Hello, I have a question regarding the toxicity of black walnut skins...

Asked November 6, 2017, 9:38 AM EST

Hello, I have a question regarding the toxicity of black walnut skins ingested by horses. I do know the shavings used in or found in in horse bedding is toxic but what about the black walnuts themselves? Especially the hulls and in particular the green outer hull once it has started decomposing. Recently a family of squirrels has been leaving these in my horses waterers. Of course I panicked! I am now dumping and cleaning them day and night. Are these black "rinds" toxic? HELP! Barbara

Carroll County Ohio black walnut toxicity

1 Response

Thanks for your question about the toxicity of various black walnut plant parts, Barbara. This Rutgers Extension article indicates that:

"Since the bark and nut hulls from the black walnut are toxic, these trees should be removed from horse pastures as a precaution."

Other resources appear be less conclusive about shell toxicity, but this article says:

"Horses and ponies can contract acute laminitis, an inflammation of the foot, where black walnut wood chips or sawdust is used for stall bedding. Acute laminitis and high respiratory rates in horses and ponies has also been reported where stables and paddocks are located too close to walnut trees. Pollen shedding from walnut trees can cause allergic reactions in people and horses.

Husks of fallen walnuts can become toxic to livestock, and lethal to dogs if ingested due to a mycotoxin called 'Penitrim A', which is produced by Penicillium mould. Therefore, walnut nuts showing symptoms of decomposition, such as a brown or black rotten appearance in the husks, may leak toxin into the kernels and are not fit for human consumption."

Finally, as this Professor explains in an earlier AaE question:


"Black walnut is toxic to horses when the inner wood comes into contact with their hooves. This is why black walnut shavings should not be used as horse bedding. There is some concern with the actual walnuts, however, this is rare and not much is know about the interaction of horse ingesting the nuts. There is actually more concern for your pasture grass. Black walnut roots excrete a chemical that inhibits grass and other plants from growing under and around the tree. Because of this, we do not normally recommend planting black walnuts in or around a pasture. For more information, go to http://www.extension.umn.edu/horse/components/poisonousplants.htm Thank you. Krishona Martinson, PhD Univ. of Minnesota."

So, it would appear the the better course is to remove both the trees and scout for the husks diligently, lest they injure your horses. Hope this is helpful. Good luck!