Atypical myopathy caused by tree seed toxins
New research suggests that toxins from the seeds of Acer pseudoplatanus trees - commonly known as sycamores in the UK - could be the cause of equine atypical myopathy (AM) in Europe.

A highly fatal muscle disease, AM has been reported in around 20 European countries over the past 10 years, tending to occur repeatedly in autumn and spring.

Led by Dominic Votion, researchers at the University of Liege carried out the study, which involved 17 horses from Belgium, Germany and the Netherlands, all of whom were suffering from AM. The findings have been published in the June Equine Veterinary Journal (EVJ).

Experienced botanists visited the pastures of 12 of the horses, finding that the Acer pseudoplatanus was present in all, and was the only tree that each pasture had in common.

The sycamore and the box elder tree (Acer negundo) are both known to produce seeds containing hypoglycin-A, which is thought to be the likely cause of AM in Europe, as well as seasonal pasture myopathy (SPM) in North America.

Researchers identified high levels of a toxic metabolite of hypoglycin-A in the serum of all horses involved in the study.

Further research by the universities of Liege and Minnesota will attempt to determine exactly how the disease occurs. The seasonal variations of hypoglycin-A are not yet understood, though it is known that the seeds of different trees contain highly variable quantities.

Researcher Dr Jeff Gilman explained: "It is likely that the most important contributing factors to horses becoming poisoned by hypoglycin-A are the availability of seed in the field combined with lack of other feeding options.

"Without question, further analysis of the seeds and other tissues from Acer species needs to be performed along with sampling of plant materials over multiple seasons and at various stress levels."

Professor Celia Marr, editor of EVJ, added: "In immediate practical terms owners can take prompt measures to avoid exposing their horses to sycamore seeds this autumn.

"Where horses are grazing in the vicinity of sycamore trees, it is imperative that they are provided with sufficient supplementary feed as this will minimise the risk that horses might be tempted to ingest seeds containing this toxin."

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