Subclinical hypernatraemia in a population of endurance racing sled dogs

Abstract

Electrolyte disturbances occur in both human and veterinary endurance athletes; however, hypernatraemia is poorly documented in dogs. To further explore electrolyte changes in canine endurance athletes, we collected blood from two teams of dogs (n=16) participating in the mid-distance (336 km) CanAm race. Serum samples were collected 36 hours before the start and within 20 minutes of race completion. Serum was similarly collected from 18 dogs withdrawn after completing 264 km. Biochemical profiles and aldosterone assays were performed. Mean serum sodium (>155 mEq/l) and corrected chloride concentrations were significantly increased (P<0.01) from baseline in finishing and withdrawn dogs; however, unlike sodium, corrected chloride concentrations remained within the reference interval. Serum phosphorous, hepatic enzymes, cholesterol, creatinine kinase, blood urea nitrogen, globulin, glucose, and iron concentrations were also significantly increased (P<0.01) compared to baseline in both finishing and withdrawn dogs. Both mean serum aldosterone and urea nitrogen concentrations were significantly increased (P<0.01) from baseline in finishing and withdrawn dogs, with finishers having greater concentrations than withdrawn dogs (P<0.01). Pre-race and matched finishing dog populations were then used for correlation analysis. Serum sodium concentrations were significantly (P<0.01) and strongly correlated with chloride (r=0.92), albumin (r=0.88), total protein (r=0.87), globulin (r=0.81), and potassium (r=0.86). Serum sodium concentrations were not significantly correlated with serum aldosterone concentrations (r=0.04, P=0.87). This study uniquely described subclinical hypernatraemia in the canine endurance athlete. The data lend support of dehydration through free water loss as a cause of hypernatraemia likely compounded by insufficient replenishment by drinking. Elevations in aldosterone concentrations in the face of hypernatraemia may be attributed to concurrent extra-renal hypotonic water losses, counter regulatory hormone influences, or physiological hyperthermia. Such findings demonstrate a degree of clinical tolerance for euvolemic driven hypernatraemia in endurance sled dogs, while highlighting the need for appropriate water supplementation.