Acer Rubrum (Red Maple)

What is red maple poisoning?

The red maple tree (Acer rubrum) is a common tree in North America with bright red leaves during the fall months. Although these trees can provide great shade and foliage, they are very dangerous for horses and occasionally alpacas when the dried leaves or bark are ingested. Horses don’t normally find this a tasty snack, but when they have little or poor hay, they may be more likely to ingest the leaves or bark. Fresh leaves are often non-toxic, but dried leaves are very toxic, making this poisoning more common in the Fall when leaves drop and end up in pastures.

When horses ingest these leaves, it causes significant red blood cell damage. This can lead to poor oxygenation of tissues, as the red blood cells are not able to do their job and can severely damage the kidneys.

What might I see in my horse?

Clinical signs may develop anywhere from 12 hours to 6 days after ingestion of the bark or leaves. You may see signs of colic, weakness, depression, pale or yellow gums, incoordination, dark urine, and little to no urine production in your horse. It is important to immediately contact your veterinarian if you notice any of these signs or have a suspicion your horse may have eaten the leaves.

Along with a thorough history, your veterinarian may run bloodwork, urinalysis, or a blood smear to help with diagnosis. These diagnostics can also be used to evaluate your horse’s response to treatment.

How is it treated?

There is no true antidote for red maple poisoning, but your veterinarian can provide supportive treatments like activated charcoal, mineral oil, IV fluids, blood products, NSAIDs, and ascorbic acid (vitamin C) depending on the specific exposure and clinical signs of your horse.

Prognosis for red maple ingestion is guarded once clinical signs develop, with about 60% of cases leading to mortality. Due to this, proper prevention strategies are the best way to keep your horse safe.

How can I prevent an exposure?

  1. Ensure all horses have plenty of hay and forage.
  2. Remove or fence off any red maple trees before placing horses in the pasture.
  3. Walk pastures after large storms, especially in the fall, to remove any fallen red maple branches.




Toxicology for the Equine Practitioner Ahmad Al-Dissi, BVetSc, MSc, PhD

Veterinary Medicine, 11th; Peter Constable, Kenneth Hinchcliff, Stanley Done, Walter Grumberg, Elsevier Health Sciences, 2017.

The Truth About Red Maple Leaf Toxicity; Dr. Melissa Mazan, 2022.


Written by:

Caroline Hendron, Pet Poison Helpline DVM student extern Iowa State University Class of 2024

Samantha Koch, CVT, Veterinary Specialist II, Pet Poison Helpline