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1
1
2
3
4The effect of light vs dark coat color on thermal status in
5Labrador Retriever dogs.
6
7
8Authors:
9Caitlin Neander1, Janice Baker2, Kathleen Kelsey3, Jean Feugang4, Erin Perry1*
10
11 Affiliations:
12 1Department of Animal Science, Food and Nutrition, College of Agriculture Science, Southern
13 Illinois University, Carbondale, IL
14 2Veterinary Tactical Group, Vass, NC 28394
15
16 3Working Dog Enterprises, Sturgeon, MO 65284
17
18 4Department of Animal and Dairy Science, College of Agriculture and Life Sciences, Mississippi
19 State University, Mississippi State, MS
20
21
22 * Corresponding author: erin.perry@siu.edu
23
24
25
26
27
28
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2
29 Abstract
30
Although 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
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2.35 ◦C) for black and yellow dogs respectively during the sunlight phase (P > 0.05). All
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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
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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
Keywords: Canine, Labradors, Thermal Stress, Heat Stress, Dog, Thermal Imaging,
50
Temperature, Coat Color
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51
52 Introduction
53
Darker coat color has been suggested as a potential risk factor for heat injury in dogs in
54
several publications [1-4] However, little evidence is available to support this theory, and a
55
majority of these claims appear in the introduction or discussion sections of publications, or in
56
review articles, with no supporting data. One study in Greyhounds reported higher rectal
57
temperatures in darker colored dogs following exercise but utilized greater numbers of males in
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the darker coat participant group. These males were significantly larger in size than their female
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cohorts, so it is not known if sex or size played a role in their results. In addition, the darker
60
colored group (n = 166) had more than twice the number of the light coated group (n = 63)
61
which may have
impacted the outcome [5]. In another study using Newfoundland dogs, researchers
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tested patches of white and black fur exposed to heat lamps. Authors measured the microclimate of the
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dog’s coat and reported no significant difference in temperature between white and black fur regions
64
on the dogs [6]. However, this study did not examine two separate groups of dogs with single coat
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colors (i.e. solid black or white).
66
Work in cattle has demonstrated an impact on thermal status associated with coat color, but
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this has not been thoroughly investigated in dogs. Increased solar absorption in darker coated cattle
68
has been demonstrated to increase overall heat gain [7]. Darker cattle exposed to direct sunlight had a
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surface temperature gain of 4.8 ◦C, while lighter cattle only increased surface temperature by 0.7◦C
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[8]. Additionally, this study reported increased incidence of elevated surface temperature, respiration,
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sweating, and heat stress signals in darker colored cattle compared to lighter colored cattle.
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The risk of thermal injury to dogs is of significant concern to the veterinary community and is
73
considered a common occurrence especially during the summer months. Evidence to validate the
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4
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ideas surrounding coat color as a risk factor would be helpful in establishing a better understanding of
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any increased danger facing dark coated dogs. Assessment of risk for heat injury can only be
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accurately evaluated by studying dogs that incur heat injury in comparison to dogs that do not,
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whether prospectively or retrospectively. Prospective studies of this nature are inherently difficult to
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conduct as our current standards of ethics and animal stewardship generally preclude experimentally
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induced heat injury in dogs. In addition, given the relatively low incidence of naturally occurring heat
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injury in any given population of dogs, prospective studies relying on naturally occurring cases would
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require a significant amount of time to complete. Thus, risk of heat injury is primarily based on
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observations of normal thermoregulatory reactions to safe levels of thermal stress, typically induced
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by exercise. In this study, we exposed dogs of light and dark coat colors to mild exercise (i.e. loose
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leash walk) in direct sunlight to assess thermoregulatory reactions and measure various parameters
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associated with body temperature and thermoregulation. The objective of this research was to identify
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the impact of coat color on the thermal status of dogs exposed to direct sunlight and to measure the
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increase in temperature experienced by black dogs as compared to yellow dogs.
