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Recurrent Exertional Rhabdomyolysis

What Is It?

  • Recurrent Exertional Rhabdomyolysis (RER) or “tying up” is seen in many breeds of horses including American Quarter, American Paint Horses, Appaloosas, Thoroughbreds, Arabians, Standardbreds and Morgans.

  • A wide variety of causes for RER have been proposed including electrolyte imbalances, hormonal imbalances, lactic acidosis, and vitamin E and selenium deficiencies. The genetic component is under investigation.

  • However most recently, some specific causes of RER have been identified in the horse. These include a disorder of muscle contractility or excitation contraction-coupling (chronic intermittent rhabdomyolysis) and a disorder in carbohydrate storage and utilization (polysaccharide storage myopathy).

  • A number of horses, predominantly fillies, will have recurrent episodes of rhabdomyolysis even with light exercise.

  • The most common form of tying-up may be sporadic tying-up, which occurs when exercise exceeds a horse’s level of fitness. This is typically seen where horses are not regularly exercised and then are overworked.

Dietary and Management Recommendations

  • High fat and fiber rations along with good quality grass or grass-legume mix are most suitable for this disorder. Strict control of hydrolyzable carbohydrate is of the utmost importance.

  • The diet should be adjusted to include a balanced vitamin and mineral supplement. Dietary fat supplements may help to maintain bodyweight without providing excessive soluble carbohydrates.

  • Daily exercise is essential, whether in the form of turnout, lunging or riding.

  • Stall rest is not recommended following an episode of tying up. Complete stall rest is counterproductive and increases the likelihood that the horse will develop RER when put back into training. The initial muscle pain usually subsides within 24 hours of acute RER and daily turnout in a small paddock can be provided at this time. Subsequently, a gradual return to performance is recommended once serum cytokinase is within normal range.

  • Prevention of further episodes of RER in susceptible horses should include standardized daily routines and an environment that minimizes stress.

  • Electrolyte supplementation may be warranted in very hot and humid weather for horses in intensive training.

  • Always provide free-choice salt and fresh, clean water.


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