Understanding Tying Up Syndrome

Chronic Recurrent Rhabdomyolysis

This disease group causes recurring episodes of rhabdomyolysis. The severity and the intervals between episodes can vary greatly, and genetics may be an underlying factor.

To maintain their athletic capability, affected horses require careful lifelong management as well as changes in their diet and exercise regimen. Horses that are diagnosed with this condition may never be able to perform as racehorses or participate in other high-level performance events. On the other hand, they may do well in other less challenging occupations.

Polysaccharide storage myopathy (PSSM) is a common cause of chronic recurrent rhabdomyolysis in Quarter Horses, Paints and Appaloosas as well as in warmblood breeds and draft horses. PSSM is caused by a genetic defect that’s particularly common in PSSM-affected Quarter Horses and draft-related breeds. As a result, veterinarians recommend genetic testing for some breeds.

Clinical signs: Clinical indications of PSSM include repeated episodes of “tying-up” with less than strenuous exercise, muscle stiffness during and after work, exercise intolerance, and, possibly, changes in behaviour.

Diagnosis: The first step in diagnosing PSSM is ruling out other causes such as lameness through careful examination and laboratory tests. The next step is often exercise testing which may be followed up with further diagnostics like muscle biopsy and genetic testing.

Treatment: Veterinarians recommend mild exercise as soon as possible for PSSM-affected horses. Other recommendations include making dietary changes, maintaining an ideal body weight, and following a specific exercise regimen.

Dietary changes involve reducing carbohydrates and increasing fat as an energy source. While commercial diets are available, an alternative is to gradually add rice bran or vegetable oils to the horse’s feed. High-performing horses may require additional calories in their diet.

Regular exercise is important; pasture turnout is ideal and stall rest should be limited as much as possible. Unless there’s adequate preparation and conditioning, horse owners must avoid sudden changes to an affected horse’s exercise regimen — such as a long trail ride. As well, affected horses shouldn’t take long trips in a trailer or be involved in other stressful events.