QUESTION:

I've seen several articles in EQUUS over the past year regarding the fact that the wilted leaves from red maple trees (Acer rubrum) are highly toxic for horses. I interpreted 'wilted' leaves to be found if the tree lost a branch during growing season and the horses ate the leaves while they wilted. However, EQUUS has posted the warning again in their November, 2007 issue and I'm now concerned about the leaves dropping and blowing everywhere this fall.

The private barn where I board my horses has THREE red maples planted near the barn with one in particular located so close that the leaves blowing off this fall come directly into the barn and pasture. Since the trees and horses have coexisted for 10 years before my arrival with no problems, the owner is not at all interested in cutting down his lovely trees.

What experiences and guidelines can you share for dealing with this issue?

ANSWER:

Acer rubrum is the red maple tree native to the entire eastern United States. There is a toxin in the leaves (which has yet to be identified) that causes oxidative damage to red blood cells. This damage results in the red blood cells being damaged or destroyed and being removed from the cariovascular system. Disease from ingestion of the wilted leaves has a seasonal trend which causes pathology in horses from July through November. Although the leaves can be toxic when ingested in the summer, studies have shown that the leaves are more toxic after September 15. In our practice we tend to see this presentation in November.

In cases of red maple toxicity a combination of intravascular and extravascular hemolysis occurs. It will result in clinical signs such as depression, icterus, cyanosis and hemoglobinuria to name a few. If you suspect your horse is not well and may have been exposed to red maple leaves you should call your veterinarian, as this disease can result in severe anemia and death.

In regards to whether or not you should board your horse at a farm that has red maple trees, you must decide this for yourself. As these trees and horses have co-existed for may years it is difficult to expect the farm owner to cut them down. However you may need to move your horse to another property. It is always best to err on the side of caution, and enjoy the beauty of red maple trees without having to worry about your horse.