Acorn Poisoning in Horses

Anna O'Brien, DVM
Written by:
Published: March 2, 2012
Acorn Poisoning in Horses

Do Oak Trees Pose a Health Risk to Your Horse?

While many animals in the wild depend on the acorn for their nutritional needs, the acorn poses a toxicity risk to some animals, including horses, cattle, goats, and sheep. Although cattle are much more sensitive to the toxins in acorns than horses, large amounts of ingested acorns can induce severe illness. This is due to the tannic and gallic acids in the acorn, which can cause severe damage to the gastrointestinal system and kidneys.

Symptoms and Types

  • Constipation
  • Anorexia
  • Colic (pain in the abdomen)
  • Blood in the urine
  • Kidney damage
  • Dehydration
  • Fluid accumulation in the legs (edema)


Acorn poisoning is caused by the ingestion of large amounts of acorns, oak leaves, or branches. Many times acorns are ingested by accident, and in small amounts they are harmless, especially when combined with the normal roughage of hay and grass. There is anecdotal evidence that some horses develop a liking bordering on addiction for acorns and will actually seek them out, overindulging to the point of illness.


Diagnosis can be difficult unless the horse has an obvious history of acorn ingestion. Occasionally, acorn remnants can be found in the horse’s manure.


There is no antidote for acorn poisoning. Activated charcoal has been known to be an effective treatment for acorn poisoning, if given immediately after acorn ingestion, as it can absorb toxins in the gut and allow them to be excreted from the system.

As dehydration is a common sign of acorn toxicity, IV fluid therapy is often warranted. This will help combat fluid loss from diarrhea and help ward off impending renal failure. IV fluid therapy can also help support the horse’s circulatory system and assist in the prevention of shock in severe cases of acorn toxicosis.

Living and Management

After heavy winds or a storm there may be so many oak leaves and acorns on the ground that your horse will eat enough of them to cause a toxic effect on its system. Some horses will develop an extreme liking for acorns and oak leaves, and will wait for them to fall from the tree, to the extent that other foods will be disregarded.


The only way to protect your horse from acorn poisoning is by fencing off oak trees and keeping your horse out of the wind-path of falling acorns and leaves. If there are oak trees near the fence line of your horse’s pasture, it is a good practice to clear fallen branches after a storm.

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