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89 Materials and Methods
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Animals and Diets
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Institutional Animal Care and Use approval (protocol #18-022) was received from
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Southern Illinois University prior to initiation of the study. The study was conducted in
mid-
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June in Carbondale, Illinois with seasonally typical environmental conditions (mean
outdoor
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temperature 29.34±1.76 ◦C, 84.81±3.17 ◦F). Non-conditioned Labrador Retrievers (n = 16)
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from a single kennel and with similar genetics were recruited for
participation in this study.
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“Non-conditioned” was determined as having daily exercise
consisting of 4±1 hours of daily
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group turnout but the absence of a specific conditioning or exercise program. All dogs
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utilized came from 2 litters to limit for genetic variability. Dogs had a mean age of 2.73±1.86
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years, mean weight 26.6±
3.32 kg and a mean BCS of 5.5±1.5. Study participants were maintained
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on a commercial kibble diet (Victor High Energy, Mid America Pet Food Mount Pleasant, Texas)
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and fed twice daily for 60 days prior to the study. All dogs were up to date on vaccinations (rabies,
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bordetella, DHLPP) and received a monthly standardized parasite control regimen (Frontline Plus,
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Merial France) (Interceptor Plus, Elanco, Greenfield, IN). All study participants received a health
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screening by a licensed veterinarian prior to inclusion in the study and were also assigned a body
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condition score (BCS) by a trained researcher (Nestle Purina Petcare Company, St. Louis, MO).
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Following this exam, one canine was excluded from participation due to a previously undiagnosed
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dermal condition. Dogs of opposite colors were paired according to sex and BCS for participation.
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Phases
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The study was separated into three phases. Phase 1 (Baseline) included housing of each dog
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for 30 uninterrupted minutes in a climate-controlled room in individual crates. Phase 2 (Sunlight)
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consisted of 30 minutes of loose leash walking at a controlled pace in an uncovered outdoor sandy
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arena measuring 30m by 60m. The study concluded with Phase 3 (Cooling) and incorporated a 15-
113
minute rest in a climate-controlled room in individual crates. All dogs were monitored throughout the
114
study by veterinary staff stationed in the center of the outdoor arena and climate-controlled holding
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area, and all dogs were allowed ad libitum access to water while in their crates during both the
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Baseline and Cooling phases of the study.
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Environmental conditions in the outdoor arena and in the climate-controlled room were
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monitored (Accurite Wireless Weather Station, Chaney Instrument Co. Lake Geneva, WI) to record
119
temperature, humidity and heat index every five minutes.
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Data Collection
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Thermal status data for each dog were captured immediately following each of the three
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phases utilizing four methods as shown in Fig 1.
Gastrointestinal (GI) data were captured using an
123
ingestible thermistor orally administered (CorTemp, CorTemp Inc, Palmetto, FL) 30 minutes
124
(±15) prior to the Baseline phase. GI temperatures were monitored with a handheld wireless
125
reader (CorTemp, HQInc Palmetto, FL.). GI temperature was recorded in triplicate for each data
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collection period to ensure accuracy and the mean was utilized for statistical analysis. Rectal
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measurements were collected in tandem, using calibrated, 8second digital thermometers
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(American Diagnostics Company ADTEMP II model #413B) inserted to a depth of
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approximately 2 cm with petroleum jelly to minimize canine discomfort. Thermal images of
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participants were captured using a forward-looking infrared thermal camera (FLIR T400 thermal
131
camera) at an approximate distance of 2 meters from the canine to capture body surface
132
temperature as previously
described [9-12] . To reduce the effects of environmental factors, all
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images were captured in an enclosed area with no exposure to wind or direct sunlight. Thermal
134
images were analyzed using thermography software (ThermaCam Researcher Professional 2.9,
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FLIR Systems Inc. Wilson, OR, USA) to determine body surface temperature at the left eye
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and caudal abdomen as described
previously [13-15] with examples shown in Fig 2.
137
138
Fig 1. Pictogram representing the phases and points of data collection.
139
140
141 Fig 2. Thermography1 depicting Baseline2 (left) and Sunlight3 (right) values for Labrador Black
142 6. The two areas of interest were left eye4 and left caudal abdomen5.
