Do you have maple trees in or around your horse pasture?

Ingestion of wilted or dried maple tree leaves is associated with toxicities to horses.

As autumn approaches, horse owners should recognize that there may be a potential source of toxicity lingering in the pasture. Ingestion of wilted or dried maple tree (Acer species) leaves can cause toxicities to horses. Toxicity typically occurs in the autumn during normal leaf drop. However, other factors such as frost, tree trimming and storm damage may also contribute to wilted leaves.

Most reported cases indicate that toxicity is caused by red maple (Acer rubrum) leaves. However, it should be recognized that toxicosis may also occur if the leaves of other Acer species are ingested. Three other species of maple trees that are commonly found in Michigan include: sugar maple (Acer saccharum), silver maple (Acer saccharinum) and boxelder (Acer negundo).

The ingestion of wilted or dried maple tree leaves causes destruction to the red blood cells, which limits their oxygen carrying capacity. Horses may show signs of depression, be lethargic, have dark brown colored urine, increased rate of breathing and increased heart rate. Furthermore, a 1,000 lb. horse would need to ingest approximately 1.5 lbs. of leaves for toxicity to be seen. Additionally, approximately 3 lbs. of ingested wilted or dry leaves could be lethal.

It is important for horse owners to evaluate the likelihood of toxicity occurring. During a typical fall, wilted or dry leaves can be toxic for about 4 weeks. Management strategies to deal with this concern may be as simple as removing horses from the area during the fall, fencing around maple trees to minimize the exposure to fallen or damaged leaves, trimming branches out of the reach of horses, or simply cleaning up leaves and placing them in a location that is not accessible to the horse.

For more information on trees toxic to Michigan horses, please see our bulletin series in the MSU Extension Bookstore and search for Extension Bulletin: E3062.

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