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Acorn poisoning in horses

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

  • Last reviewed: 19th September 2022
Branch 3682386 Branch 3682386

Are acorns poisonous to horses?

If eaten, acorns, leaves and branches from oak trees pose a risk of poisoning to horses1,2,3. Fortunately, acorn poisoning is rare in horses due to the bitter taste, but some years we see it more frequently, potentially due to a larger crop of acorns.



Acorns And Oak Leaves
Acorns and Oak leaves

Acorns contain a substance called tannic acid2, which when eaten in sufficient quantity (this may be different for each individual horse) the tannins can cause serious illness.  

What increases the risk of acorn poisoning?

  • Some horses are naturally more susceptible to acorn poisoning, a small amount may make them ill4
  • Overgrazed paddocks or long hot summers reducing grazing quality and lack of forage increase the chance of horses eating acorns
  • An increase in acorn fall after strong winds or storms
  • Some horses, regardless of taste, quality of grazing or even extra forage, may seek out acorns — there’s anecdotal evidence that some horses develop a liking bordering on addiction for acorns and will actively seek them out5

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?

  • 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

Lethargic Horse

How do you treat acorn poisoning in horses?

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 charcoal4, 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 have concerns for your horse, call your vet and they’ll be able to advise the best course of action.


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. XLVets. (2020). 110 Acorn Factsheet.

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

6. Kentucky Equine Research. 2020.Answer Exchange.

Get in touch – we’re here to help 

The Horse Care and Welfare Team are here to help and can offer you further advice with any questions you may have. Contact us on 02476 840517* or email – you can also get in touch with us via our social media channels. 

Opening times are 8:35am-5pm from Monday–Thursday and 8:35am-3pm on Friday. 


*Calls may be recorded for monitoring purposes.