Should I be worried about atypical myopathy?

XL vet, Kirstie Pickles, explains what you need to know about atypical myopathy. 


What is atypical myopathy?

Typical myopathy is a frequently fatal muscle disorder seen in a grazing horses in the autumn and/or spring.

Recent research has indicated that ingestion of a toxin (hypoglycin A) from the seeds of the sycamore tree is the likely cause.

Previously rare in the UK, the number of reported cases has increased substantially in recent years (from only three in 2010 to 165 in 2016). Although part of the increase may be down to better awareness and recognition, it also appears to be coming more frequent. 

What are the symptoms? 

Clinical signs usually appear suddenly, are severe and progress rapidly. Early signs consist of:

  • Tiredness
  • Decreased appetite
  • Colic
  • Muscle stiffness or lameness 

Affected horses pass dark-coloured urine die to an increased myoglobin content (this is a breakdown product of muscle). 

Which horses does it affect? 

Horses that develop atypical myopathy are usually kept in sparse pastures with an accumulation of dead leaves, dead wood and trees in or around the pasture and are often not fed any supplementary hay or feed.

How can I prevent atypical myopathy? 

Preventative measures consist of:

  • Restricting pasture access to young horses when outbreaks occur
  • Providing additional concentrates in spring and autumn or of pasture is poor, a salt block
  • Permanent stabling during critical periods (i.e. autumn and spring)
  • Reducing the time spent at pasture during critical periods