Effect of reduced protein intake on endurance performance and water turnover during low intensity long duration exercise in Alaskan sled dogs

Increased nutritional demands for endurance exercise of dogs are typically met through increased amounts of their current food. As a result, protein intake is also increased, and excessive nitrogen may affect the dog's water balance. Sixteen unconditioned Alaskan sled dogs underwent a 6-week exercise training protocol, wherein 8 dogs were fed increasing amounts of their normal kibble to maintain body weight, while the other 8 were fed the same amount of kibble, with increasing calorie needs met by equal amounts of sugar and oil. The diets resulted in similar calorie intakes (181.3 +/- 20.0 and 205.7 +/- 36.3 kcal/kg(0.75), for the control and low protein dogs respectively) but control dogs had higher protein intakes (32.2 +/- 0.0 and 19.4 +/- 2.4% of metabolic energy intake). After 6 weeks of training the dogs completed a 5 day exercise test in which they travelled 24 km per day, where total energy expenditure was determined using doubly-labelled water technique. Dogs expended an average of 1,491 +/- 264 kcal/day (145 +/- 25 kcal/kg(0.75)/day), with no difference between the dietary treatments and no negative performance indicators. Following the exercise test the dogs underwent a 24 hour dehydration test (water withheld) followed by an 8 hour rehydration test (with ad libitum water intake recorded) where total body water was determined using deuterium oxide. Blood and urinary samples were also collected. Following exercise conditioning, control dogs had higher serum urea nitrogen than low protein dogs, and this as well as albumin decreased further during the 5 day exercise test. Low-protein dogs had lower overall total body water and higher fractional excretion of Na+, suggesting some renal adaptation. These findings suggest that reduced protein intake did not negatively affect athletic performance, though some facets of body chemistry were altered.