Sycamore Maple Seed Toxicity in Horses Studied

Equine atypical myopathy (EAM), an often fatal disorder found in grazing horses predominantly in autumn, could be linked to sycamore maple seed ingestion, according to the results of a study conducted by a German research team.

When ingested, hypoglyclin A (HGA), a toxin found in the seeds of sycamore maple trees (Acer pseudoplatanus), can cause EAM, characterized by weakness, progressive muscle stiffness and damage, recumbency, and death. There is currently no specific treatment available. Equine atypical myopathy, along with a very similar condition referred to as seasonal pasture myopathy, has been observed in nearly all European countries, the United States, and New Zealand.

This case report involved a 2 ½-year-old draft mare that developed clinical signs of EAM 36 hours after being moved onto a pasture containing sycamore maple trees; the horse died 12 hours after the onset of clinical signs. Examination of tissue, blood, and urine samples, in addition to the presence of sycamore maple tree seed fragments in the stomach and evidence of severe muscular myopathy, led researchers to conclude there is a plausible link between EAM and the consumption of sycamore maple seeds containing HGA.

“Our study shows that hypoglycin A intoxication associated with ingestion of sycamore maple tree seeds is a threat to horses … in Europe,” said Robert Klopfleisch, DVM, Dipl ACVP. “When we discussed the case with practitioners, we experienced a lack of awareness that maple trees on horse pastures are a deadly threat for the animals.

“In addition, we show how hypoglycin A is detectable in urine and blood of affected animals, which is important for clinicians and pathologists,” he added.

In the meantime, Klopfleisch urged owners to check their pastures: “Horses may not have ingested maple tree seeds yet, but under specific circumstances they might, and this has dramatic consequences.”

He also suggested additional research could further veterinarians’ and researchers’ understanding of the disease and how to manage it. “I think we need more studies on how to recognize the intoxication early and how to treat it properly.”

This study, “Equine atypical myopathy caused by hypoglycin A intoxication associated with ingestion of sycamore maple tree seeds,” was published in Equine Veterinary Journal

About the Author

Natalie DeFee Mendik, MA

Freelance journalist Natalie DeFee Mendik is a multiple American Horse Publications editorial and graphics awards winner specializing in equestrian media. She holds an MA in English from Colorado State University and an International Federation of Journalists' International press card, and is a member of the International Alliance of Equestrian Journalists. With over three decades of horse experience, Natalie’s main equine interests are dressage and vaulting. Having lived and ridden in England, Switzerland, and various parts of the United States, Natalie currently resides in Colorado with her husband and two girls.

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