These early characterizations of hyperthermia during and after exercise were largely examined through recording rectal temperature, but newer technologies like ingestible sensors ( 5– 7) and non-contact infrared thermography (IRT) ( 8) are enabling sensitive and alternative methods of measuring body temperatures (BTs) to monitor hyperthermia. Hyperthermia has been documented in dogs, in response to exercise at various durations and intensities, and is an important physiological measure of thermoregulation, heat stress risk, and a factor limiting performance during physical activity ( 1– 4). However, ear, and not eye, temperature is a better reflection of rectal temperature. This study demonstrates that IRT technology effectively measures both ear and eye temperature and enables effective monitoring of BT changes at rest, with exercise, and between breeds. Although BT readings were significantly related, method bias ( p < 0.02) was observed for BT eye to slightly underestimate BT rec, whereas no bias was observed between BT ear and BT rec. The relationship between BT eye and BT rec improved when monitoring exercise hyperthermia ( r = 0.674) versus measures at rest ( r = 0.381), whereas BT ear was significantly related to BT rec regardless of activity ( r = 0.615–0.735). Both BT ear and BT eye were significantly ( p < 0.0001) related to BT rec in all dogs with sedentary or exercise activity. All the three methods detected hyperthermia with Labs having a higher increase compared to Beagles. Time and breed interaction was significant in response to exercise for both BT rec and BT ear ( p = 0.035 and p = 0.005, respectively), with a marginal interaction ( p = 0.09) for BT eye. Total exercise (30-min) activity counts did not differ ( p = 0.53) between breeds. Readings also declined over time for BT eye ( p < 0.0001) and BT ear ( p < 0.0001), but not for BT rec ( p = 0.63) for both breeds. Sedentary BT differed by breed for BT rec ( p < 0.0001), BT ear ( p < 0.0001), and BT eye ( p = 0.06) with Labs having on average 0.3–0.8☌ higher BT compared to Beagles. Method differences were compared using Bland–Altman plots and linear regression. Each BT method was analyzed by analysis of variance for main effects of breed and time. BT rec, BT eye, and BT ear were measured within 5 min of the target time. Total exercise locomotor activity counts were recorded to compare relative intensity of play-exercise between breeds. BT measures were recorded at 09:00, 11:30, 12:30, and 02:30 from Labrador Retrievers ( N = 16) and Beagles ( N = 16) while sedentary and with 30-min play-exercise (pre- and 0, 15, 30-min post-exercise). Eye (BT eye) and ear (BT ear) temperature measured with infrared thermography (IRT) were compared to rectal (BT rec) temperature as the reference method and assess alternative sites to track hyperthermia, possibly to establish BT eye IRT as a passive and non-contact method. Rectal body temperature (BT) has been documented in exercising dogs to monitor thermoregulation, heat stress risk, and performance during physical activity. Nestlé Purina Research, St Louis, MO, USA.
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