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Acorn Poisoning

If eaten, acorns, leaves and branches from oak trees pose a risk of poisoning to horses.

  • Last reviewed: 30th May 2022
Branch 3682386 Branch 3682386

Fortunately, acorn poisoning is rare in horses, but it does have years where an increase is seen, potentially due to the increased crop of acorns. So, it is important to know what we can do for our horses to minimise the risk.

It has long been known that acorns are poisonous to horses (cattle and dogs too)1, 2, 3 they contain a substance called “tannic acid2” which when eaten in sufficient quantity (this may be different for each individual horse) the tannins can cause liver and kidney damage, droppings containing blood, colic and diarrhoea. It is rare that acorn poisoning happens as acorns are bitter tasting. However, there is an increased risk of horses eating them if pasture is poor and there is little availability of good quality forage. It is important to remember that some horses, regardless of taste, quality of grazing or even extra forage, will seek out acorns. Anecdotally, these horses appear to develop a liking for the acorns that borders on addiction although science is yet to prove this4.

Acorns And Oak Leaves

What increases the risk?

  • Some horses are naturally more susceptible to acorn poisoning, a small amount may make them ill.
  • Overgrazed paddocks or long hot summers reducing grazing quality increase the chance of horses eating acorns.
  • An increase in acorn fall after strong winds or storms.

How can I reduce the risk?

Avoid using the field until the acorns can be raked or vacuumed off the ground. If this is not an option, provide good quality forage away from the oak trees to reduce the likelihood that the horses will eat them. Alternatively, set up electric fencing around the tree, ideally to the branch span; so that the horses cannot get to the acorns.

What are the signs?

Some horses will have a higher level of tolerance to acorns and will show no symptoms at all. Others may eat just a few and become sick. Signs include:1, 2, 4, 5

  • Acorn husks in droppings
  • Depression
  • Dehydration
  • Lethargy, not moving around as much as normal
  • Reduced appetite
  • Increased lying down
  • Colic
  • Diarrhoea containing blood
  • Constipation
  • Mouth ulcers

What are the treatments?

There is no specific treatment for acorn poisoning and the care given to your horse will depend on the number of acorns eaten, and the stage of illness. Intravenous fluids will help wash out the toxins and prevent further damage to the organs. To stop damage in the intestines activated charcoal, mineral oil or paraffin may be administered by your vet. Pain killers may be given if the horse has colic symptoms but encouraging the horse to eat hay and drink water will also help dilute the toxins6.

What do I do if I suspect acorn poisoning?

If you suspect your horse may have eaten acorns, leaves or parts of the tree call your vet immediately and they will be able to advise the best course of action for your horse.


1. Anderson, G. A. et al. (1983). Fatal acorn poisoning in the horse: pathologic findings and diagnostic considerations. Journal of American Veterinary Medicine. 182 (10) 1105-1110.

2. Smith, S. et al. (2014). Suspected acorn toxicity in nine equines. Equine Veterinary Journal.47(5):568-72

3. Bonnevay,E. (2020). Are acorns edible? And other acorn facts. Woodland Trust.

4. Pet MD. (2012). Acorn Poisoning in Horses.

5. XLVets. (2020). 110 Acorn Factsheet.

6. Kentucky Equine Research. 2020.Answer Exchange.