Will Black Walnuts Hurt Horses?

Is it dangerous for my horse to graze near areas with black walnut trees and walk through fallen walnuts?

will black walnuts hurt horses
Remove moldy walnuts from pastures and other areas horses can access, because the nuts could contain a fungal toxin. | Photo: iStock

Q.We have a ton of black walnut trees lining our paddocks and pastures—the trees themselves are not in the pastures or within the horses’ reach, but the branches overhang the fences, and the walnuts fall to the ground into the enclosures and the lanes between them. I know that standing in, eating, or lying in black walnut shavings can cause horses to develop laminitis, but I’ve heard that that these shavings generally come from the trunk part of the tree. What about grazing near these trees and walking through the fallen walnuts? Also, what about branches that fall in the pastures. Is there any danger for my horse?

—Lynn, Versailles, Kentucky

A.It is well-established that horses bedded on wood shavings that contain 20% or more black walnut shavings can develop the hoof disease laminitis. There is little if any concrete evidence that horses grazing under walnut trees or walking in walnut leaves develop laminitis. However, a hungry horse that has little to eat except walnut leaves, fallen walnuts, or branches that have fallen into the horse enclosure may be at risk. Always remove moldy walnuts from pastures and other horse areas, because the nuts may contain a fungal toxin.

Remove fallen branches and fruit of walnut and butternut trees from horse pastures. Also prune walnut branches that horses can reach, and even fence off walnut trees where horses may have a habit of chewing the bark.


Written by:

Anthony P. Knight, BVSc, MS, Dipl. ACVIM, is a professor of large animal medicine in the College of Veterinary Medicine and Biomedical Sciences at Colorado State University. He received his veterinary degree from the University of Nairobi, Kenya, in 1968. After completing a master’s degree at Colorado State University, he joined the faculty in 1974. His current professional interests include livestock heath, foreign animal diseases, emergency management, and plant toxicology. He has written two books on poisonous plants of animals in North America, and maintains a poisonous plants website for use by anyone wanting poisonous plant information.

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