It’s hard to imagine that a natural part of our environment could possibly be harmful to our horses. However, many plants are not only poisonous, but potentially deadly to horses. Many plants and trees have strong medicinal qualities; early medicines to treat numerous medical conditions–from lowering a fever to stimulating a strong heartbeat–were often derived from plants, shrubs, and trees.
It therefore should be no surprise that the substances in many common trees can be quite poisonous if consumed by our herbivorous friends in raw form. In this article, we will discuss the most poisonous trees, how to identify them, and how to prevent your horse from becoming a victim of their toxic ways.
Black Walnut Tree
One of the most dangerous of poisonous trees is the black walnut. Although prized by humans for its delicious nuts and beautiful wood, the tree itself can be very dangerous to horses. Exposure to the horse is mainly through shavings used as bedding. Exposure to the tree in this manner results in laminitis or founder to varying degrees.
Originally, the tree was thought to produce a toxin in the leaves, bark, and nuts. However, more recent research suggests that only the heartwood of the tree contains the toxin responsible for causing laminitis in horses; but to be safe, horses should never be allowed direct access to these trees.
After exposure to black walnut shavings, a horse will usually begin to show the hallmark signs of laminitis within 10-12 hours. The lower legs of some horses will begin to swell, and they will be reluctant to move. Other horses might just shift their weight from one front foot to the other, or rock their weight backward. If asked to move, they will try to bear most of their weight on their heels instead of walking flatfooted. These are all classic signs of laminitis (except for the swollen legs). Other signs that might be present include a stron