Panic Or Procrastinate? What To Do if Your Horse Has Eaten a Poisonous Plant

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 identification). Small amounts of some toxins can be fatal in a very short time while others require large amounts to be eaten over weeks or months.

Pyrrolizidine alkaloids can act in both ways, causing unthriftiness over months or blindness and staggers leading to death in just a few days. In general, however, toxicity depends on several factors: the soil, climate, and growth stage of the plant; the horse's age, weight, and individual tolerance; plus how much other feed was in the stomach when the toxin was consumed.

Some poisonous plants have specific antidotes, but for most toxic plants, the effects can only be treated symptomatically. This means supportive care and measures to limit further exposure until the crisis has passed. Depending on the specific toxin (even if the horse survives), there can be permanent signs of disease. For example, horses which have eaten enough locoweed over time to show central nervous system signs, such as incoordination, might never be safe to ride. Locoweed also is an example of a poisonous plant that horses might seek out to eat once they have had some because it could be addictive.

Since there are many different kinds of poisonous plants, there are many different signs of poisoning. The most common signs of toxin ingestion include the following: difficulty swallowing or breathing, colic, founder, hyperexcitability/seizures/incoordination, limb edema or photosensitivity, and even collapse and sudden death. Often these syndromes must be differentiated from similar diseases caused by infectious, nutritional, or age-induced problems by a thorough case history, physical examination, and diagnostic workup. Owners should not attempt to treat poisoning themselves but should contact their veterinarian immediately, which could mean the difference between life and death.


Rather than treat a horse which already has begun to show signs of eating a poisonous plant, owners should strive to prevent their horses from ingesting the plants in the first place. Know the common poisonous plants in your region of the country, including the time of year they are the most palatable or the most toxic. For example, white snakeroot poisoning usually only occurs during midsummer to early winter when the pasture has become eaten down or dried up. Limiting pasture time during those parts of the year and making sure the horse is well fed before being turned out reduce but do not eliminate the risk. Also, do not overstock pastures with too many horses per acre, and maintain pastures accordingly.

Provide the best quality hay and grain possible, checking each flake of hay and scoop of grain carefully before feeding it. Hay should be green and smell pleasant. Grain should not have any corn fines or screenings, since these often contain the compound that causes equine leukoencephalomalacia, commonly known as moldy corn poisoning. If you have any doubts about the quality of your feed, ask your veterinarian to send in random samples for testing; even corn that looks fine can be fatal. You could even organize a "pasture walk" for your local riding club led by an expert who can point out poisonous plants.


It's a good idea to know to whom you should turn before you find yourself in an emergency situation. For poisonous plant identification, start with your local veterinarian, who can put you in touch with your county extension agent and the nearest university. Greenhouses, herbariums, florists, and botanists can be other sources of expert information. Weed experts usually need the entire plant (including the roots) in order to identify it. For immediate identification, wrapping the plant in moist paper will suffice. However, if the plant needs to be mailed somewhere, pressing it dry between papers is best.

About the Author

American Association of Equine Practitioners

AAEP Mission: To improve the health and welfare of the horse, to further the professional development of its members, and to provide resources and leadership for the benefit of the equine industry. More information:

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