It is a common misbelief that horses always instinctively know which plants, bushes or trees are poisonous for them. Reality is, that horses will generally avoid poisonous plants, unless forage is scarce. Especially during winter and early spring, when other forage species are limited, horses could be more prone to consuming whatever plants they find in their field. There is also always a chance of poisonous plants being accidently consumed. Depending on the plant toxin, consumption can cause a wide range of symptoms from nervousness, muscle weakness, incoordination and salivation to irritation and colic. The most common acute toxins can kill a horse within just a few hours, which makes it close to impossible to notices warning signs of intoxication before it is too late.

Barn managers and horse owners should be aware of the most common poisonous plants for horses in their area. Eliminating them is a critical part of proper pasture management and will help keeping your horses safe.

• Yew shrubs – The needles and seeds of this common ornamental shrub are extremely toxic for horses and should never be located on horse farms. Horses that have consumed yew will die within 1-3 hours.
• Oleander – These landscaping shrubs are very common in the Southern United States. Already fairly small quantities can be lethal or cause a painful colic. If you encounter them on a trail ride or other farms, keep a safe distance with your horse.
• Poison hemlock – This naturalized herb is most commonly seen along roadways or swampy areas but has expanded into pasture lands within the last few years, according to the University of Kentucky, College. The toxic alkaloid content of the plant varies but can be deadly for horse within hours. Areas where poison hemlock is growing should be fenced off for horses.
• Wild cherry trees – Are toxic to horses. The seeds, foliage, and bark produce hydrogen cyanide, a deadly compound. Wilted leaves are even more toxic than fresh ones.
• Red Maple leaves - Poisoning is associated with horses eating wilted red-maple leaves from broken branches or when horses reach over fences. Similar to wild cherry, the Red Maple leaves are sweeter and therefore more palatable for horses when they are wilted.

In addition to preventing plant poisoning by pasture management, it is vital to supply sufficient forage for your horses. If good quality forage is plentiful in the pasture, horses will avoid most poisonous plants. Learning about your regional plants that are poisonous to horses or asking your vet about them will help keeping your horses safe.

References:

Ontario Ministry of Agriculture, Food and Rural Affairs Rapid and Unexpected Death in Horses Part A - Toxins (gov.on.ca)

Rutgers New Jersey Agricultural Experiment Station FS938: Poisonous Weeds in Horse Pastures (Rutgers NJAES)

Michelle Arnold, DVM and J.D. Green, MS, PhD Poison Hemlock: Toxic to Horses and Other Animals – The Horse

Lindsay Day, REMT 10 Plants and Chemicals That Are Toxic to Horses – The Horse

Tanja Schnuderl is a team member with The Equine Expert LLC, a multi-discipline equine expert witness and consulting firm with expert equestrians offering legal expert witness and consulting services in court cases and legal matters. Tanja is an expert on Barn Management and Horse Behavior. She is the Barn Manager for Moon Rising Farm just outside Washington DC and Principal of Sigma Equine LLC, an equine appraisal business. Tanja grew up in Germany and was a paralegal for many years. For more information on Tanja Schnuderl email info@theequineexpert.com, www.theequineexpert.com