Autumn alerts

Oaks and sycamores are stalwart trees, but both pose risks to horses in the shape of acorn toxicity and atypical myopathy respectively.

- Angela Jones MRCVS and Karen Coumbe MRCVS explain

IF you've noticed the ground littered with acorns this autumn, you're not imagining it. This year is what's known as a "mast year", and oak trees across the UK have produced a bumper crop of acorns. While that's fantastic news for squirrels and other wildlife, it's far less welcome for horse owners.

A mast year is a natural phenomenon that occurs every few years, when oak trees (and other nut-bearing species) increase their seed production, flooding the environment with an abundance of acorns.

Scientists believe this is nature's insurance policy: by producing vast numbers of seeds in one go, trees overwhelm the animals that usually feed on them, ensuring at least some acorns survive to grow into new trees.

This year's weather delivered exactly the combination needed for that to occur, namely a warm, dry spring and summer, leading to one of the heaviest acorn falls many regions have seen in recent memory.

THE DANGER POSED BY ACORNS

ACORN toxicity occurs when horses ingest acorns, oak leaves or young shoots. Normally, horses avoid eating them because of their bitter taste, but when grazing is sparse, they may show interest. There are even suggestions that some horses may acquire a taste for them.

The toxic compounds in acorns are mainly tannins, which can cause severe damage to the gut and kidneys.

The exact toxic dose isn’t known, and not all horses are affected equally, which makes predicting risk particularly challenging. Some horses may eat small amounts with no ill effects, while others can become gravely unwell after consuming relatively few.

Sadly, in severe cases, acorn toxicity can be fatal.

Historically, the problem was well recognised. In the New Forest, for instance, pigs have long been turned out during autumn to eat up the fallen acorns before the native ponies could ingest them.

RECOGNISING THE SIGNS