Sled dogs undergo extreme metabolic demands during an ultra-distance race. These demands result in electrolyte derangements that can be associated with exertional rhabdomyolysis (ER). An observational cohort study was conducted during the 2019 Yukon Quest 300 race. Blood was drawn and will be analyzed to evaluate hormone concentrations (renin, aldosterone, ADH), and serum biochemistry with specific interests in creatine kinase, sodium, potassium, phosphorus and chloride concentrations. Urinalysis, including urine electrolytes, creatinine, and myoglobin (if collected during clinical presentation) will be investigated as well. Our specific aims in this study are to identify dogs with clinical ER in the field and compare their serum electrolyte status to those dogs dropped for other reasons and those completing the race. Ultimately, we aim to expand upon the hypothesis that electrolyte abnormalities, especially potassium depletion, may contribute or cause clinical ER in sled dogs as well as expand upon the mechanism underlying these electrolyte differences.