The More You Know: Protect Your Horse From Poisonous Plants

March was National Poison Prevention Awareness Month — make sure you know how to protect your horses from poisonous plants and recognize signs of toxicity. 

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Oklahoma State University professor, Extension equine specialist Dr. Kris Hiney details poisonous plants impacting horses, and shares this harrowing first-hand account with Valley Vet Supply.

The pastures were recently cleared from overgrown trees and brush, and Kris Hiney, PhD, Oklahoma State University assistant professor and Extension equine specialist, closely looked over the brush piles to make sure no poisonous plants or trees had surfaced. “All clear,” she thought as she let her two horses back into the field.

“The very next day, they were already showing toxicity symptoms,” Dr. Hiney said. “It turns out I did have black locust trees in the pasture, and when the horses had a chance to get to them, it almost killed them.”

Of the two horses, one had lower tolerance to the toxic tree. His heart rate was elevated over 90 for a full 24 hours and to save his life, he required three days of supportive care in the veterinary clinic. Luckily, both horses survived.

Horse owners need to be familiar with poisonous plants and signs of toxicity. There are many poisonous grasses, plants and trees that can gravely impact horse health, such as black locust trees, Johnsongrass, white clover, maple trees, locoweed, tansy ragwort and black walnut trees. Fescue grass can be toxic to broodmares and their foals, causing thickened placentas and even abortions.

This University of Minnesota poster shows pictures of poisonous plants and ways to better understand signs of toxicity:

Below are common symptoms of toxicity in horses:

  • Change in behavior
  • Anxiety
  • Depression
  • Neurologic issues
  • Seizure
  • Abnormal gait
  • Tremors
  • Stocking up or founder
  • Elevated heart rate
  • Brown or discolored urine
  • Mouth blisters
  • Colic

If horse owners fear their horse might have ingested a poisonous plant, “Call a veterinarian immediately,” Dr. Hiney said. “If horses do not receive the right care, toxicity can be a big deal. Death is often a real possibility.”

As the weather affects forage available to horses in turnout situations (especially with summer drought or winter conditions), horses are more inclined to ingest unfamiliar plants or leaves. To help prevent plant toxicity, make sure horses have adequate rations of quality hay or grass in front of them. Dr. Hiney encourages horse owners to work closely with their county extension agent to identify potentially harmful grasses, plants or trees that may surface in their pastures. Horse owners can also invest in a spray system to eliminate unwanted plants and weeds.

“Anytime there is something novel in their pasture, horses are going to investigate it,” Dr. Hiney warned. “I thought everything in my pasture was safe, but it turns out I was wrong. Be very careful, and take a look at what is accessible to the horses.”

About Valley Vet Supply
Valley Vet Supply was founded in 1985 by veterinarians to provide customers with the very best animal health solutions. Building on over half a century of experience in veterinary medicine, Valley Vet Supply serves equine, pet and livestock owners with thousands of products and medications hand-selected by Valley Vet Supply founding veterinarians and their professional staff. With an in-house pharmacy that is licensed in all 50 states, and verified through the National Association of Boards of Pharmacy (NABP), Valley Vet Supply is the dedicated source for all things horse, livestock and pet. For more information, please visit