Black walnut toxicity

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Black Walnut Toxicity

Black walnut (Juglans nigra) is a large tree which is often planted as an ornamental or for its hardwood value. Wood shavings used for bedding for horses that contain as little as 20% of black walnut wood will cause laminitis in horses. Close association with walnut trees while pollen is being shed (typically in May) may cause horses to develop allergy symptoms. There have been reports of horses experiencing colic and respiratory distress after chewing on the bark of black walnut trees.

Toxin responsible

The chemical responsible for black walnut toxicity in horses is juglone, which is a natural phenolic compound produced by the tree. The toxin is thought to be absorbed through the horse's coronary band and skin while they are standing on shavings. Horse owners also need to take caution when using wood chips in pastures, for drainage or landscaping, as these products can sometimes be produced by black walnut trees.

Clinical signs

Clinical signs of black walnut toxicity (relating to laminitis) usually develop in affected horses within 8 to 18 hours after exposure to the toxin.


Bounding pulse
Shifting weight to the hind limbs
Odd stance
Lower leg swelling
Respiratory distress


  • History - recent arrival of new bedding material
  • Clinical signs
  • Laboratory tests
  • Radiographs



Removal from the source
Treatment for secondary complications
Supportive care


  • Only purchase wood shavings from reputable suppliers.
  • Make yourself aware of the weeds and plant species that can be invasive in pastures and/or poisonous to horses.
  • Take periodic walks around pastures to check for the presence of potentially poisonous plants
  • Check that hay does not contain dried up poisonous plants
  • If you borrow or hire farm machinery ensure it is clean prior to arriving on your property, the same goes for lending of your own equipment.
  • Quarantine new animals in a separate paddock the first 10 days to 2 weeks after arrival. Weed seeds can be passed through an animal's digestive tract.


Better than for other causes of laminitis.

Scientific Research

General Overviews

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Risk Factors

  • Purchasing low quality wood shavings for use as bedding
  • Using wood chips or landscaping materials containing mulch in horse pastures for drainage improvement methods or within reach of horses in pastures.