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Equine Vet J. 2015 Mar;47(2):165-70. doi: 10.1111/evj.12255. Epub 2014 May 19.

Prevalence of exertional rhabdomyolysis in endurance horses in the Pacific Northwestern United States.

Author information

1
Department of Clinical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, Oregon, USA.

Abstract

REASONS FOR PERFORMING STUDY:

Exertional rhabdomyolysis (ER) is a reported syndrome in competing endurance horses; however, the prevalence and cause of ER in this population have not been defined.

OBJECTIVES:

To determine the prevalence of ER in a sample of endurance racing horses and investigate factors, including relevant genetic defects, contributing to the occurrence of rhabdomyolysis in this group.

STUDY DESIGN:

Prospective clinical study.

METHODS:

Riders of 101 horses participating in one of four 50-mile (80.5 km) distance races completed a comprehensive questionnaire regarding the medical history, management and performance of their horse. Serum creatine kinase activity (CK) was measured before and 4 h after completion of exercise. Hair samples were analysed by PCR for the R309H mutation in the glycogen synthase gene (GYS1) responsible for type 1 polysaccharide storage myopathy (PSSM) and the C7360G mutation in the ryanodine receptor 1 (RYR1) gene causing malignant hyperthermia (MH).

RESULTS:

Samples were obtained from 68 Arabians, 20 half-Arabians and 13 horses of other breeds. Serum CK was above the resting reference interval (145-633 u/l) in 38 horses after racing (median 883 u/l, range 658-3739) but was compatible with values previously reported in apparently healthy endurance horses. Pathological ER was suspected to occur in 4 horses with serum CK activities exceeding 10,000 u/l 4 h after racing (median 84,825 u/l; range 10,846-381,790) including 3 Arabians and one half-Arabian horse. GYS1 and RYR1 mutations were not present in hair samples from any horses.

CONCLUSIONS:

Exertional rhabdomyolysis occurred at a prevalence of 4.0% in a sample of horses participating in 50 mile distance events and all affected horses were Arabian or half-Arabian. The cause of ER in the endurance horse population remains unknown; however, ER in competing Arabian endurance horses is unlikely to be due to type 1 PSSM or MH.

KEYWORDS:

exercise; exertional rhabdomyolysis; horse; polysaccharide storage myopathy

PMID:
24579562
DOI:
10.1111/evj.12255
[Indexed for MEDLINE]

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