Acorn Poisoning in Horses

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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.