Veterinarians from New Bolton Center advise horse owners to be on the lookout for toxic, wilting leaves

[October 20, 2010; Kennett Square, PA] – That pretty maple tree in your pasture turning a vibrant shade of vermillion could be a murderer in disguise. The native red maple (Acer rubrum) is found throughout the northeast. Though harmless most of the year, in autumn the wilted and dried leaves of the red maple can be highly toxic to horses if ingested.

“When the leaves are eaten by the pony or horse, the unidentified toxin within destroys red blood cells,” explains Lisa A. Murphy VMD and Assistant Professor of Toxicology at University of Pennsylvania School of Veterinary Medicine’s New Bolton Center. “Hemolytic anemia is the result, and the condition can be fatal.” It doesn’t take many leaves to cause the illness, little more than a pound for a 1000 pound horse, and a horse with poor grazing options may easily ingest enough to die. The illness is fatal in about two-thirds of cases, causing death within a week.

A horse with red maple leaf poisoning will seem lethargic, easily fatigued and possibly short of breath, according to Raymond W. Sweeney VMD and Chief of the Section of Medicine at New Bolton Center. The destruction of red blood cells will cause the urine to be visibly colored red or brown. Gums and the white of the eyes will be yellowish, and the horse may have a fever. Veterinary examination will further reveal a severe decrease in the concentration of red blood cells. “Pregnant mares may abort even in the absence of anemia,” adds Dr. Murphy.

“Like many diseases, prevention is paramount, and owners should take steps now to avoid exposure of their horses to red maple leaves,” says Dr. Sweeney. “However, if a horse is seen to consume wilted leaves, or begins to show signs of toxicity such as red urine, immediate veterinary attention should be sought.”

Early diagnosis followed up with immediate supportive therapy can save the horse’s life, says Dr. Sweeney. Treatment typically includes administration of activated charcoal, via stomach tube, to absorb any remaining toxins in the gastrointestinal tract, followed by intensive supportive therapy including intravenous fluids, and possibly blood transfusions. It is very important to keep the horse confined and quiet until his red blood cell volume is back to normal.

Examine pastures for the red maple leaf, distinguishable by the serrated edges of the leaf, and silvery underside. The red maple has green leaves, which turn brilliant red in the fall, and red stems. Make certain not to toss any leafy branches from the tree or rake any fallen leaves into pastures or other areas accessible by horses. Watch out for neighbors’ branches that may fall into your fields, particularly after storms. The safest course of action is to remove all red maple trees from the vicinity of horse pastures.