As autumn edges closer now is the time to identify sycamore trees in or around horse pastures, veterinarians from the British Equine Veterinary Association (BEVA) say.

Sycamore seeds are toxic and can cause the fatal disease often called atypical myopathy (AM) or, more correctly termed, seasonal pasture myopathy (SPM). While trees are in full leaf and the seeds clearly visible at this time of year, it is easier to identify them and take steps to minimize horses’ risk of contracting the disease.

A highly fatal muscle disease in horses, SPM’s origin was, until recently, unknown. Research carried out in in 2013 and 2014, however, revealed that the condition is caused by the toxin hypoglycin A, which is contained in some tree seeds—including those of the sycamore.

High winds during last autumn resulted in considerable pasture contamination with sycamore seeds and saw veterinary practices across the United Kingdom managing large numbers of horses with this condition. Data from the National Equine Health Survey showed a four-fold increase in cases last year.

Horses that develop SPM are usually kept in sparse pastures containing an accumulation of dead leaves, wood, and trees, and these animals often are not fed any supplementary hay or feed. While the seeds might not be directly palatable, horses grazing on poor quality pasture could ingest considerable numbers of them accidentally.

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Horse owners are advised to identify sycamore trees on or near grazing land and take steps to prevent the seeds falling where they are in reach of horses, including:

  • Restrict access