143
144
145
Digital video was utilized to record respiration rates (GoPro Camera, GoPro Inc. San
146
Mateo, Ca) for 30 seconds at the start of each data collection period prior to rectal temperature
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147
monitoring. The head, face, and tongue were captured and later played back in slow motion to
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count respiration during this 30 second period. A single independent observer was utilized
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throughout all canine respiration videos to minimize observer bias. Respiration was calculated as
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breaths per minute (BPM) = 30-second respiration x 2.
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Statistical Analysis
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All data were analyzed using SAS version 9.4 (SAS Institute Inc., Cary, NC). Each
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phase (baseline, sunlight, cooling) was examined using a Proc Glm repeated measures test.
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Baseline and Sunlight temperatures were examined using a paired t test to identify main effects
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of coat color and sex for dependent variables including rectal, gastrointestinal, surface
156
temperature, respiration rate, and water consumption.
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Additionally, a multivariate ANOVA was utilized to identify differences associated with the
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interactions of coat color and sex on rectal, gastrointestinal, body surface temperature,
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respiration, and water consumption. Water consumption throughout the data collection period
160
was calculated as:
Water offered – Water remaining = Water consumed
161
Return to baseline was identified as having achieved a cooling phase temperature within 0.5◦F of the
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dog’s initial baseline temperature using the below equations. If the cooling phase temperature had
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fallen to within 0.5◦F, it was deemed “yes” the dog returned to a baseline temperature. The following
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equation was utilized:
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Baseline – Cooling ≤ 0.5◦F = Return to Baseline (Yes)
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Baseline – Cooling ≥ 0.5◦F = Return to Baseline (No)
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Return to baseline was reported as Yes or No and was analyzed using the Proc Freq procedure of SAS
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(chi square) to examine differences coat color and sex. Significance for all outcomes was established
169
at
P
<
0.05.
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170
171 Results
172
Following 30 minutes of walking in direct sunlight, rectal temperatures increased by 1.88
°
C in
173
black dogs, and 1.83 ◦C in yellow coated dogs (P< 0.0001). Similarly, GI temperatures
174
increased by 1.89 ◦C in black coated dogs, and 1.94 ◦C in the yellow group, (P < 0.0001) as
175
shown in Fig 3. Eye surface temperature increased by 2.8 ◦C black and 1.93 ◦C yellow (P <
176
0.005) and abdominal surface temperature increased by 2.93 ◦C black and 2.35 ◦C yellow (P <
177
0.0001). See Figs 3-4, Table 1. No significant temperature difference was noted between black
178
and yellow Labradors across all phases.
179 Fig 3. Mean change in rectal1 and gastrointestinal temperature (GI)2 across three phases in non-
180 conditioned Labradors.
181
182 Fig 4. Mean change in body surface temperature measured by thermography1 at the eye2 and
183 abdomen3 in non-conditioned Labradors
184
185 Table 1. Mean values of thermal status indicators1 across three phases (Baseline2, Sunlight3, Cooling4) in
186 Labradors grouped by coat color.
Variable
Color
Baseline
P-value
Sunlight
P-value
Cooling
P-value
Black
