By Tom Guthrie
As the autumn season progresses and trees lose their leaves, some pastures may have a significant amount of leaf coverage. Horse owners and/or caretakers should be aware of what types of trees are in or around their horse pasture(s). Consumption of wilted or dried red maple tree (Acer rubrum) leaves can be toxic to horses because they can cause destruction to the red blood cells, which limits their oxygen carrying capacity.
Toxicity typically occurs in the fall during normal leaf drop and when pastures tend to have less available forage. However, other factors such as frost, tree trimming and storm damage may also contribute to wilted leaves.
While most reported horse toxicity cases implicate red maple (Acer rubrum) leaves, consumption of other Acer specie leaves by a horse is not advised. Other species of maple trees that are commonly found in Michigan include: sugar maple (Acer saccharum), silver maple (Acer saccharinum), norway maple (Acer platanoides) and boxelder (Acer negundo).
Signs of toxicity
- Depression
- Lethargic
- Dark reddish to brown colored urine
- Increased rate of breathing and increased heart rate
Notables
- Fresh leaves typically are not an issue but consumption is still not advised
- 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. Small equine like ponies and donkeys can show toxicity symptoms after ingesting as little as 0.5 lbs. of maple leaves.
- Wilted or dry leaves can remain toxic for about 4 weeks
1.5 pounds of red maple leaves
Management considerations
Michigan State University Extension recommends that horse owners/caretakers carefully evaluate the likelihood of toxicity from maple leaves occurring. Strategies to avoid consumption and/or horse exposure to toxic leaves include:
- Manage pastures(pdf) to ensure there is enough available forage throughout the grazing season.
- Ensure horses have an alternative forage source (hay) during the fall when turned out to pasture.
- Temporarily fence around maple trees to minimize the exposure to fallen, damaged leaves or wilted leaves.
- Trim lower branches so they are out of the reach of horses.
- Remove horses from the pasture or turnout area during the fall.
- Clean-up leaves and place them in a location that is not accessible to the horse.
- Removing the tree(s) – this may not be practical in some cases. Leaves may drop or blow into the pasture from outside the fence. In addition, these trees may be the only source of shade in the pasture, which may make removing the tree(s) impractical.
- Don’t plant trees that may be a risk factor in or close to horse pastures.