In a mast year like this one, there’s a bumper crop of all kinds of nuts and fruit. When this coincides with a period of limited grass growth – as we’ve experienced this year – horses are more likely to seek out and eat things outside their normal diet. Unfortunately, acorns are in particular abundance, and if consumed in excess, they can be fatal.
Acorns and oak leaves contain high levels of tannins. When horses metabolise these compounds, they form by-products that bind to proteins in cell membranes, damaging and altering their function. This leads to severe inflammation of the gut and kidneys, resulting in diarrhoea, dehydration, and potentially organ failure.
The number of acorn poisoning cases varies from year to year – similar to atypical myopathy – likely due to environmental factors that we don’t yet fully understand.
Susceptibility varies between individuals. Some horses seem able to tolerate small amounts of acorns, while others may show signs of toxicity after consuming far fewer. Because of the potential for fatal poisoning, it’s safest to limit access to acorns and oak leaves as much as possible.
While mild cases can recover with supportive treatment, severe cases are extremely difficult to treat and often cause intense pain and distress.
Be alert for the following signs, especially if your horse has access to oak trees:
Access to acorns or oak leaves – you may see fragments of acorn shell in the droppings.
Loose droppings or diarrhoea – bloody diarrhoea is particularly concerning.
Colic symptoms – such as restlessness, pawing, rolling, or looking at the flank.
If you notice any of these signs, contact your vet immediately. Early intervention can be lifesaving.
You can help protect your horse from acorn toxicity by taking a few simple precautions:
Move horses away from oak trees if possible. If not, ensure plenty of supplementary forage to reduce their interest in acorns.
Monitor droppings for acorn husks – this can help you assess how many acorns your horse might be eating.
Consider calcium hydroxide supplementation – one study in calves found a protective effect when calcium hydroxide was added to forage in situations of excessive acorn consumption.
Always speak to one of our equine vets before adding supplements so we can advise on the correct amount for your horse.
If your horse is showing any signs of colic, diarrhoea, or appears dull or dehydrated, please call Hook Norton Equine Vets right away. Acorn poisoning can progress rapidly, and prompt veterinary attention gives the best chance of recovery.
Hook Norton Equine Vets: Caring for your horses throughout the seasons, with expert advice, rapid response, and genuine care.
