Protect horses from poisonous plants in pasture


There are countless poisonous plants in the world. Unless they are specialists who can identify all the varieties, it is often difficult for owners to roam their pastures and know what to look for.

But two of the most common plants that are poisonous to horses are white snake root and maple leaf.

“White snake root is very common in this part of the country,” said Eric Dunayer, a veterinary toxicologist at the ASPCA Animal Poison Control Center and an adjunct instructor at the University of Illinois College of Veterinary Medicine in Urbana. This plant specifically causes heart damage, an organ that can be scarred if the disease is not caught early.


Depending on the severity of the scarring, a veterinarian may declare the horse unsafe to ride. “Horses can show symptoms after eating the plant in just a few days or weeks, depending upon the amount ingested,” notes Dunayer.

Symptoms include poor coordination, weakness, muscle tremors, swelling and exercise intolerance.

Another plant poisoning in horses is red maple leaf ingestion. Fresh leaves are not a problem, but the wilting leaves are toxic, says Dunayer. If you do have a red maple in your pasture, be sure to remove fallen branches before the leaves on them start to wilt.

Clinical signs of red maple poisoning are red urine, weakness due to anemia and icterus that can be seen on the gums.

To prevent any type of plant poisoning on your farm, Dunayer recommends owners walk the pasture and send any suspicious plants to their local Extension office.


In general, many horses know not to eat certain plants, but that is not always true. For example, if you spray herbicide on the field, that in and of itself may not be toxic, but it does make many poisonous plants more palatable. This is because as the plant starts to die it becomes sweeter, and many horses enjoy that taste.

There are over 2,000 toxic plant species, but the growing patterns are very regional. For example, on the West Coast yellow star thistle is a huge problem, but not in the Midwest.

Take action

If you suspect your horse has eaten a poisonous plant, Dunayer recommends that you, call your veterinarian as soon as possible and try to identify the plant

Even if you cannot classify the plant, a veterinarian may be able to treat your horse symptomatically depending on the animal’s clinical signs. But the sooner the animal is treated, the better the prognosis.

For more information about toxic plants, contact your local veterinarian.


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