Our objective was to evaluate the effect of conditioning and hypoxia on rectal and gastrointestinal temperature changes in dogs exercising at cold ambient temperature. Six Alaskan Husky sled dogs, each in a physically conditioned and unconditioned state, were used in the prospective study. Dogs in peak physical condition were run untethered on a treadmill under normoxic and hypoxic conditions of 20 and 12.5% environmental oxygen concentration, respectively, on separate days. After undergoing a deconditioning period of four months, the same dogs were run again under the same environmental conditions of 20 and 12.5% O2. Body temperature measurements were obtained via digital rectal thermometer and ingestible gastrointestinal thermistor at baseline, every 5 min for 30 min of exercise, and for 15 min following cessation of exercise. Under hypoxic conditions, peak gastrointestinal temperature was lower in conditioned vs unconditioned dogs. Gastrointestinal cooling was faster in conditioned dogs under normoxic conditions only. There was no difference in the peak rectal temperature, or rate of rectal temperature cooling in either normoxic or hypoxic conditions. 3 of 6 (50%) of the conditioned dogs reached a plateau temperature after approximately 20 to 25 min. This was observed less frequently when the dogs were unconditioned. Gastrointestinal and rectal temperatures reacted differently to exercise depending on conditioning or environmental oxygen concentration and this suggests that they cannot be used interchangeably to assess body temperature. Under these conditions, conditioning had no effect on rectal temperature. Presence of a plateau effect of rectal or gastrointestinal temperature may demonstrate a thermoregulatory balance of heat production and heat loss and may be a helpful measure in assessing individual dogs’ level of conditioning with regard to resistance to thermal stress.

30Although dark coat color in dogs has been theorized as a risk factor for thermal stress, 31 there is little evidence in the scientific literature to support that position. We utilized 16 non-32 conditioned Labradors (8 black and 8 yellow) in a three-phase test to examine effects of coat 33 color on thermal status of the dog. Rectal, gastrointestinal (GI), surface temperature, and 34 respiration rate measured in breaths per minute (bpm), were collected prior to (Baseline -phase 35 1) and immediately after a controlled 30-minute walk in an open-air environment on a sunny day 36 (Sunlight -phase 2). Follow up measurements were taken 15 minutes after walking (Cool 37 down -phase 3) to determine post-exposure return to baseline. No effect of coat color was 38 measured for rectal, gastrointestinal or surface temperature, or respiration (P > 0.05) in dogs 39 following their 30-minute walk. Temperatures increased similarly across both coat colors (rectal 40 1.88 • C and 1.83 • C; GI 1.89 • C and 1.94 • C; eye 1.89 • C and 1.94 • C; abdominal 2.93 • C and 41 2.35 • C) for black and yellow dogs respectively during the sunlight phase (P > 0.05). All 42 temperatures and respiration rates decreased similarly across coat colors for rectal (0.9 • C and 1.0 43 • C) and GI (1.5 • C and 1.3 • C) for black and yellow dogs respectively (P>0.05). Similarly, sex did 44 not impact thermal status across rectal, gastrointestinal or surface temperature or respiration rates 45 measured (P > 0.05). These data contradict the commonly held theory that dogs with darker coat 46 color may experience a greater thermal change when exposed to direct sunlight compared to 47 dogs with a lighter coat color.48 49

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Body temperature responses were recorded during phases of work (waiting-to-work in close proximity to search site, active work in a search site, and post-work recovery crated in vehicle) in human remains detection dogs during search training. State or federally certified human remains detection dogs (n = 8) completed eight iterations of searching across multiple novel search environments to detect numerous scent sources including partial and complete, buried, hidden, or fully visible human remains. Internal temperature (Tgi) of the body was measured continuously using an ingestible thermistor in the gastrointestinal tract. Mean total phase times were: waiting-to-work: 9.17 min (±2.27); active work: 8:58 min (±2:49); and post-work recovery: 24:04 min (±10.59). Tgi was impacted by phase of work (p < 0.001) with a small increase during active work, with mean peak temperature 39.4 °C (±0.34 °C) during that period. Tgi continued to increase for a mean of 6:37 (±6:04) min into the post-work recovery phase in the handler’s vehicle with a mean peak Tgi of 39.66 °C (±0.41 °C). No significant increase in temperature was measured during the waiting-to-work phase, suggesting behaviors typical of anticipation of work did not appear to contribute to overall body temperature increase during the waiting-to-work recovery cycle. Continued increase of gastrointestinal body temperature several minutes after cessation of exercise indicates that risk of heat injury does not immediately stop when the dog stops exercising, although none of the dogs in this study reached clinically concerning body temperatures or displayed any behavioral signs suggestive of pending heat injury. More work is needed to better understand the impact of vehicle crating on post-work recovery temperatures in dogs.

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