As fall is quickly approaching, we often see the beauty of the autumn colors. However, that beautiful red maple tree growing in your field or barn area can be a deadly source of toxins to your horses. The following information from Cynthia Gaskill, DVM PhD, clinical veterinary toxicologist at the University of Kentucky Livestock Disease Diagnostic Center, will help you better understand the danger of this beautiful, common tree.

Red maple trees (Acer rubrum) are beautiful trees that grow extensively throughout eastern North America. Horse owners should be aware these trees can pose a serious risk to horses. Ingestion of wilted or dried maples leaves can cause damage to red blood cells and potentially death in horses (and possibly camelids, such as alpacas and llamas).

Poisoning typically occurs in late summer or fall or after storms causes tree limbs to fall within reach of horses. Other maples also have the potential to cause problems, but most documented cases are due to red maple exposure. The toxin responsible has not been identified but is apparently only found in dried or wilted maple leaves, not in fresh growing leaves.

Clinical signs in poisoned horses include depression, poor appetite, yellow or brown color to gums and membranes, dark red or brown urine, colic, and fast heart and respiratory rates. Abortion, sudden death and kidney failure may also occur. Signs typically occur within 12-48 hours of ingestion of leaves, and death can occur within days. If ingestion of dried or wilted maples leaves is witnessed, treatment can be instituted and can be effective in many cases. The mortality rate can be high and is dependent upon the dosage ingested and other factors. As little as 1.5 grams of wilted or dried leaves per kilogram of body weight can be fatal (roughly 1 pound of dried leaves in an adult horse). Post-mortem diagnosis usually is made by finding large amount of maple leaves in the stomach and intestinal contents.

Prevention is key: Do not plant maples trees near horse pastures or barns, and remove any maples that are already present; do not incorporate maple leaves into bales of hay; and remove fallen maple leaves and downed branches from pastures after storms.