Atypical myopathy – or seasonal pasture myopathy – is a severe and often fatal muscle disorder in horses, caused by eating sycamore seeds, leaves or seedlings.
Despite its name, it has become more common in recent years. It is most prevalent during autumn, when horses eat sycamore seeds that fall onto pasture, and also in spring when seedlings are germinating.
The origin of the deadly disease was unknown until fairly recently, but research in 2013/14 revealed it is caused by the toxin hypoglycin A, which is contained in certain tree seeds, including the sycamore.
The seeds are not palatable, but horses on poor quality grazing may eat large numbers.
Here’s what to look out for:
If atypical myopathy is suspected, early treatment is vital. Your vet can use specialist serum tests to support diagnosis, which are available from the Royal Veterinary College’s diagnostic laboratories.
Your horse may require admission to a specialist equine hospital for 24-hour care, where they will receive intravenous fluids and intensive care. If horses survive the first few days of treatment they usually go on to recover completely, although this can take several months.
The following steps should be taken to reduce your horse’s risk to this deadly disease:
For more information on atypical myopathy you can download a leaflet, produced by the Royal Veterinary College.