Black Walnut Tree

(Juglans nigra)

Black walnut, which is poisonous to horses.

Plant Description

The black walnut tree is a tree that often grows between 70-100 feet tall, though in wooded areas it has been seen as tall as 150 feet.

Geographic Locations

The black walnut grows throughout the eastern United States. It is usually found in bottomlands, and other areas with rich, moist soil. It has a green fruit that is a few inches in diameter which can be broken open to reveal a brown nut.

Toxic Plant Components

The entire tree is toxic: roots, leaves, bark, nuts.

Toxicity Cause and Symptoms

This is one of the few plants that is not toxic when eaten. Instead, it is toxic when your horse's feet come in contact with it. The exact toxic compound in the tree is unknown.

The usual method for your horse's hooves to come in contact with black locust is if the shavings in your stalls contain black walnut. Shavings that contain as little as 10% black walnut can cause problems.

Because of this it is essential to always know where your shavings are coming from, and if you get them from a saw mill to explain to the personnel why you cannot have any black walnut in your shavings.

Another way for your horse to come into contact with black walnut is if these trees border your pasture. When the nuts fall in the autumn, they can easily fall into pastures, since the tree grows so large.

The only symptom of black walnut tree poisoning is laminitis. It may come on quickly, or it may slowly develop, depending on how much black walnut your horse has come into contact with.

Cure and Treatment

The cure is to treat the laminitis symptoms, and to prevent poisoning to begin with, ensure that your horse has no access to black walnut on the ground. If there are trees bordering your pasture, ensure that you remove your horse from the pasture during autumn and remove the nuts from the ground.

We had a black walnut in one of our small pastures for years and never had an issue, as we would remove the horses from the pasture at the beginning of autumn, and keep them out until the next spring. This saved us from having to pick up all the nuts (it was an extremely large and prolific tree, which is why we didn't cut it down in the first place), as they were gone by the time the horses came back in the spring.

Any time there was a storm, we also promptly removed the horses and picked up any nuts before returning them to the pasture.

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