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Check Horse Pastures for Poison PlantsBy Kentucky Equine Research Staff · September 1, 2014

Horses turned out on good-quality pasture usually won’t ingest poisonous plants as long as there are other choices. However, if pasture is overgrazed or forage is in poor condition because of drought, some horses will sample weeds or tree leaves they normally wouldn’t touch. Many of these dangerous plants have a bitter flavor that discourages horses from taking more than a small taste, but very hungry animals will sometimes be forced to graze on whatever they can find. The consequences might be colic, neurologic problems, or even death.

Horse owners and property managers should check fields for dangerous plants and trees several times a year, as not all plants will be growing in every season. Some pasture plants that pose a danger to horses are nightshade, milkweed, blue flax, poison hemlock, and buttercups. Trees and shrubs in the toxic category include black walnut, wild cherry, yew, locust, horse chestnut (buckeye), red maple, and oak.

Plants and trees may not be equally dangerous during all seasons and at all stages of growth, and some parts carry toxins while others are not a risk if ingested. For instance, wilted leaves of wild cherry and red maple trees are particularly toxic, but munching a fresh leaf or two most likely won’t hurt the horse.

Horses that are challenged by another factor may be at increased risk for plant poisoning. It is suspected that several horses in Texas were fatally poisoned when they ingested silverleaf nightshade after being dewormed with an ivermectin product. Horses that are weakened by illness or malnutrition may also be more susceptible to the effects of toxic forage.  

To protect horses in your care, follow these management steps:

  • Ask an agricultural extension agent or pasture specialist to walk your turnout area to help identify dangerous plants and tell you how to get rid of them.
  • Avoid turning horses out in pasture that is overgrazed or in poor condition.
  • Provide hay in the field if forage is not sufficient.
  • Check fields after storms and high winds to be sure tree branches have not fallen into the field.
  • Keep an eye on horses that have been turned out into a new pasture, and check with a veterinarian if they show signs of colic or neurologic problems.