Acorn Alert: Why This Year’s Bumper Crop Poses a Serious Risk to Horses

This autumn has brought an unusually large acorn crop, and while it might look picturesque, it’s also proving dangerous for our horses. Many practices have already seen several cases of colic and suspected acorn poisoning linked to horses grazing under oak trees, so now’s the time to be extra vigilant.

Why Are Acorns Dangerous?

Acorns, oak leaves, and even young oak shoots contain tannins, naturally occurring plant compounds that can be toxic to horses when eaten in significant quantities.

Once ingested, these tannins can irritate and damage the lining of the gut and kidneys, leading to symptoms such as:

Colic or abdominal discomfort
Diarrhoea (sometimes dark or black in colour)
Depression and loss of appetite
Signs of dehydration
In severe cases, kidney failure

Some horses seem more inclined to eat acorns than others, often out of boredom, curiosity, or hunger when grazing is poor. The latter is the most common reason this year, following the hot, dry summer weather.

Why This Year Is Worse

We’ve had a bumper acorn crop this year, meaning many paddocks and turnout areas are heavily littered with acorns. We’ve had an exceptional number of acorns this year because 2025 is a mast year, a natural cycle in which oak trees produce a much heavier crop than usual. Combined with a warm, wet spring and a warm summer, conditions have been perfect for acorn growth. As a result, many paddocks are heavily littered with acorns this autumn, increasing the risk of horses accidentally eating them. With grass growth slowing down in autumn, horses may be tempted to browse acorns even if they normally wouldn’t. This combination has led to a noticeable increase in colic and toxicity cases in our area.

What You Can Do

Check fields regularly and fence off areas under oak trees if possible.
Provide plenty of forage. Keeping horses well-fed with hay or haylage reduces the temptation to eat acorns.
Remove acorns from grazing areas where practical (sweeping or raking, using a poop scoop rake flipped over to the flat side makes light work of collecting acorns easily!).
Use temporary electric fencing to restrict access to oak-heavy zones.
Monitor for early signs of colic or illness, and contact your vet immediately if you notice anything unusual.

What To Do If You Suspect Acorn Poisoning

If your horse has eaten acorns and is showing signs of colic, diarrhoea, or dullness:

Call your vet straight away.
Remove the horse from the source of acorns.
Do not wait for symptoms to worsen - early veterinary intervention can make a big difference.

There is no specific antidote for acorn toxicity, but supportive treatment (fluids, pain relief, and gut protectants) can help recovery if caught early.

In Summary

While a few acorns might not cause harm in every horse, the risk of serious illness is real, especially during heavy acorn years like this one. Prevention is far easier (and safer) than treatment, so please take a few minutes to check your fields and keep your horses safe this autumn.

If you’re concerned your horse may have eaten acorns or is showing signs of colic, contact your vet immediately.