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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

Lydia F. Gray, DVM, MA SmartPak Staff Veterinarian and Medical Director Dr. Lydia Gray has earned a Bachelor of Science in agriculture, a Doctor of Veterinary Medicine (DVM), and a Master of Arts focusing on interpersonal and organizational communication. After “retiring” from private practice, she put her experience and education to work as the American Association of Equine Practitioner’s first-ever Director of Owner Education. Dr. Gray continues to provide health and nutrition information to horse owners through her position at SmartPak, through publication in more than a dozen general and trade publications, and through presentations around the country. She is the very proud owner of a Trakehner named Newman that she actively competes with in dressage and combined driving. In addition to memberships in the USDF and USEF, Dr. Gray is also a member of the Illinois Dressage and Combined Training Association (IDCTA). She is a USDF “L” Program Graduate and is currently working on her Bronze Medal. Find Dr. Gray on Google+

Posted in Barn Skills, Misc. Topics, Seasonal Horse Care

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5 comments on “Red Maple Leaf Toxicity
  1. connie scott says:

    My horses ate a few red maple leaves from the tree.
    Do I have to be worried?
    They act alright and eat alright.
    I’m scared.
    Connie Scott

    • SmartPak SmartPak says:

      Hi Connie, we can certainly understand your concern. We recommend that you have your veterinarian check on your horses as soon as possible, since early treatment is critical in cases of maple poisoning. – SmartPaker Kerri

  2. isobel h says:

    hi , my horse ate a very wilted dry crispy red maple leaf , only 1 but should i be worried . thanx

    • SmartPak SmartPak says:

      It takes about 1.5 to 3 lbs of wilted maple leaves to cause toxicity in a 1,000lb horse (that’s 0.7 to 1.5kg of leaves per 450kg horse) so one leaf shouldn’t cause a problem. However, because serious clinical signs can occur within 1 to 2 days and you may not be absolutely, positively sure that your horse only ate one leaf, I recommend contacting your veterinarian right away for his or her advice.
      Dr. Lydia Gray

  3. isobel h says:

    he is not showing any sighnes

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