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Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Friday 9th September 2011

I’ve never set out to make this site a comprehensive guide to poisonous plants. There are just about 100 plants featured here and some of the books in my libarary have up to 1,200 species so there’s plenty missing.

The selection of plants to include is pretty arbitrary and, to an extent, relies on the plant have interesting folklore, being psychoactive or having recorded incidents of harm that are worthy of note.

By that definition, I should include a very well-known plant that, just this week, has caused an unfortunate death of a horse. The plant is the oak tree of which two of the best known are Quercus robur, the English oak, and Quercus petraea, the sessile oak also called the Welsh oak.

The Herts Advertiser, local paper for the county of Hertfordshire to the north of London, reported that a horse that had been left tethered to an oak tree had been put down after suffering severe liver damage and stomach problems as a result of eating the acorns dropped from the tree.

The Quercus genus contains tannins and phenolic compounds. Poisoning in livestock is usually reported to result from cattle eating young leaves in the spring or acorns in the autumn. It is said to require quite a large amount to be consumed and kidney failure plus stomach problems are, generally, the result.

The story from Hertfordshire says nothing about kidney problems and the books don’t say anything about liver damage but many of the reported symptoms overlap with symptoms of liver failure so, since this is a newspaper report not a scientific paper, I don’t think there’s any reason to doubt the cause of the poisoning.

My ‘go to’ book in cases of animal poisoning is ‘Poisonous Plants in Britain and their effects on Animals and Man’ by Marion Cooper and Anthony Johnson. It was published in 1984 so doesn’t have recent incidents but it notes that many horses can eat acorns without suffering anything worse than a brief period of indigestion.

Based on figures for cattle, the problem appears to come when acorns form the majority of the diet and Cooper & Johnson say that there were 18 cases of cattle poisoning in 1976-77.  The summer of 1976 was, famously, very hot and dry and this resulted in a bumper crop of acorns coupled with a shortage of grazing.

There seem to be no problems over the taste so animals will eat the plant without problem but it has been suggested that there may be an addictive quality that means an animal will continue to eat Quercus once it has started. Since small amounts seem to cause few, if any, problems, it must be assumed that the horse in this incident had feasted on the acorns.

The newspaper report said that the horse had been left tied to the tree, in a charity-run park, for some weeks. The owner had been advised to move it, about a week before it became so ill that it had to be put down, but had not done so.

On 6th September I wrote that there are plenty of plants capable of causing poisoning in animals so the focus on Jacobaea vulgaris, common ragwort, is as illogical as it is hysterical. I had not expected to receive confirmation of that point so soon and in such unfortunate circumstances.