A comparison of black vs. yellow coat color on rectal and gastrointestinal temperature in Labrador retrievers

Although dark coat color in dogs has been theorized as a risk factor for heat injury, there is little evidence in the scientific literature to support that position. We utilized 16 non-conditioned Labradors (8 black and 8 yellow) in a three-phase test to examine effects of coat color on thermal status of the dog. Rectal, gastrointestinal (GI), and surface temperature using infrared thermography measured at the eye and abdomen, were measured along with respiration rate measured in breaths per minute (bpm), collected at three time points. Phase 1 (Baseline) - 30 minutes of crate rest in a climate-controlled room; Phase 2 (Walking in Sunlight) -30-minute walk in an outdoor environment on a sunny day; and Phase 3 (Cooling) - 15 minutes of crate rest in climate-controlled room to determine post-exposure recovery temperatures. No effect of coat color was measured for rectal, gastrointestinal, surface temperature, or respiration rate (P > 0.05) in dogs following their 30-minute walk in sunlight. All temperatures measured increased similarly (rectal 1.86 degrees C and 1.80 degrees C; GI 1.92 degrees C and 1.95 degrees C; eye 2.8 degrees C and 1.92 degrees C; abdomen 2.91 degrees C and 2.39 degrees C) in black and yellow dogs respectively, following 30 in Sunlight ( P > 0.05). Additionally, temperatures decreased in a similar fashion for both coat colors (rectal 0.84 degrees C and 0.88 degrees C; GI 1.48 degrees C and 1.32 degrees C; eye 1.49 degrees C and 1.70 degrees C; abdominal 1.75 degrees C and 1.5 degrees C) in black and yellow dogs respectively ( P > 0.05) during Cooling. Respiration rate increased similarly for both coat colors, (147.2 bpm and 143.7 bpm for black and yellow respectively) when Baseline values were compared to Sunlight values and decreased similarly (28.8 bpm black; 60.2 bpm yellow after Cooling phase ( P > 0.05). These novel data reveal a surprising lack of effect for black vs. yellow coat color on body temperature as measured by standard rectal thermometer, gastrointestinal thermistor, or infrared thermography in a population of Labrador retrievers. (c) 2021 Elsevier Inc. All rights reserved.