38.44±0.37 °C
a
101.2±0.7 °F
40.3±0.41 °C b
104.5±0.8 °F
39.46±0.34
°Cc
103±0.6 °F
Rectal5
Yellow
38.51±0.52 °C
a
101.3±1.0 °F
0.8404
40.31±0.34 °C
b
104.6±0.6 °F
0.9354
39.43±0.30
°Cc
102.8±0.4 °F
0.4673
Black
38.76±0.25 °C
a
101.8±0.5 °F
40.68±0.47 °C
b
105.2±0.9 °F
39.2±0.6 °Cc
102.6±1.1 °F
GI6
Yellow
38.66±0.48 °C
a
101.6±0.9 °F
0.6279
40.61±0.21°C
b
105.1±0.4 °F
0.8286
39.29±0.26
°Cc
102.6±0.5
°Cc
0.8153
Eye7
Black
36.09±0.57 °C
a
97.0±1.1 °F
0.0934
38.89±0.42 °C
b
102.0±0.8 °F
0.3004
37.4±0.5 °Cc
99.3±0.96 °F
0.0973
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187
188 ∗Notes a significant difference observed by coat color
189 a,b,cNotes a significant difference observed by phase
190 1Thermal status indicators including rectal, gastrointestinal, eye and abdominal temperature
191 2Baseline occurred 30 minutes prior to sunlight exposure (sunlight) and recorded initial measurements
192 3Sunlight phase consisted of 30 minutes of active walking in a sunny outdoor area on a leash
193 4Cooling phase occurred 15 minutes after walking in a climate-controlled room with water
194 5Rectal temperature was recorded by inserting thermometer to a depth of approximately 2 cm with
195 petroleum jelly
196 6GI (gastrointestinal) temperature was recorded with an ingestible thermistor CorTemp 30 minutes prior
197 to baseline
198 7Eye temperature was captured using thermography FLIR T400 at the left eye
199 8Abdominal temperature was captured using thermography FLIR T400 at the left caudal abdomen
200 9Respiration rate was captured for 30 seconds utilizing a GoPro, depicted as breaths per minute (bpm)
201
202
Similarly, all temperature measurements significantly decreased from sunlight to cooling
203
phase. Following cessation of cooling phase, rectal temperatures decreased by 0.84
◦C black and 1.0
204
◦C yellow (P< 0.0001) and GI temperatures decreased 1.45 C in black dogs and 1.33 in yellow
205
dogs (P< 0.0001) as shown in Fig 3. Thermal eye surface temperature decreased 1.49 ◦C in black
206
and 1.71 ◦C in yellow dogs (P < 0.005), and abdominal surface temperature decreased by 1.0 ◦C
207
black and 0.85 ◦C yellow (P < 0.0001) as shown in Fig 4. A similar change in respiration rates
208
was shown across both coat colors of Labradors, meaning that coat color did not significantly
209
impact breathing rates across phases (P > 0.05), as shown in Fig 5.
210
211 Fig 5. Mean change in respiration rates1 across three phases in non-conditioned Labradors.
212
213
Yellow
36.68±0.55 °C
a
98.0±1.1 °F
38.6±0.54 °C b
101.5±1.0 °F
36.9±0.51
°Cc
98.4±1.0 °F
Black
36.24±0.91 °C
a
97.2±1.7 °F
39.15±0.73 °C
b
102.5±1.4 °F
37.4±0.5 °Cc
100.7±1.3 °F
Abdominal8
Yellow
36.01±1.44 °C
a
96.9±2.9 °F
0.7763
38.4±0.75 °C b
101.1±1.5 °F
0.0908
36.9±0.51
°Cc
99.6±1.2 °F
0.1002
Black
123.3±20.5a
270.5±40.2b
241.7±24.5c
Respiration9
Yellow
132.9±40.7a
0.7206
276.6±28.2b
0.744
216.4±59.7c
0.2998
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214
Exposure to walking in sunlight significantly increased the rectal (1.84◦C), GI (1.94◦C), eye
215
surface (2.41◦C) and abdominal surface (2.67◦C) temperatures of all dogs
when Baseline and
216
Sunlight temperatures were compared (P < 0.0001). Furthermore, returning to the climate-
217
controlled room significantly decreased the rectal (0.7◦C), GI (1.41◦C), eye surface (1.58◦C), and
218
abdominal surface (0.92◦C) temperature of all dogs (P < 0.0001).
219
220
After completion of 30 minutes in direct sunlight walking, both males and females saw a similar
221
increase across all temperatures, rectal (1.83◦C male, 1.84◦C female), GI (2.04◦C male, 1.87◦C
222
female), eye surface (2.3◦C 2 male, 2.5◦C female) and abdominal surface (2.93◦C male and 2.5
223
◦C female). A similar fall in temperatures for both sexes was seen after 15 minutes of passive
224
cooling, rectal (0.92◦C male, 0.89◦C female), GI (1.32◦C male, 1.47◦C female), eye surface
225
(1.62◦C male, 1.57◦C female), and abdominal surface (1.0◦C male, 0.87◦C female) as shown in
226
Figures 6-7, Table 2.
227
228 Fig 6. Mean change in rectal1 and gastrointestinal temperature (GI)2 across three phases in non-
229 conditioned Labradors.
