You provide plenty of good quality feed, water, and turnout–do you still have to worry about your horse’s getting sick from eating a poisonous plant? While common sense and good horse management are your horse’s best protection, toxicology, like most other life sciences, has many unanswered questions. But by taking advantage of what is known, you can decrease the chance of your horse eating the wrong plant at the wrong time.
Since most poisonous plants do not taste very good, often horses will need a reason to eat them. The most common reason is simply hunger–the horse isn’t getting enough to eat or the nutritional quality of the diet is poor. Owners also can unintentionally feed toxins to their horses through contaminated hay and grain or by offering certain tree and bush clippings. Just a few leaves from the Japanese yew, a common lawn ornamental, can kill a horse within hours. Leaves from maple trees also can be fatal.
Allowing horses to graze a pasture after it has been sprayed with a herbicide, but before the weeds have died and disappeared, is another commonly overlooked reason a horse might become poisoned. Phenoxy compounds such as 2,4 D are believed to make the plants taste better and, in some cases, to increase concentrations of natural plant toxins.
The first thing to do if you suspect your horse has ingested a poisonous plant is to prevent further exposure. Depending on the source, this might mean removing your horse from the pasture and putting it into a stall or removing all hay, grain, and bedding from an already stalled horse. Contact your veterinarian immediately. While waiting, attempt to determine how much was eaten and what was eaten (see the References section at the end of this article for tips on plant identificatio