Most of the year your horse can happily munch on a few fresh red maple leaves straight off the tree with little to no worries. The maple leaves that fall normally in October and November appear to be safe. But eating fresh wilted maple leaves ? such as occur post bad storms like Hurricane Irene when trees fall into pastures ? is another situation altogether.
Over the summer, the red maple leaves build up levels of a toxin called gallic acid. Wilted leaves have the most available toxin and can remain toxic for a few weeks. For the average-size horse, 0.7 to 1.5 kg of wilted leaves can lead to poisoning and hemolytic disease.
The gallic acid acts on the red blood cells to cause breakdown and a potentially fatal anemia. Many horses die within 18 to 24 hours of eating the wilted leaves. Horses who survive beyond that will be depressed, have discolored mucous membranes and pass dark colored urine. Some horses may develop colic or laminitis. Approximately 60% of all horses will die.
Never put pruned tree branches into the pasture. After any storm, check your pastures for trees that have fallen down and remove them. Red maples need to be removed as soon as possible, especially from mid to late summer and early fall.