There has been a recent surge in cases of atypical myopathy (seasonal pasture myopathy) even in areas where the disease has not previously been reported. Research carried out within the last 12 months has shown that atypical myopathy is caused by a toxin (Hypoglycin A) in the ‘helicopter’ seeds of the sycamore tree (Acer pseudoplatanus). The warm summer and early autumn has seen an abundance of seeds within sycamore trees. The recent high winds and heavy rain has resulted in large numbers of seeds falling from trees in a very short period of time posing a risk to horses grazing on surrounding fields.

If horses are grazing on pasture surrounded by sycamore trees or if large numbers of seeds blow into field’s clients can

  • Consider fencing off areas around trees
  • Removal of sycamore seeds
  • Supply extra hay especially if the pasture quality is poor; horses will not chose to eat the seeds if there is sufficient grass.
  • Reduce stocking density within pastures
  • Stable horses and turn out for short periods of time


BEVA encourage horse owners to walk around their pasture to identify any sycamore trees within or adjacent to grazing land so that they can take steps to reduce the risk of this disease. They should discuss the risks with their veterinary surgeon who will be able to advise them about measures that may be appropriate for their horses.