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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Saturday 9th July 2011

What a difference a fortnight makes. Two weeks ago, our trip to Edinburgh led me to write about Heracleum mantegazzianum because, though not as bad as last year, it was still in evidence. This time, yesterday’s trip revealed plenty of Senecio jacobaea, ragwort, along the roadside and on patches of open ground.

Senecio jacobaea, common ragwort

There are people who say that what you see is Senecio squalidus, Oxford ragwort, and claim that this is all from an original escape from the Oxford Botanical Gardens some time ago. I don’t agree with that and nor does the UK government whose 2004 ‘Code of Practice on How to Prevent the Spread of Ragwort’ specifies that it is referring to Senecio jacobaea.

Separating the two is relatively simple because the Senecio squalidus is much smaller, only reaching about 25cm tall, and flowers in April rather than the summer months. And, because it is believed to have spread itself along the railway lines, you are more likely to find it on embankments and land close to the railway.

But it is the Senecio jacobaea, common ragwort, that is meant when people talk about the problems ragwort can cause. Ragwort Awareness Week, which runs from 11th – 17th July, is a campaign run by the British Horse Society aimed at getting the public to report sightings, so that it ‘can then hopefully use this to lobby for better enforcement of the existing laws or even for new legislation’.

It is rather surprising that the BHS thinks there may be a need for new legislation since it was the driving force behind the existing legislation. In 2002, it supported a Private Member’s Bill intended to revise the 1959 Weeds Act. In the event, the government recognised the need for action and co-operated in the creation of an entirely new piece of legislation called the Ragwort Control Act 2003. This act required a Code of Practice for dealing with common ragwort. The intention being that a failure to follow the code, which was introduced in July 2004, could be taken as evidence of an offence under the Weeds Act.

Senecio jacobaea, common ragwort

Most of the time it is impossible to be definite about the harm done by poisonous plants. With Senecio jacobaea, however, it is possible to state unequivocally that ingestion kills horses. The plant contains pyrrolizidine alkaloids that can cause complete liver failure.

Where that simple fact loses its way, however, is in the way in which horses come to ingest ragwort. The BHS survey of ragwort growing where animals are grazing is a complete waste of time, in terms of actually reducing the incidence of ragwort poisoning. The key fact that is generally overlooked by campaigners against ragwort is its appalling taste. It is one of the most sour things I have ever tasted. Chewing half a leaf was enough to make me never want to taste it again.

It is well-established, both empirically and by scientific studies, that animals will not eat ragwort as long as there is other grazing available. Only if ragwort is the only fodder on offer will animals resort to eating it. I wrote ‘animals’ because it is not just horses who could be poisoned by ragwort. It would kill cattle in just the same way so the fact that there is not a campaign being mounted by the National Farmers’ Union and you don’t hear about cattle dying from ragwort poisoning ought to be enough to suggest that grazing on the plant in the open is not the route to poisoning. In fact, I regularly pass a field that, year after year, has ragwort growing in it and cattle grazing on the other fodder. Farmers are businessmen and would not leave cattle at risk of death if that risk actually existed.

Senecio jacobaea, common ragwort

At this point there will be those who say they know of horses who did eat living ragwort and died soon after. Pyrrolizidine alkaloids are cumulative in their effect so it is possible that a small ingestion of living ragwort could be enough to top up the total dose to its fatal level. I met someone who said she had been ill for several days after simply pulling up a few ragwort plants with her bare hands. Further enquiry revealed that she had suffered severe liver damage from a chemical spillage some years previously making her susceptible to problems from hepatotoxic substances.

It must also be considered that someone responsible for a horse that dies may not want to acknowledge the truth about how the death occurred. Because, another important point about ragwort is that it retains its toxicity after the plant has died. But not its taste. Any ragwort in a field being used to produce hay can, if not removed before harvesting, end up incorporated in the hay where it will be ingested by horses without any problems of palatability.

Reputable producers will, like the pea farmer I wrote about on 6th June, inspect their crop immediately before harvest and remove any ragwort so that their hay is perfectly safe to eat. It is the less reputable grower, or the smallholder who doesn’t know enough to recognise the danger, who allows ragwort to end up in hay. What the British Horse Society should do, rather than trying to whip up public pressure based on incomplete information, is to educate horse-owners not to be tempted to buy cheap hay from unreliable sources.

The answer to the problem of ragwort poisoning in horses lies with horse owners not with increased enforcement of the Weeds Act or a campaign aimed at making the public believe that ragwort growing anywhere should be condemned.