Background: The endurance sled dog is the ultimate endurance athlete in which to examine the exercise-associated acute phase and myokine responses that might be related to changes in muscle metabolism and damage. An inciting cause for increased C-reactive protein has yet to be elucidated, which might involve interleukin-6 and other myokines.Objectives: To examine concentrations of interleukin-6 (IL-6), interleukin-15 (IL-15), interleukin-8 (IL-8), and tumor necrosis factor-a (TNF-a), and markers of the inflammatory response of exercise; monocyte chemoattractant protein-1 (MCP-1) and C-reactive protein (CRP) before, during, and after an endurance racing event.Animals: 26 sled dogs completing a 1650-km race.Methods: In a prospective study, cephalic venipuncture was performed before racing, at the midpoint, and after racing. Body weight and serum CRP, MCP-1, IL-15, IL-8, IL-6, and TNF-a concentrations were evaluated using enzyme-linked immunoabsorbance-based assays or a luminex multiplex assay.Results: There were no significant differences in concentrations of IL-6, IL-15, IL-8, or TNF-a at the 3 time points, whereas there were significant increases in MCP-1 (median and range-start: 86 pg/mL ; midpoint: 179 pg/mL ; finish: 180 pg/mL [21-1294]; P < .01) and CRP (median and range-start: 18 lg/mL ; midpoint: 76 lg/ mL ; finish: 60 lg/mL [12-170]; P < .01) at the midpoint and race finish. There was a significant linear relationship between MCP-1 and IL-6 (R = 0.68; P < .01).Conclusions and Clinical Significance: The inflammatory response to exercise increases as measured by MCP-1 during and after endurance exercise in sled dogs. IL-6 appears to be associated with MCP-1; however, the reasons for increases in the acute phase response (CRP) cannot be attributed to IL-6 or other myokines. IL-6 and MCP-1 concentrations might be useful in future investigations of exertional rhabdomyolysis.

Sled dogs are known to develop numerous serum biochemical changes due to endurance exercise. Previous studies have suggested that mild hyponatraemia and hypokalaemia can develop during endurance racing. The aim of the present study was to determine if serum biochemical alterations are similar to previous reports, and if electrolyte alterations are still present with present feeding practices utilised by mushers. Serum chemistries were obtained from 26 Alaskan Huskies belonging to 3 different teams, before and after a 1600 km race. Meals and snacks were analysed via calculation to determine daily macronutrient and electrolyte intake. Numerous biochemical alterations were observed including significant differences in serum total protein, albumin, globulin, aspartate aminotransferase, creatine kinase, TAG, NEFA and urea nitrogen (P < 0·05). Serum electrolyte status revealed a mild, yet significant decrease in serum sodium (P = 0·002); and serum potassium was not significantly different (P = 0·566). Further examination of the sodium intake across the three teams revealed two teams with an average daily intake of approximately 8·5 g/dog/d (700 mg/4184 kJ) and the other team consuming 11·1 g/dog/d (1200 mg/4184 kJ). Regression analysis shows a significant modest positive correlation between serum sodium decrease and sodium intake per metabolic body weight of the dogs, as well as a modest positive correlation between sodium intake and serum potassium implicating the renin–angiotensin aldosterone system as a major factor involved in sodium and potassium homoeostasis. These findings suggest that consumption of approximately 0·9 g/kg0·75 (1·2 g/4184 kJ) of sodium per d may prevent exercise-induced decreases in sodium and potassium.

Endurance sled dogs have unique dietary energy requirements. At present, there is disparity in the literature regarding energy expenditure and thus energy requirements of these dogs. We sought to further elucidate energy requirements for endurance sled dogs under field conditions. Three sled dog teams completing the 2011 Yukon Quest volunteered to provide diet history. Nutritional content was evaluated and a mock meal was analysed for each team. Race data were obtained from . Dogs were weighed at the start of the race in Whitehorse Yukon (WH), a mid-way checkpoint in Dawson Yukon (DS) and at the finish in Fairbanks Alaska. Data are average value per dog or per dog per d. Linear regression compared average weight loss to average kcal/dog consumed daily. Diets and feeding regimes were similar for all three teams. The average daily energy intake and nutrient content was similar for all diets. During leg one (WH to DS), team 1 gained weight overall, whereas the other two teams experienced weight loss. Linear regression revealed 37 638 kJ/dog/d (8995 kcal/dog/d) was required for weight maintenance. During leg two (DS to Fairbanks Alaska), average weights decreased for all three teams. The extrapolated kcal requirement was approximately 57 734 kJ/dog/d (13 799 kcal/dog/d). The carbohydrate contents of these diets also suggest that presumed fat intake for endurance sled dogs may be slightly less than previously thought. Finally, these data support the concept that dietary energy requirements vary substantially with additional variables such as load pulled, terrain and ambient temperature.

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