Oak and Acorn Poisoning in Horses

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Last updated on
4 min read

Key takeaways

Oak trees are common in North America, and their leaves and acorns are toxic to horses when ingested in large amounts.

  • Toxicosis is rare, but is more common in spring when new leaves bud, and in autumn when acorns are abundant
  • Symptoms of oak and acorn toxicosis include loss of appetite, diarrhea, and colic
  • Oak and acorn poisoning may be life threatening once symptoms develop
  • Diagnosis involves a physical examination, blood work, urinalysis, and stomach lavage to identify leaves or acorns in the ingested feed
  • Treatment includes activated charcoal, fluid therapy, and medications to protect the intestinal lining
  • If caught early, removal of leaves and acorns from the horse’s stomach may prevent toxicosis
  • Prognosis is guarded if symptoms develop
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A closer look: Oak and Acorn Poisoning in Horses

Most horses prefer other food sources, and only consume oak if no other forage is available. Rarely, some horses develop a preference for oak and actively seek out oak leaves or acorns if they are available.

Risk factors

Oak and acorn toxicosis in horses is rare, although it is more common in North America. Horses must consume a large amount of oak leaves or acorns to cause toxicosis, however the mortality rate is high. If a horse starts to develop symptoms, it is always considered a medical emergency.

Possible causes

Oak and acorn toxicosis is caused by the consumption of a toxic dose of oak leaves and acorns, most commonly in spring when leaves grow, or in autumn when acorns fall. Oak contains toxins that damage the kidneys and intestinal tract.

Main symptoms

Testing and diagnosis

A detailed history of the horse, including whether the animal has had access to oak trees, can help identify the cause of symptoms.

Diagnostic tests include:

  • Physical examination
  • Blood work
  • Urinalysis
  • Stomach lavage to identify oak leaves or acorns

Steps to Recovery

Treatment is largely supportive. Treatments include:

  • Activated charcoal and laxatives to reduce toxin absorption
  • Fluid therapy to flush the toxin from the kidneys
  • Medications that protect the intestinal linings

If caught early enough, removal of acorns and leaves from the stomach through stomach lavage can prevent toxicosis.

Note: it is not safe to administer activated charcoal at home. Horses with symptoms of toxicosis need urgent veterinary care. Always administer supplements and medications under guidance of a veterinarian.

The prognosis for oak and acorn toxicosis is guarded once symptoms develop. If the horse survives, recovery may take 2 months or longer. Oak and acorn toxicosis causes kidney damage, so renal function monitoring throughout the recovery period is important to optimize long-term outcomes.


Oak and acorn toxicosis is prevented by restricting access to oak trees. Horses do not typically prefer oak leaves or acorns to other food sources. Ensuring that a pasture has access to other food is often sufficient to prevent animals from seeking oak trees or acorns.

Horses that seek out oak leaves or acorns for consumption may require additional preventative measures. Removing trees from property, or fencing around them to deny access is ideal. Limiting access to oak trees on neighboring properties may also be beneficial.

If complete avoidance of oak trees is impossible, prompt clearing of fallen acorns during autumn is important, as is clearing low branches that a horse might otherwise reach.

Is Oak and Acorn Poisoning in Horses common?

This toxicosis is a rare condition in horses. Oaks are especially common in North America, so it is more common there, but still rare.

Typical Treatment

  • Activated carbon/charcoal//laxatives can help reduce toxin ingestion if administered before onset of symptoms
  • Removal of leaves/acorns in stomach
  • Fluid therapy


Barry R. Blakley , DVM, PhD, - Writing for Merck Veterinary Manual
Barry R. Blakley , DVM, PhD - Writing for Merck Veterinary Manual
No Author - Writing for HorseDVM
CYNTHIA GASKILL, DVM, PHD, DIPLOMATE ABVT - Writing for Practical Horseman

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