Lethal Red Maples
—Larissa, via e-mail
A: I’m so sorry to hear about your recent loss. How maple leaves affect horses isn’t entirely clear to us. We know that wilted leaves (which can come from downed tree limbs or occur, as you discovered, after a frost) are dangerous, and most poisoning cases occur in the autumn. We also know that it doesn’t take much to poison a horse—less than a pound of dry leaves could be fatal for a pony.
Based on some work that a student did in my laboratory, we know that red maple leaves contain gallic acid. Intestinal bacteria can convert gallic acid from leaves into pyrogallol, which can damage red blood cells and, we believe, could be responsible for the clinical picture of maple poisoning (signs appear within 12-24 hours and include depression, poor appetite, yellow or brown gums and membranes, dark red or brown urine, colic, and fast heart and respiratory rates; abortion, sudden death, and kidney failure might also occur). If this is true, then individual horse factors are important as well: The horse would have to have the right intestinal bacteria to produce the toxic pyrogallol from the leaves. Our work thus far has been done predominantly in test tubes, and we still need blood samples from accidentally poisoned horses to verify that our hypotheses are
Create a free account with TheHorse.com to view this content.
Stay on top of the most recent Horse Health news with