Effect of different masses, ages, and coats on the thermoregulation of dogs before and after exercise across different seasons.

ABSTRACT

Domestic dogs demonstrate a positive correlation between body mass and whole-animal metabolism but a negative relationship between body mass and lifespan in dogs. Additionally, essential physiological mechanisms in domestic dogs, such as the relationships between thermal relations and body size and age, remain poorly understood. In this study, we looked at thermoregulation in dogs of different sizes, ages, coat types, and head morphologies across three different seasons. We used tympanic membrane temperatures (Tear) and infrared thermography to observe temperature regulation in pet dogs before and after a 45-min moderate walking exercise trial. We hypothesized that Tear and heat dissipation is positively correlated with body mass. Using network analysis, we found that body mass was among the most central features for spring and summer trials, but not for the winter trials. Similarly, leg length, snout length, and paw width were the central predictors in two of the three seasons. Mediation analysis demonstrated that nose and snout length act as significant mediators of the effects of body mass on mouth temperatures in the spring. For the summer trials, nose length and paw width significantly mediated the effect of body mass on mouth temperatures. Age, however, does not seem to be a major determinant of thermoregulation in dogs according to best subset models. A cross-seasonal examination of repeated measurements showed that mouth temperature heat dissipation rates decreased with increasing temperature and humidity. Overall, our findings support our hypothesis that Tear and heat dissipation rates are positively correlated with body mass in dogs, thus, negatively correlated with mass-specific metabolism. This finding suggests that small dogs allocate a bigger proportion of their metabolism to "inefficiencies" of heat production to offset greater heat loss.