230
231 Fig 7. Mean change in surface temperature measured by thermography1 at the eye2 and
232 abdomen3 in non-conditioned Labradors across three phases.
233
234
Table 2. Mean values of thermal1 status indicators across three phases (Baseline2,
235
Sunlight3, Cooling4) in Labradors grouped by sex.
VARIABLE
SEX
BASELINE
P-
VALUE
SUNLIGHT
P-VALUE
COOLING
P-
VALUE
Male
38.52±0.35 °C a
101.3±0.7°F
40.35±0.31 °C b
104.6±0.6 °F
39.43±0.3 °Cc
103±0.6 °F
RECTAL5
Female
38.44±.5 °C a
101.2±0.9 °F
0.8536
40.28±0.41 °C b
104.5±0.8 °F
0.6991
39.39±0.27 °Cc
102.9±0.5 °F
0.7511
Male
38.68±0.36 °C a
101.7±0.7 °F
40.72±0.21 °C b
105.3±0.4 °F
39.4±0.41 °Cc
102.9±0.8 °F
GI6
Female
38.73±0.39 °C a
101.7±0.7 °F
0.9407
40.6±0.44 °C b
105.1±0.9 °F
0.6005
39.13±0.49 °Cc
102.4±0.9 °F
0.3736
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236
237 ∗Notes a significant difference observed by sex
238 a,b,c Notes a significant difference observed by phase
239 1Thermal status indicators including rectal, gastrointestinal, eye and abdominal temperature
240 2Baseline occurred 30 minutes prior to sunlight exposure (sunlight) and recorded initial measurements
241 3Sunlight phase consisted of 30 minutes of active walking in a sunny outdoor area on a leash
242 4Cooling phase occurred 15 minutes after walking in a climate-controlled room with water
243 5Rectal temperature was recorded by inserting a thermometer rectally 2cm
244 6GI (gastrointestinal) temperature was recorded with an ingestible thermistor CorTemp 30 minutes prior to baseline
245 7Eye temperature was captured using thermography FLIRT400 at the left eye
246 8 Abdominal temperature was captured using thermography FLIR T400 at the left caudal abdomen
247 9Respiration rate was captured for 30seconds utilizing a GoPro, depicted as breaths per minute(bpm)
248
249
250
Across all phases of the study, sex did not show a significant effect on respiration rates
251
of the Labradors, with both sexes showing a similar increase and decrease in bpm (P > 0.05), as
252
shown in Fig 8.
253
254 Fig 8. Mean change in respiration rates1 across three phases in non-conditioned Labradors.
255
256
257
No effect of coat color (P = 0.5560) or sex (P = 0.9806) was seen for water consumption
258
with black dogs consuming 173.75± 195.3 ml and yellow dogs consuming
259
221.21±57.1 ml.
260
261
No effect of coat color was noted when rectal temperatures were examined for a return to
262
baseline in 12.5% and 28.6% of black and yellow dogs respectively, (P
= 0.5692). Similarly, GI
263
temperatures returned to baseline 50% of black and 42.9% of yellow dogs (P = 1.00) and
264
abdominal surface temperature with 12.5% black and 28.6% yellow dogs (P = 0.6080) returning
Male
36.58±0.64 °C a
97.9±1.3 °F
38.9±0.14 °C b
102.0±0.3 °F
37.28±0.5 °Cc
99.1±1.0 °F
EYE7
Female
36.16±0.57 °C a
97.1±1.1 °F
0.2509
38.66±0.62 °C b
101.6±1.2 °F
0.3087
37.09±0.59 °Cc
98.8±1.1 °F
0.5457
Male
36.2±0.95 °C a
97.2±2.0 °F
39.13±0.34 °C b
102.4±0.7 °F
38.13±0.45 °Cc
100.6±0.9 °F
ABDOMINAL8
Female
36.09±1.33 °C a
97.0±2.5 °F
0.8360
38.58±0.97 °C b
101.4±1.9 °F
0.1674
37.71±0.81 °Cc
99.9±1.5 °F
0.9533
Male
124.0±50.3 a
274.0±34.4 b
225.3±33.9 c
RESPIRATION9
Female
130.2±51.4 a
0.8203
272.9±35.9 b
0.9533
230.1±56.0 c
0.8553
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265
to baseline values. Conversely, coat color did impact the dog’s return to baseline when eye
266
surface temperature was examined with 12.5% black and 71.4% yellow dogs achieving baseline
267
values after their Cooling phase, as shown in Table 3 (P = 0.0406).
