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