Red Maple Leaf Toxicity

Is it true that the leaves of the red maple tree are poisonous to horses? If so, what are the signs? We have noticed several in our pasture now that it’s fall and are concerned.

—LL, Vermont

Dear LL,

Yes, the leaves and bark of the red maple (Acer rubrum) are toxic to horses, although the toxic principle itself is still unknown. What we do know is that horses that eat wilted or dried leaves or bark of this tree develop severe anemia due to damage to their red blood cells.

Signs of red maple poisoning include:
  • Weakness
  • Depression
  • Feed refusal
  • Abdominal discomfort (colic)
  • Laminitis
  • Pale or dark mucous membranes
  • Dark brown urine
  • Abortion in pregnant mares

Call your veterinarian immediately if you suspect your horse has eaten any part of this tree. Death can occur as quickly as 18 hours after ingestion or up to 7 – 10 days afterwards. Fluids, oxygen and blood transfusions may be helpful if administered early.

The red maple grows in the entire half of the eastern United States (and Canada), as far west as Minnesota and Texas. The best thing you can do to protect your horse from this toxic tree is to remove it from your pastures and make sure no leaves or branches fall into the pasture or are within reach of the horses. Because horses tend to nibble on potentially poisonous trees and other plants when they’re hungry, make sure your pastures are nutritious and you supplement with hay before the grass loses its nutritional value.

In researching this answer, I used two valuable resources every horse owner should have:

  1. Horse Owner’s Field Guide to Toxic Plants, by Sandra Burger and Anthony Knight from Breakthrough Publications
  2. ASPCA Animal Poison Control Center http://www.aspca.org/pet-care/poison-control/plants/?plant_toxicity=toxic-to-horses

Lydia F. Gray, DVM MA, currently serves as the Medical Director/Staff Veterinarian for SmartPak Equine. Prior to joining SmartPak, Dr. Gray served as the first-ever Director of Owner Education for the American Association of Equine Practitioners. She has authored numerous articles in publications such as The Horse, Horse Illustrated, Western Horseman and a variety of veterinary journals and magazines. Dr. Gray is also a frequent speaker at horse expos, veterinary conventions and other locations. After graduating with honors from the University of Illinois College of Veterinary Medicine and receiving her Master's Degree in Interpersonal and Organizational Communication, she practiced at the Tremont Veterinary Clinic for several years. Dr Gray is active in the American Veterinary Medical Association and Illinois State Veterinary Medical Association and enjoys training and showing her trakehner Newman in her spare time.  Find Dr. Gray on Google+

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