Energy metabolism of Inuit sled dogs.

We explored how seasonal changes in temperature, exercise and food supply affected energy metabolism and heart rate of Inuit dogs in Greenland. Using open flow respirometry, doubly labeled water, and heart rate recording, we measured metabolic rates of the same dogs at two different locations: at one location the dogs were fed with high energy food throughout the year while at the other location they were fed with low energy food during summer. Our key questions were: is resting metabolic rate (RMR) increased during the winter season when dogs are working? Does feeding regime affect RMR during summer? What is the proportion of metabolic rate (MR) devoted to specific dynamic action (SDA), and what is the metabolic scope of working Inuit sled dogs? The Inuit dogs had an extremely wide thermoneutral zone extending down to -25 degrees C. Temperature changes between summer and winter did not affect RMR, thus summer fasting periods were defined as baseline RMR. Relative to this baseline, summer MR was upregulated in the group of dogs receiving low energy food, whereas heart rate was downregulated. However, during food digestion, both MR and HR were twice their respective baseline values. A continuously elevated MR was observed during winter. Because temperature effects were excluded and because there were also no effects of training, we attribute winter elevated MR to SDA because of the continuous food supply. Working MR during winter was 7.9 times the MR of resting dogs in winter, or 12.2 times baseline MR.