retired. Unfortunately, that wasn’t clear from a letter he wrote to the Yorkshire Post about liver disease in horses and the University of Liverpool website says that, 'following a very short retirement, Derek is now back in the Equine hospital continuing from where he left off'.

Prof. Knottenbelt is often quoted, by the horse owning community, as THE authority on ragwort poisoning so his views deserve careful consideration. That is why, when some of the comments made in his letter looked a little less than scientifically rigorous, I decided to ask him some direct questions by email.

Before going on, I thought I should say that at the bottom of this blog post is a photograph of a very ill horse that Professor Knottenbelt has given me permission to reproduce. We’ll get to that later but I didn’t want it to be a complete shock.

There were many comments in the letter that I felt were based on questionable facts but I am not intending to make an ad hominem attack. Rather I want to explain why I believe the conclusion the professor reaches, that Jacobaea vulgaris, common ragwort, is a plant that should be eradicated, is not the way to end the suffering of animals, whatever the extent of that suffering is.

My first concern about Prof. Knottenbelt’s letter was that he gave a rather loose figure for the number of deaths from liver failure due to poisoning seen in his clinic stating that it was ‘more than 10 per year’ and that he felt that this suggested a countrywide figure of not less than 1,000. But he went on to say that the BHS’s discredited estimate of 6,000 plus is ‘possibly high or possibly not’.

This seemed like a straightforward point to explore so I emailed to ask him;

‘Would you be kind enough to provide me with the actual number of deaths due to liver failure in each of the last five years?
‘Would you also tell me how many of those deaths due to liver failure were the result of pyrrolizidine alkaloid poisoning?
‘Of those, how many were proved to be the result of the ingestion of Jacobaea vulgaris, common ragwort?
‘And, in those cases, was the route of administration of the poisons determined and, if so, what were the routes found?’

The professor was kind enough to answer very quickly but, unfortunately, he wasn’t able to answer any of these questions. He said that the ‘more than 10’ was a ‘rough guide’ but went on to state that this was an underestimate. I really don’t know how he can be sure that a number that is only a ‘rough guide’ is underestimated but it seems he is. He also said that being retired he was not in a position to find the information I wanted. I've asked the University of Liverpool to clarify Prof. Knottenbelt's current status as, clearly, it and he cannot both be correct.

Jacobaea vulgaris (Senecio jacobaea), common ragwort

Of course, with no precise figures for deaths my other questions become redundant though Prof Knottenbelt did point out that ‘It is quite unrealistic to assert categorically that every bit of damage in every horse is due to one species of Senecio since PA’s exist in many other plants’. I’ll return to that point.

He went on to acknowledge ‘It is well known that RW in hay and haylage etc is the biggest risk’ but said that cases do arise from horses eating ragwort from their pasture and he sent me a photograph of a horse in very poor condition and showing signs of liver damage from PA poisoning to illustrate his argument. The animal had to be destroyed and the owner was prosecuted for cruelty, though unsuccessfully.

I asked to be able to show that photograph here because there are some who say that ragwort is never any danger in pasture and I agree with Professor Knottenbelt that the picture shows that this is not the case. But, it must be said, one photograph cannot be used to attempt to justify the claim that horses do eat living ragwort regardless of the general state of the pasture.

Where I completely disagree with him, however, is where the blame lies for this incident and the how ever many others there are like it. In his email, he says ‘The horse had been in the paddock for 14 months’. He says that there was ‘adequate grass sward in other areas of the field’ but the horse, nonetheless, grazed on the ragwort. As I say on the plant page for Jacobaea vulgaris, animals are known to develop tolerance of and preference for grazing ragwort. If an animal is forced to eat ragwort because there is no other food available they will continue to eat it once returned to good pasture. The fact that the professor saw ‘adequate grass sward’ does not mean that the horse had not been obliged to eat ragwort at some time in its fourteen month residence.

The professor uses this case as an argument in favour of eradicating ragwort but, to me, if the horse had been in ragwort-bearing pasture for fourteen months that indicates a very poor quality of care by the owner. Rather than contacting DEFRA to complain about the plant, which is what most of the horse lobby suggests, the proper course of action is, surely, to contact the RSPCA about the neglect apparent from the conditions in which this horse was kept.

It does seem that there is a general aversion in the horse-owning community to accepting that some of those people who keep horses don't do a good enough job. I suppose it is possible that such an entrenched position is an unconscious response to the extreme views of those animal activists who maintain that all animal 'ownership' is by definition cruel.

I said I would return to Professor Knottenbelt’s comment that ‘It is quite unrealistic to assert categorically that every bit of damage in every horse is due to one species of Senecio since PA’s exist in many other plants’. That being so, there is clearly no prospect of completely eradicating all PA bearing plants and so to pick on just one, Senecio jacobaea or Jacobaea vulgaris as it should now be called, is illogical and unhelpful.

To me the situation is analogous to the general situation with poisonous plants and children. You cannot expect to keep your children away from poisonous plants so you have to act to minimise the possibility of their coming to harm. With horses, as I’ve said many times but feel I should repeat, it is up to the owners to provide adequate pasture and safe conserved forage. If anyone believes they know an owner who is not doing that then they should bring the matter to the attention of the RSPCA, not blame a plant.


A horse suffering liver damage