The walnut tree, also known as the Juglans nigra, can be extremely dangerous to horses. When the toxin of this tree is allowed to come in contact with hooves and limbs (via shavings in stall bedding), or is ingested by the animal, the results can be quite painful—sometimes even deadly.
Definition of Black Walnut Tree
The black walnut tree ranges in height from 50 to 100 meters. It has darkly pigmented, furrowed bark with feather-shaped compound leaves. The walnut the tree produces is round and roughly 3 to 7 cm in diameter. It will often be surrounded by 20 or so smaller leaves. The toxin that the black walnut tree produces is chemically known as juglone.
Dangers of Ingesting
When the foliage of a black walnut tree is ingested by a horse, one reaction can be severe laminitis, an inflammation of the laminae. The laminae attaches to both the horse's hoof wall as well as its pedal bone, the bone lying directly inside the hoof capsule. The animal is often euthanized not so much because of the systemic toxicity of the juglone, but because painful lameness so often is the result. Aside from laminitis, ingesting it can cause distal edema (swelling of the lower end of the horse's extremities) and dangerously elevated temperatures.
Treatment for Juglone Intoxication
The Ontario Ministry of Agriculture, Food and Rural Affairs states that juglone, which can often be found in shavings used in horse bedding, should be promptly removed. The laminitis that often results can be treated with the use of non-steroidal anti-inflammatory agents, such as Banamine or phenylbutazone (or bute). Often owners can treat the horse's discomfort by running cool water on the animal's limbs, starting within the first hour of juglone exposure. Not only does the cool water relieve some of the limb swelling, but can help to rinse off the juglone that may still be on the skin's surface.
Black walnut trees grow most prominently within the eastern United States, and can often be found in bottomland areas (lower-lying land sitting close to water sources) or other locations where the soil is otherwise richer with more moisture content.
Some veterinarians will often attempt to detoxify the animal's gastrointestinal tract, using mineral oils or activated charcoal. Both activated charcoal and mineral oil help impede absorption of the juglone into the horse's digestive tract and cause the horse to fecally expel the toxin.