Black Walnut tree in horse pasture

Asked September 28, 2015, 12:20 PM EDT

I am purchasing a home that has a mature single black Walnut tree in a pasture I plan to use primarily for horses but also possibly at times sheep. I have heard mixed information on leaving it, removing it etc. I would prefer not to loose the section of pasture where the tree is located, but need to make sure it is safe for the animals. thank you

Marion County Oregon

1 Response

There is no easy answer to your question as there are many factors at play with the Black Walnut tree. The roots, leaves, bark and nuts contain a substance called Juglone, which is a plant growth inhibitor. However, the actual toxin which causes problems in horses, sheep and goats is still not completely known and understood. Regarding horses, the main concern is using shavings/bedding containing black walnut fiber. The black walnut shavings contain a toxin which causes rapid onset (24-48 hours after contact) of laminitis. As little as 5% black walnut in the bedding can cause laminitis. The main problem appears to be contactual based with toxic residue from bedding getting on the feet and legs. Laminitis has also been observed in sheep and goats exposed to Black Walnut in bedding.
The consumption of the leaves and nuts in the fall can cause digestive upset (colic). I think there is so little known about the toxin that researchers have not yet determined whether there are more severe toxic effects such as kidney failure from the consumption of leaves, bark and nuts.
The pollen in the spring has also been related to horse and human allergies.
The nuts, in the fall on the ground, can develop a mold which if consumed by dogs can lead to seizures.
There are so many things that can go wrong with Black Walnut that I would be very leery in having it in a pasture. If you were to have it removed it would have to be done very carefully as all sawdust and debris would have to be removed and the area would need to be fenced off for a period of time while everything diluted or composted to reduce risk of exposure to the toxin.
If the tree is left in the pasture a high level of management would need to be used in removal of horses when nuts and leaves are falling. Or the removal of tree debris in the case of a storm.
This is a difficult situation in all aspects. Please feel free to give me a call to discuss this further.