268
269 Table 3. Return to baseline1 rectal2, gastrointestinal3 (GI), thermal eye4, and thermal abdominal5
270 temperatures by coat color and sex.
271
272
273 ∗Notes a significant difference between groups
274 1Return to Baseline occurred when cooling temperature returned within 0.5◦F of the initial baseline temperature
275 reading measured 30 min prior to sunlight exposure (sunlight
276 2Rectal temperature was recorded by inserting a thermometer in 2cm rectally
277 3GI (gastrointestinal) temperature was recorded with an ingestible thermistor CorTemp 30 minutes prior to baseline
278 4Eye temperature was captured using thermography FLIR T400 at the left eye
279 5Abdominal temperature was captured using thermography FLIR T400 at the left caudal abdomen
280
281
Sex did not influence cooling as rectal temperatures returned to baseline in 22.2% and 16.7% of
282
female and male dogs respectively (P =1.00). Temperatures for the GI tract returned to baseline
283
in 55.6% of female and 33.3% of male dogs (P =0.6084).
284
Similarly, no effect of sex was observed for cooling of surface temperatures measured at
285
the caudal abdomen with 33.3% of female and 0% of male dogs returning to baseline values (P
286
= 0.6080). Eye surface temperature returned to baseline in 33.3% female and 50% of male dogs
287
achieving baseline values after their Cooling phase (P = 0.2286), as shown in Table 3.
288
289 Discussion
290
Black dogs did not demonstrate a difference in temperature following exposure to
291
direct sunlight when compared to yellow dogs for any of the parameters we examined,
VARIABLE
BLACK
YELLOW
P-VALUE
MALE
FEMALE
P-VALUE
RECTAL
12.5%
28.6%
0.5692
16.7%
22.2%
1.00
GI
50%
42.9%
1.00
33.3%
55.6%
0.6084
EYE
12.5%
71.4%
0.0406*
50%
33.3%
0.2286
ABDOMINAL
12.5%
28.6%
0.6080
0%
33.3%
0.6080
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13
292
including rectal thermometer using a standard medical-grade predictive digital thermometer,
293
GI temperature using an ingestible thermistor, eye surface temperature and abdominal
294
surface temperature using forward-looking infrared thermography, respiration or water
295
consumption. Contradictory to currently held beliefs, all dogs
experienced a similar rise
296
in rectal, GI, surface temperature, and respiration from the baseline to the sunlight
297
phase, with no difference shown between dark vs lighter coated dogs (P > 0.05) as shown
298
in Figures 3–5 and Table 1. Furthermore, no effect of sex was measured as both males
299
and females demonstrated similar responses to sunlight exposure and cooling based on
300
rectal, GI, eye surface, abdominal temperatures, and respiration rates (P > 0.05) shown
301
in Figures 6-8, and Table 2.
302
Contrary to the commonly held belief, our data demonstrated that black dogs did not
303
experience a greater heat gain than their yellow counterparts. Similarly, there was no
304
difference in the apparent thermoregulatory effect between dark and light dogs. This is
305
particularly noteworthy because of the relative short duration of the walk and the significant
306
temperature increase we observed in both dark and light-coated dogs. It is also interesting to
307
note that the 15-minute cooling period was inadequate for 80% of the dogs to achieve
308
baseline thermal status based on rectal measurements which are considered standard for
309
recording accurate temperature in animal species [16] .
310
Conversely, almost 50% of each group was able to return to a baseline values via
311
GI values after 15 minutes of cooling. This could be attributed to water consumption
312
during the cooling phase affecting the CorTemp capsule reading. [17] However, it is
313
important to note that all dogs did experience a significant decrease in their rectal, GI,
314
eye and abdominal temperatures, and respiration rates. Future work should include
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14
315
studies with a longer cooling period to determine that time frame necessary for
316
non-conditioned dogs to achieve baseline thermal status following thermal stress.
