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Managing Equine Polysaccharide Storage Myopathy

"Tying up" is a term that most horse owners are familiar with. It is often known as "Azoturia" or Monday morning disease. Affected horses have painful muscles and are stiff, often reluctant to walk and may sweat more or have an increased respiratory rate.

Tying up is technically termed Equine Exertional Rhabdomyolysis (ER), which is a fancy way of saying “horse muscle cells breaking down after working”- disease!

Recurrent Equine Rhabdomyolysis

Recurrent Equine Rhabdomyolysis (RER) is common in racing thoroughbreds and occurs more often in younger horses and in fillies. This disease process is caused by a problem regulating calcium in the horse’s cells. In simplest terms, calcium is like a good post office system, it is required for messages to get around the animals body. Genetics and diet are considered to be the main contributing factors to this form of tying up.

Many horses that suffer from recurrent exertional rhabdomyolysis benefit greatly from changing diet to Horse Care 10 or Horse Care 14, depending on their work level. This is discussed in our article All Tied Up.

However, there are other types or causes of “tying up” type diseases.

Equine Polysaccharide Storage Myopathy: (EPSSM)

This is a type of tying up mostly associated with Quarter horses and the draught type breeds. The exact process of the disease is still being researched but it is believed that it is caused by a problem in how the horse metabolises or breaks down carbohydrates. It tends to appear more in mature horses (about eight years old) and so should be considered if your hunter is showing signs of stiffness during the coming season. It can also show in a milder form, showing reluctance to exercise properly, shortened stride, poor performance, generalised low grade stiffness, back pain and even repeated episodes of mild colic.

Definitive diagnosis of EPSSM requires taking a muscle biopsy and having it tested at a suitable laboratory. A suspected diagnosis can be made by your vet on the basis of the clinical signs and increases in the muscle enzyme markers in blood. There is no once off cure for EPSSM but changes to exercise and diet can lead to it being very well managed.

Diet change to one that is high in fat and fiber and low in starch and sugar is the mainstay of long-term therapy of EPSSM.  Exercise, even if it is just turnout, is the other important part of therapy.

All horses should be fed an adequate amount of good-quality forage. Horse Care 10 and Horse Care 14 have low starch content and are full of super fibres. While a lack of vitamin E and selenium in the diet will not directly cause EPSSM, they are very important antioxidants that are of huge benefit in managing the disease. Both Horse Care 10 and 14 have high levels of vitamin E and selenium. Levels of fat (or oil) in the diet can be topped up using products such as Kentucky Karron Oil from Foran Equine. Kentucky Karron Oil is emulsified so that it can be more quickly and completely absorbed in the horse’s digestive system.

Be warned it may take some months to see the effects of the new management system. This is because the horse’s digestive cells and muscle cells have to readjust how they process energy sources.

Some studies have shown up to a 66% incidence of EPSSM in horses, many of these cases were discovered post mortem and had not been noticed by the owners or vets. Perhaps many cases of stiff or “lazy” horses are in fact suffering from EPSSM and could be superstars in their fields on the appropriate diet!

EPSSM is recognised as a “new” disease but in fact tying up has been described for decades and we are just learning that there are many causes of the symptoms of tying up. It is only now that we are better able to understand and differentiate between those causes. Regardless of the pathway of disease all horses susceptible to tying up and muscle problems in general will benefit from low starch diets such as Horse Care 10 and Horse Care 14.

Please remember:

  • Acute episodes where horses are in respiratory distress and unable to walk should be considered a veterinary emergency.
  • If you are changing your horses feed DO IT SLOWLY. Sudden changes cause problems.

If you wish to discuss EPSSM, Horse Care 10 or Horse Care 14, or for any other queries related to caring for your animals please contact our nutrition team who will be happy to help.

  • Tags:
  • Horses
  • Managing Equine Polysaccharide Storage Myopathy
  • Painful Muscles
  • Stiff Muscles
  • Tying Up