Thermal response to moderate exercise in dogs of different biotypes and brachycephalic obstructive airway syndrome severity assessed using infrared thermography

Introduction The aim of this study was to evaluate dogs of different skull conformations (cephalic biotypes) and Brachycephalic Obstructive Airway Syndrome (BOAS) grades subjected to two standardized moderate exercise tests, in order to determine their effects on infrared thermal responses in facial and appendicular thermal windows. Methods A total of 80 dogs were evaluated: dolichocephalic ( n = 20), mesocephalic ( n = 20), and brachycephalic ( n = 40), with the latter classified according to BOAS severity as G 1 ( n = 10), G 2 ( n = 18), and G 3 ( n = 12). Infrared thermal responses were evaluated in facial regions (caruncle, upper and lower eyelids, upper and lower lips, masseter, and nostril region) and appendicular regions (forelimbs, hindlimbs, gracilis, biceps femoris , and gastrocnemius muscles ). Measurements were obtained at four time points: T 1 , baseline; T 2 , after the 6-min walk test; T 3 , after the 1,000-meter walk test; and T 4 , following a 10-min recovery period. Results Brachycephalic dogs exhibited significant increases in facial surface temperature, reaching up to 2.6 °C ( p < 0.0001), and showed slower thermal recovery after 10 min. In G 2 dogs, muscular thermal windows showed post-exercise temperatures of 35 °C ± 0.5 °C. The 6-min walk test revealed significant differences in distance traveled among cephalic biotypes ( p = 0.0028). Furthermore, the 1,000-meter walk test revealed more pronounced alterations in superficial microcirculation in brachycephalic dogs across all BOAS grades. Discussion The greater facial thermal response and slower recovery observed in brachycephalic dogs suggest potential ventilatory limitations and increased reliance on cutaneous heat dissipation. The two exercise tests provided complementary information, with the 6-min walk test distinguishing differences in initial exercise performance and the 1,000-meter test revealing more pronounced thermal alterations associated with brachycephalic conformation and BOAS severity.