50. Red Maple
TOXICITY RATING: High, death is common.
ANIMALS AFFECTED: Horses only.
DANGEROUS PARTS OF PLANT: Leaves, especially when fallen, damaged, or wilted.
CLASS OF SYMPTOMS: Breathing difficulties, jaundice, dark brown urine, death.
PLANT DESCRIPTION: Red maple is a tree of medium size, occurring naturally or planted as an ornamental. Young bark is a smooth gray color, older bark is dark and broken. Leaves are 3 to 5 lobed, with shallow notches between lobes. Underside of leaves are white. Leaves are green during the growing season and turn red in the fall. Buds, twigs, flowers, and petioles are red. The sap is not milky.
SIGNS: The toxin has not been identified, but is believed to be an oxidant due to its effects on red blood cells. Only horses are known to be affected. The ingestion of wilted or fallen leaves causes massive destruction of red blood cells, and the blood can no longer carry sufficient oxygen. Ingestion of 1.5 pounds of leaves is toxic, and ingestion of 3 pounds is lethal. Wilted or dry leaves remain toxic for about a month. Fresh and undamaged leaves have not been implicated, but ingestion is still not advised. Clinical signs develop within one or two days and can include depression, lethargy, increased rate and depth of breathing, increased heart rate, jaundice, dark brown urine, coma, and death. Approximately 50% to 75% of affected horses die or are euthanized.
FIRST AID: The first step is to prevent further consumption by the horse (and any other horses on the same pasture). There is no specific treatment, and contacting a veterinarian is advised. The veterinarian may use methylene blue, but this is not often effective in horses, but can be tried early in the course of the disorder. Treatment is symptomatic and supportive and can include mineral oil and activated charcoal to prevent further absorption in the stomach, oxygen, fluid support, and blood transfusions.
SAFETY IN PREPARED FEEDS: Reports are lacking, but red maple should not be considered safe in hay, especially if it is freshly baled.
PREVENTION: Do not allow horses access to red maple. Most poisoning
occur in the late summer and fall when leaves fall into pastures,
or at any time when fallen limbs are placed in pastures. Apparently
the leaves are palatable, thus increasing the risk of toxicosis.
Do not incorporate red maple leaves into hay bales.