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Oak Trees and associated management

I have a number of horses in a field where excellent shelter is provided by overhanging oak trees. I understand Oak and acorns are poisonous to horses. Should I face the near impossible job of removing all the leaves, twigs and acorns from the field? How poisonous is Oak and what symptoms should I watch out for?

9/11/06

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Martina Stuart

All parts of the oak tree are poisonous but in practice it is usually either the young sprouting shoots in the spring and the acorns in the autumn that cause problems. The only safe way of dealing with the threat is to keep horses and ponies away from both. This is best achieved by fencing the area off either permanently or temporarily with electric fencing. It is difficult to remove the falling acorns often enough even if the grass below the trees is mown and mechanical equipment is available unless the animals can be removed at times of risk.
That having been said oak trees are very common around horse pastures and cases of poisoning are in my experience relatively rare. Animals will often develop cravings for toxins once they have developed a taste for them and oak is no exception. This addiction can be stimulated by the ingestion of a few leaves or acorns which will have no obvious clinical effect. Fragments of oak leaves in the faeces can sometimes be a warning sign that ingestion is occurring and special precautions can then be taken for that individual.
The toxins produced in the digestion of oak products affect the bowel and kidney function. This can cause either scouring or constipation which I suspect is dose related and if any substantial amount has been ingested lethargy, bloody urine, kidney failure, coma and death can follow.
Lethargy abdominal discomfort colic constipation and diarrhoea are the initial signs (or should it be symptoms) to watch out for.
There is no effective treatment for the kidney damage but the chance of this developing is reduced by keeping any affected horse well (possibly slightly over) hydrated if necessary by intravenous administration. The constipated horse should be treated with plenty of mineral oil (liquid paraffin) water and electrolytes by stomach tube. Electrolyte replacement fluids are also essential for the scoured horse and in either case early veterinary attention is vital.
There is a very good book on plant poisoning published by J A Allen by Keith Allison and Chris Day ?A guide to plants poisonous to horses? obtainable from (www.horseweb-uk.com)

10/11/06

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