Red Maple Toxicosis

Here in New England, we take our beautiful maple trees for granted. They provide us with our famous maple syrup in the spring, and they turn a fiery red in the fall which pleases the eye and draws tourists by the droves to boost our economy. Because of their beauty, many people use them in landscaping around their houses, or preserve existing trees when building a new structure like a barn. What many people don’t realize is that these beauties can be deadly for equines.
The Red Maple (Acer rubrum) is the tree most commonly associated with Red Maple Toxicosis in horses. It is native to the north east, and is a deciduous tree (it loses its leaves in the winter). The primary danger comes in the fall, when the leaves are wilted, but the leaves are dangerous any time they have been knocked off the tree. Storms will frequently cause a spike in Red Maple Toxicosis as they knock branches into pastures and curious horses eat the wilted leaves. Research suggests that leaves build up a higher level of the toxic compounds as the summer progresses, so fall leaves are more toxic than spring leaves.

Red Maple Toxicosis causes damage to a horse’s red blood cells (RBC), which can lead to death. Scientists aren’t exactly sure what causes the damage, but there are 3 compounds that they suspect are the culprits. These compounds change the RBC so they can’t carry oxygen anymore. For a 1000lb horse, ingestion of as little as 2 pounds of leaves can cause toxicosis.
Clinical signs typically occur within a few hours, and death can occur in as little as 18-24 hours. Initial signs noted are typically colic or fever. Depression, blue or purple gums, and dark red-brown urine are common signs noted if a horse survives the first 24 hours. Horses become anemic, which is relatively easy for your vet to discover with simple blood tests. More than half of horses affected will die.

Now, you might be concerned about how to identify which maples are toxic. Researchers aren’t certain that only the Red Maple causes problems, as the toxic compounds have been found in the Silver and Sugar Maples as well, although there haven’t been any confirmed cases of poisoning related to these species. If concerned, an owner can simply prevent access to any sort of maple tree. To identify a Red Maple, look at the leaves. The leaf margins are serrated and the margins of the center lobe are close to parallel with the central vein. The Sugar Maple (Acer saccharum), which is extremely common in New England, has smooth leaf margins. The Silver Maple (Acer saccharinum) has heavily indented leaf lobes and the margins are serrated.

If you suspect that your horse has consumed Red Maple leaves, call your vet immediately. Due to the serious nature of the poisoning, intense supportive care is usually necessary. Blood transfusions, IV fluids, and constant pain medications are all the golden standard of treating these cases, which typically require hospitalization in a referral facility. Don’t delay calling your primary veterinarian out, as this could save your horse’s life!
Eleanor Warner, DVM