Prevalence of exertional rhabdomyolysis in endurance horses in the Pacific Northwestern United States.
Authors: Wilberger M S, McKenzie E C, Payton M E, Rigas J D, Valberg S J
Journal: Equine veterinary journal
Summary
Exertional rhabdomyolysis (ER) represents a significant concern for endurance competitors, yet its true prevalence and aetiology in racing horses remain poorly understood. Wilberger and colleagues recruited 101 horses competing in 50-mile distance events across the Pacific Northwest, collecting serum creatine kinase measurements both at rest and 4 hours post-exercise alongside genetic screening for two established myopathies: type 1 polysaccharide storage myopathy (PSSM, caused by the GYS1 R309H mutation) and malignant hyperthermia (RYR1 C7360G mutation). Pathological ER—defined as serum CK exceeding 10,000 u/l—was identified in 4 of 101 horses (4.0% prevalence), all of which were Arabian or half-Arabian breed; notably, whilst 38 horses showed post-exercise CK elevation above resting reference values (median 883 u/l), these levels remained consistent with healthy endurance horses and did not indicate clinical disease. Neither the GYS1 nor RYR1 mutations were detected in any study participants, effectively ruling out PSSM type 1 and malignant hyperthermia as causative factors in this population. For practitioners managing Arabian endurance athletes presenting with muscle dysfunction, this work suggests ER aetiology requires investigation beyond common genetic myopathies, prompting consideration of nutritional, electrolyte, training and metabolic factors as potential contributors to this breed-specific condition.
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Practical Takeaways
- •Veterinarians managing Arabian and half-Arabian endurance horses should maintain heightened awareness of ER risk; if a horse shows signs of muscle damage post-exercise, serum CK testing is warranted to distinguish normal post-exercise elevation from pathological rhabdomyolysis.
- •Genetic testing for GYS1 and RYR1 mutations is unlikely to identify ER cases in Arabian endurance horses; investigation should focus on other potential metabolic, nutritional, or management factors.
- •Trainers and riders of Arabian endurance horses experiencing recurrent muscle soreness or poor recovery should consult veterinarians to rule out ER and explore alternative causes such as training intensity, electrolyte balance, or conditioning protocols.
Key Findings
- •Exertional rhabdomyolysis occurred in 4.0% (4/101) of endurance horses competing in 50-mile distance races, with all affected horses being Arabian or half-Arabian breeds.
- •Pathological ER was identified by serum CK activity exceeding 10,000 u/l at 4 hours post-exercise (median 84,825 u/l; range 10,846-381,790).
- •Neither GYS1 mutation (causing type 1 PSSM) nor RYR1 mutation (causing malignant hyperthermia) were detected in any of the 101 horses studied.
- •The etiology of ER in Arabian endurance horses remains unknown, as the study ruled out two major genetic myopathies previously implicated in other equine populations.