Atypical Myopathy

A condition that gets a lot of attention around autumn is atypical myopathy. This is because it mainly occurs in the autumn and can have serious consequences for your horse’s health, in some cases even death. It is therefore good to know as an owner what to look out for in order to recognize and hopefully prevent this condition. 


What is it? 

Atypical myopathy is a very serious muscle condition in which the muscle cells can no longer function normally. Normally, muscle cells burn fat, which provides energy to function. But in the case of atypical myopathy, they can no longer burn fat and depend on carbohydrates as an energy source. Carbohydrates do not provide enough energy, causing the cells to have an energy deficit. Due to this energy deficit, the muscle cells die and toxins are also released during this process. 

Horses with atypical myopathy show symptoms similar to tying up. The horse will no longer move or will have difficulty moving and may even lie down. The muscles are weak and stiff and can start to twitch or spasm. The horse may start to sweat, breathing accelerates (or becomes more laboured) and the heart rate goes up. In addition, the urine may turn a reddish-brown colour, which is a sign of muscle breakdown. The horse usually does not have a fever and often eats normally. 

Although atypical myopathy is uncommon, the consequences are very serious. The symptoms are often acute and rapidly deteriorate. Horses can die from it within three days, but it could also happen within 24 hours. Unfortunately, about 70% of the cases are lethal, horses that do survive can suffer from cardiac arrhythmia or respiratory problems. 



Much research is still being done into the causes of atypical myopathy. In the United States, recent research has shown that it is caused by the absorption of the substance Hypoglycine A. It appears to occur in maple trees (seeds and leaves), but that is not always the case. If toxic maple leaves or seeds make their way onto the field, horses can eat them while grazing and this can lead to atypical myopathy. 



The best way to prevent it is to make sure there are no maple seeds and leaves in the pasture. The pasture does not have to be lined with maple trees in order for maple seeds to make their way onto the field. Because of the shape (‘helicopters’) the seeds can travel relatively long distances. Also make sure that the pasture is free of branches, mushrooms, acorns and other types of leaves. From a practical point of view, it will not always be possible to keep the pasture completely clean. Make sure that the horse has enough to eat (supplement sufficient roughage) so that you reduce the chance that the horse will look for alternative foods such as the seeds and leaves. 

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