317
The data presented here are inconsistent with the previous study examining racing
318
greyhounds with larger proportions of dark coated dogs having higher rectal
319
temperatures after racing [5] . Key differences between this study and the prior study on
320
Greyhounds include controlled coat color (black or yellow vs. multiple light or dark
321
colors), tighter grouping of age and sex, and a controlled time period and consistent
322
environment. However, there were fewer dogs in our study compared to the study on
323
Greyhounds (16 vs. 229). Power calculations indicate that it would take more than 500 dogs
324
to adequately test this question using an alpha of 0.05 and 80% power. That number of dogs
325
is beyond our capacity. Furthermore, the greyhounds utilized in the previous study were
326
considerably more fit than the non-conditioned dogs used in our study. Fitness level can
327
impact thermal response as previously demonstrated in working canines [18, 19] and
328
should be examined as a controlled factor in future work.
329
Infrared thermal cameras have been widely used in livestock species to identify
330
changes in the surface temperature of the animals. These studies focused on areas that
331
had more skin exposure for more accurate data, such as the flank, eye, and facial region.
332
In our canine study, thermal images were captured inside a building to reduce effects
333
from wind, sun, and other environmental exposures. Both yellow and black dogs showed
334
similar changes in body surface temperatures which does not support the idea that coat
335
color is a potential risk factor for thermal stress. A comparison of skin surface
336
temperature during exposure to sunlight in dogs is warranted. There were some
337
challenges associated with the capture of the thermal imaging. Although the baseline
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338
photos were captured with little difficulty, many of the dogs were hot following the
339
sunlight exposure and several were non-compliant in assuming the same posture. More
340
obedient/compliant dogs would prove better subjects for this nature of study.
341
In designing the study, we considered that if body temperature measurements
342
were similar between the dark and light coated dogs, perhaps dark coated dogs simply
343
undertook increased efforts of thermoregulation such as increased respiration (i.e.
344
panting) or increased water consumption. However, we found no difference in these
345
parameters between the dark and light coated dogs, suggesting that the effort they
346
expended to thermoregulation was also similar. A key limitation in our study is that we
347
did not record heart rate, which would be important in assessment of thermoregulatory
348
response. More sophisticated instrumentation and monitoring would be important in
349
further studies to determine if more subtle physiological changes were occurring with
350
thermoregulation.
351
Novel data produced by this work include an absence of significant difference in
352
body temperature between black or yellow coated dogs. The techniques utilized to assess
353
temperature, panting and water consumption are non-technical, readily available methods
354
for canine handlers or owners to assess thermal status of dogs in the field, and thus are
355
important to prevention of heat related injury. These data provide critical evidence to dispute
356
the theory that dark coat color is a risk factor for thermal stress which is reported across
357
several forums including veterinary textbooks and previously published articles [1-4].
358
In this experiment, dark and light-colored dogs exposed to the same environment
359
showed a similar heat gain and loss (mean peak rectal 40.31±0.37 ◦C and mean peak GI
360
temperatures 40.65±0.37 ◦C respectively). This study also showed that when these non-
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361
conditioned dogs reached rectal temperatures near 40.9 ◦C (105.62 ◦F), and
362
gastrointestinal temperatures near 42◦C (106.16 ◦F), 15 minutes of rest in a cool room
363
with water available for consumption is adequate to begin to decrease the temperature,
364
although a return to baseline values may not be achieved within that time frame. No
365
medical intervention or active cooling method was needed to decrease the dogs’
366
temperature and nor heat-related negative health impacts were noted by the veterinary
367
team on site, despite dogs reaching temperatures as high as 42°C (106.16 F).
368
369 Ethical Conflicts
370
The authors declare that they had no conflict of interest.
371 Acknowledgements
372 The authors would like to thank the undergraduate and graduate students of Southern Illinois
373 University for their participation in this research. The researchers would also like to
374 acknowledge SIT Service Dogs for contributing the use of their dogs for this project.
375 Funding
376
This study was partially supported by the USDA-ARS Biophotonics (Grant
#
58-6402-
377
3-018).
378
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