Acorns and therefore Oak trees are poisonous to horses. This is most commonly seen in the autumn months when grazing is at a premium.

Toxins present:

  • Gallic Acid 
  • Tannic Acid

Can cause damage to kidneys, intestines and liver if the acorns, the branches and leaves are consumed. 

Clinical signs are related to the organs they affect:

  • Depression
  • Colic
  • Diarrhoea
  • Loss of appetite
  • Mouth ulcers
  • constipation/impaction colic
  • Bloody urine
  • incoordination/wobbly – ataxia


  • Usually based on clinical signs as there is no specific test to detect this
  • History of grazing near Oak trees especially in autumn


Symptomatic depending on the clinical signs the horse presents with

Some horses can become addicted to the taste of oak leaves and acorns therefore it is important that these animals are kept away from these trees, using methods such as electric fencing.