Recurrent exertional rhabdomyolysis

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Recurrent Exertional Rhabdomyolysis

Chronic Exertional Rhabdomyolysis

Recurrent Exertional Rhabdomyolysis (RER) is one of the most common muscle disorders in horses, affecting over 10% of Thoroughbred racehorses; 75% of these horses having monthly tying-up episodes.

Results from a clinical trial conducted by the University of Minnesota, and research studies showed evidence that a horse's susceptibility to RER is inherited as an autosomal dominant trait; caused by an abnormality in intracellular calcium regulation.


Muscle stiffness
Rapid breathing
Reluctance to move for several hours
Short strides
Shifting hind limb lameness
Firm, painful hindquarter muscles
Elevated heart rate


  • History
  • Clinical signs
  • Physical exam
  • High serum levels of creatine kinase (CK) and aspartate aminotransferase (AST)
  • Urinalysis
  • Muscle biopsy

While waiting for your veterinarian

  • Do not move the horse until your vet arrives.


Diet managementModify diet to include less concentrated feed and more quality hay. Switch to a low sugar/ low starch feed. If needed, provide supplmental fat for increase of carbohydrate intake.
Exercise managementEnsure regular, consistent exercise without any days off and daily turnout.
Muscle relaxantsDantrolene and phenytoin
Pain reliving medicationBanamine or Bute
Tranquilizersto help control anxiety
FluidsProvided orally or intravenously


  • Diet: Feed horses a low sugar, low starch (NSC) grain with plenty of high quality hay. If needed, such as for performance horses, extra energy can be obtained by fat supplementation, in order to increase their carbohydrate intake.
  • Activity level: Ensure horses have daily turnout and consistent exercise.
  • Minimize stress and excitability: Turn out, feed, or exercising RER horses before other horses and providing pasture mates for comfort
  • Do not over supplement horses with more than the recommended amount of selenium in their diet

Scientific Research References

Good Overviews

Risk Factors

  • Genetics: Thoroughbred, Standardbred and Arabian horse breeds.
  • High-strung, female horses
  • Diet: Horses fed large amounts of sweet feed
  • Chronic lameness

Commonly Affected Breeds

Thoroughbred icon