Maple tree menace
The danger posed by wilted or dried red maple leaves has long been known, but evidence is growing that, under the right circumstances, other types of maple leaves can poison horses as well.
Maple trees are commonly used for landscaping in many areas of North America and especially in the northeastern states. Some species such as the sugar maple are economically valuable for the production of maple syrup, and wood from the trees is used for the manufacture of furniture and musical instruments. However, some maple species have a sinister side---horses and ponies as well as donkeys, mules and zebras eating the fallen, wilted or dried leaves can be fatally poisoned.
Although the dangers of poisoning from one species, the red maple ( Acer rubrum, also called swamp maple or soft maple), are well known, research suggests that other trees of the species, including the sugar and silver maples and their hybrids, may also pose a threat. In fact, cases of maple poisoning have been identified in horses that consumed wilted leaves from the sugar maple (Acer saccharum).
Horses are most likely to encounter wilted leaves after summer storms bring down branches or blow leaves into pastures and paddocks. In the autumn, fallen maple leaves are generally less palatable to horses, but they also pose a serious threat when they are consumed. Fresh, green leaves of any maple species are less dangerous but may still contain some level of toxins. The bark and twigs of maple trees may also be toxic if consumed by horses.
“Red maple toxicity is not common, simply because most people feed their horses well and pay attention to what their horses are eating,” says Anthony Knight, BVSc, MS, DACVIM, a large animal veterinarian, plant toxicologist and professor emeritus at Colorado State University. “A horse may eat a few maple leaves on occasion, but an adult horse would need to eat one to two pounds of the dried or wilted maple leaves to be affected by the toxin. It is the dose that makes the poison.”
Still, to keep your horse safe, it’s a good idea to be able to identify the maple species---sugar and silver as well as red maples---because they are common in or around pastures and may be encountered on the trail.