Red Maple Toxicity and Your Horse

Author: Jenifer Nadeau
Jenifer.Nadeau@uconn.edu

Reviewer: Deb Hagsrom, University of Illinois
Publication EXT183 | December 2025

DOI Pending

Introduction

Many horse owners have concerns about red maple disease in horses. Fresh red maple leaves are NOT toxic to horses, but wilted or dried leaves and the bark are extremely toxic. The scientific name for red maple is Acer rubrum. It is also known as the swamp maple, water maple or soft maple.

Fortunately, red maple disease is not that common and often easy to prevent. It’s really not necessary to just go out and cut down all of your maple trees.

Red Maple Trees Growing Conditions

Red maple trees are common in Connecticut, across the Eastern United States plus Canada, and as far West as Texas and Minnesota. They can tolerate very dry to very wet conditions. They can grow up to 100 feet tall and have an umbrella-shaped top. 

The red maple has light gray bark with reddish brown wood. The leaves are green on top and whitish underneath. The veins in their leaves are red and their leaves are jagged rather than scalloped like the sugar maple. Tiny yellowish red flowers, with five petals, appear in the spring. In the fall, the leaves will be orange, red, or yellow. All maple trees also have fruit with wings that ripen in the spring, and may fall where horses can access it.

Toxins

Fresh red maple leaves are NOT toxic to horses, but wilted or dried leaves and the bark are extremely toxic. Just over three pounds (1.5 kg) is a poisonous dose, and consumption of this amount will cause horses to become very sick. 

A known case of fatal poisoning in ponies involved consumption of 3 kg (6.6 lb) of red maple leaves over one to five days. Remember that an average 1,000 lb horse eats about 15-20 lb of forage per day. Luckily, most horses do not want to eat the dry leaves that fall, unless they are not getting enough hay or other palatable forage. 

If a horse is unable to eat forage due to bad teeth or old age, they will be at risk because they may crave forage and even eat bark to get it. Also, young horses are at greater risk because they tend to be more adventurous when eating.

Red maple contains three toxins that may negatively affect horses. Gallic acid, an oxidant, and tannins also found in oak trees, cause destruction of red blood cells, called hemolysis.

Pyrogallol, the third toxin found in the red maple, causes methemoglobinemia, which prevents red blood cells from carrying oxygen.

The combination of loss of red blood cells due to hemolysis and dysfunctional cells due to methemoglobinemia causes symptoms of weakness, depression, colic and laminitis. Horses may also develop pale gums, rapid heart rate and flared nostrils due to insufficient oxygen in the body. They may also have red-brown urine due to the red blood cells that were hemolyzed being filtered out by the kidneys. Another sign would be muddy brown mucus membranes due to the presence of methemoglobinemia.

Call a Veterinarian

If you realize your horse has eaten red maple leaves, tell your veterinarian immediately. They will likely give the horse activated charcoal, or mineral oil, to prevent the toxins from being absorbed into the horse’s blood. 

Because horses may not want to drink if they do not feel well, they will also most likely be given IV fluids to prevent dehydration. This may prevent kidney damage from the red cell remains being filtered, which will help to improve the situation. In severe cases, the horse may need a blood transfusion ,but that is reserved for when it is absolutely necessary since there in no perfect match for blood type in horses.

Preventing Maple Toxicity

Here are some ways to prevent maple toxicity in horses:

  • Provide plenty ofgood quality forage that is safe and tasty to your horse. This should help to keep the horse from eating dried or wilted maple leaves or bark;
  • After a storm, check your pasture,even if you don’t have red maples, just in case red maple debris blew onto your land. Remove any branches or leaves;
  • Inspect your hay for leaves, if you see red maple leaves, do not feed that hay to horses.

Stay vigilant after storms to help prevent this sometimes fatal disease from affecting your horse. 

Being proactive and giving your horse sufficient forage should help to prevent red maple poisoning. 

Cutting down all the red maple trees on your property is not necessarily warranted, but performing regular inspections and having a plan to manage fallen leaves in autumn will minimize the issues.

Resources

Burger, Sandra M., and the editors of Breakthrough Publications in consultation with Anthony 

  1. Knight. Horse Owner’s Field Guide to Toxic Plants. 1996. Breakthrough Publications, NY.

Burrows, George E. and Tyrl, Ronald J. Toxic Plants of North America. 2001. Iowa State University Press, IA. 

Knight, Anthony P., and Walter, Richard G. A Guide to Plant Poisoning of Animals in North America. 2001. Teton New Media, WY. 

Mazan, Melissa. The Truth About Maple Leaf Toxicity. 2022. .https://vet.tufts.edu/news- events/news/truth-about-red-maple-leaf-toxicity Accessed 8/8/24. 

A link to additional fact sheets that may be of interest is located at https://animalscience.cahnr.uconn.edu/fact-sheets/. 

The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. UConn Extension does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, UConn Extension, College of Agriculture, Health and Natural Resources is an equal opportunity program provider and employer.