Owners are being warned to keep an eye on horses grazing in fields with oak trees due to a bumper crop of acorns this autumn.

In August, a 20-year-old stallion was put down after he was tethered to an oak tree in St Albans, Herts, and suffered liver damage from gorging on acorns.

“As the horse was tethered, it was a snack in great supply,” said an RSPCA spokesman.

Acorns are palatable but can poison horses, so they should be cleared from grazing areas.”

Dr Timothy Farewell, an environment expert at Cranfield University, told H&H recent weather patterns are responsible for high acorn yields.

“We had a warm summer last year, then a harsh winter,” he said. “That produced ideal conditions for lots of flowers to grow on trees. And the early summer weather this year resulted in more fruit.”

Horse owner Carol Phillips from Herts added: “My old girl loves acorns and I have spent many a day raking them up.”

And around 200 pigs have been put out into the New Forest, earlier than usual to clear the acorns so ponies can’t eat them.

H&H veterinary adviser Karen Coumbe says readers should not be unduly worried, but should be aware of the risk.

Oak may cause poisoning, but it is very unusual,” she said. “Most horses will not eat acorns but if grazing is limited or horses get a taste for them, then it is a potential problem, especially green acorns.

Abdominal pain, depression and/or diarrhoea and constipation can indicate poisoning. If a horse seems unwell, have a vet check it out.”

This news story was first published in the current issue of Horse & Hound (29 September, 2011)