Thermal relations in sled dogs before and after exercise

Abstract

Regulation of internal body temperature (T_b), or thermoregulation, is an evolutionarily conserved trait that places demand on basal metabolic rate of endothermic animals. Across species, athletes generate increased quantities of heat in comparison to their nonathletic counterparts and, therefore, must mediate physiological unbalance by upregulating the effectiveness of their heat dissipation abilities. Canine athletes are no exception to this phenomenon, however, with literature denoting body temperatures lower than nonathletic canines, it is clear they must possess adaptations to mitigate this demand. With VO₂ max measurements of more than 200 mL/kg/min in sled dogs with mild training to 300 mL/kg/min in highly trained animals, sled dogs are a prime example of athleticism in canines. Seeking to determine correlations between T_ear and body mass, morphology, and age of canine athletes, core body temperature (T_b) was measured with an instant ear thermometer, using T_ear as a correlate before and after a 2-mile run. In addition, we employed thermal imaging analysis to capture body-wide heat dissipation patterns in sled dogs, and focused on thermal variation of mouth (T_mouth), nose (T_nose), and eyes (T_eye). Furthermore, we looked at correlations between thermal variability across these four tissues and head morphology of each dog. T_ear was consistently the highest temperature across all tissues measured, with a 1.5°C increase between pre- to postexercise (p < 0.001). Thermal imaging revealed significant positive correlations between T_mouth and body mass 15 min postexercise (p = 0.0023) as well as significantly negative correlations between T_nose and body mass at before exercise (p = 0.0468), T_eye and nose length after run (p = 0.0076), and T_mouth and nose length after run (p = 0.0110). As body temperature rises during exercise, it becomes increasingly important to regulate blood flow throughout the body to supply working tissues with oxygen. This demand is offset by the role of the snout in evaporative cooling through panting, functioning as a prime location for heat dissipation and therefore maintaining significant relationships with many other vascularized tissues.