Thermoregulatory Responses of Black-Coated Labrador Retrievers During Outdoor Walks Across a Gradient of Mean Radiant Temperature

Outdoor activity in tropical environments may challenge canine thermoregulation through exercise and radiant heat exposure. This study evaluated thermoregulatory responses of black-coated Labrador Retrievers during walks across naturally varying mean radiant temperature (MRT) conditions. Three healthy adult dogs completed 61 twelve-minute walks. Respiratory rate, rectal temperature, coat temperature, skin temperature, and paw pad temperature were recorded before, during, and after walking. Mixed-effects models accounted for repeated phases within walks and dog as a random effect, with MRT as a continuous explanatory variable. Significant Phase × MRT interactions occurred for respiratory rate, rectal temperature, skin temperature, and the rectal-to-skin temperature gradient, indicating that response magnitude depended on walking phase and radiant conditions. Coat temperature increased markedly with MRT during walking, whereas rectal temperature recovered more slowly during shaded rest. Change-from-pre-walk analyses accounted for physiological differences present before exercise. Increasing MRT was associated with greater thermoregulatory challenge during outdoor walks. Although the study included only three biologically independent dogs, repeated measurements revealed consistent physiological responses across a broad range of naturally occurring thermal conditions, informing assessments of canine welfare during outdoor activity.