abstract - KSU

Animal Science Journal (2012)
doi: 10.1111/j.1740-0929.2011.00993.x
ORIGINAL ARTICLE
Regional and circadian variations of sweating
rate and body surface temperature in camels
(Camelus dromedarius)asj_993 1..6
Khalid A. ABDOUN, Emad M. SAMARA, Aly B. OKAB and Ahmed A. AL-HAIDARY
Department of Animal Production, College of Food and Agricultural Sciences, King Saud University, Riyadh,
Kingdom of Saudi Arabia
ABSTRACT
It was the aim of this study to investigate the regional variations in surface temperature and sweating rate and to visualize
body thermal windows responsible for the dissipation of excess body heat in dromedary camels. This study was conducted
on five dromedary camels with mean body weight of 450 20.5 kg and 2 years of age. Sweating rate, skin and body
surface temperature showed significant (P < 0.001) circadian variation together with the variation in ambient temperature.
However, daily mean values of sweating rate, skin and body surface temperature measured on seven regions of the camel
body did not significantly differ. The variation in body surface temperature compared to the variation in skin temperature
was higher in the hump compared to the axillary and flank regions, indicating the significance of camel’s fur in protecting
the skin from daily variation in ambient temperature. Infrared thermography revealed that flank and axillary regions had
lower thermal gradients at higher ambient temperature (T a) and higher thermal gradients at lower T a, which might indicate
the working of flank and axillary regions as thermal windows dissipating heat during the night. Sweating rate showed
moderate correlation to skin and body surface temperatures, which might indicate their working as potential thermal
drivers of sweating in camels.
Key words: camel, infrared thermography, surface temperature, sweating rate, thermal window.
INTRODUCTION
In camels, sweat glands are distributed over nearly the
entire body except the lips, external nares and perianal
region (Lee & Schmidt-Nielsen 1962; Taha & Abdalla
1980). Several studies have shown a regional anatomical
difference in sweat gland density of relative species.
The guanaco showed higher densities of sweat glands
around the shoulder, lower part of the upper limb and
lower flank (Morrison 1966; de Lamo et al. 2001).
However, no difference in distribution or number of
sweat glands was found in samples taken from both
genders of guanaco at different times of the year. It has
been demonstrated that the axillary and flank regions
which are covered with very short and sparse pelage
are potentially more effective in evaporative heat dissipation
in guanaco (Morrison 1966).
The major transport mechanism for controlling heat
loss in camels seems to be the convective mechanism
of cutaneous blood flow (Al-Haidary 2006). Exposure
of camels to high ambient temperature (T a) would lead
to an increase in cutaneous blood flow due to peripheral
vasodilatation. Thereby, blood is shifted all over
camel’s body to create a thermal gradient between the
body and the external environment. Surface temperature
is normally used as a reflex index of body thermal
gradient (Curtis 1983). Local superficial venous circulation
is the main source of surface temperature
(Cameron et al. 2004). Vasomotor tone of peripheral
blood vessels in specialized heat exchanger regions
depends on the surrounding T a (Tattersall et al. 2009;
Weissenbock et al. 2010).
Controlling surface temperature is an important
mechanism in temperature regulation of homeotherms
(Phillips & Heath 1992). The major mechanism
of sensible heat loss is cutaneous vasodilatation
in specialized body regions which serves as a heat
Correspondence: Khalid A. Abdoun, Department of Animal
Production, College of Food and Agriculture Sciences, King
Saud University, PO Box 2460, Riyadh 11451, Kingdom
of Saudi Arabia. (Email: abdounn@yahoo.com; kabdoun@
ksu.edu.sa)
Received 20 June 2011; accepted for publication 26 September
2011.
© 2012 The Authors
Animal Science Journal © 2012 Japanese Society of Animal Science

2 K. A. ABDOUN et al.
exchanger with the environment. Such specialized
regions are characterized by high surface-to-volume
ratio, absence of fur, dense network of blood vessels
and the presence of arteriovenous anastomoses
(Wright 1984; Romanovsky et al. 2002; Mauck et al.
2003). The term ‘thermal window’ has been applied
to describe these regions (Williams 1990; Klir & Heath
1992). Later, the term ‘thermal window’ has referred
to any surface area of the body that is responsible
for efficient heat exchange (Sumbera et al. 2007).
Recently, thermal window has been defined as a
restricted surface area which is visible as a hot spot in
a thermal vision and differs by more than 5 o C from its
adjacent regions (Weissenbock et al. 2010).
The thermal camera is considered a state-of-theart
device. It absorbs infrared radiation and generates
images based on the amount of heat generated rather
than reflected (Eddy et al. 2001; Mazur & Eugeniusz-
Herbut 2006). Infrared thermography (IRT) has been
successfully used to visualize body thermal windows
on animal surfaces (Mauck et al. 2003; Tattersall et al.
2009; Weissenbock et al. 2010). IRT may also have
merit for assessing welfare (Stewart et al. 2005), resulting
from changes in body surface temperature associated
with adaptation to microclimate changes
(Kimmel et al. 1992; Knizkova et al. 1996; 2002).
Exchanging body heat with the surrounding environment
through thermal windows is achieved by
modifying blood flow in these regions via controlling
vasomotor tone (Sumbera et al. 2007). The camel’s
skin has numerous arteriovenous anastomoses which
could facilitate heat dissipation via high cutanoeus
blood flow. However, it is still questionable which
regions of the camel’s body are engaged in dissipation
of excess body heat. Therefore, this study was designed
to investigate the regional variations in surface temperature
and sweating rate and to visualize body
thermal windows responsible for the dissipation of
excess body heat in dromedary camels.
MATERIALS AND METHODS
This study was conducted during the summer season at the
experimental station of the Animal Production Department,
College of Food and Agricultural Sciences, King Saud University,
Riyadh region, Kingdom of Saudi Arabia. Five dromedary
camels of native breed (Majaheem) with mean body
weight of 450 20.5 kg and 2 years of age, were used in this
study. Animals were housed individually in shaded pens, fed
twice a day at 07.00 and 16.00 hours and had free access to
clean tap water.
Ambient temperature (T a), relative humidity (RH), sweating
rate (SR), skin temperature (T skin) and body surface temperatures
(T surface) were measured every 3 h for 2 successive
days. Ambient temperature and RH were recorded continuously
at 10 min intervals using two data loggers (HOBO
Pro Series data logger, Model H08-032-08, ONSET Co.,
Wareham, MA, USA) placed inside the pens. Thereafter,
temperature–humidity index (THI) was calculated according
to LPHSI (1990). Seven body regions (head, neck, shoulder,
axillaries, hump, flank and hip) were shaved and used as
sites for measurements of sweating rate and skin temperature.
Skin temperature was recorded using an infrared thermometer
(Traceable MiniIR Thermometer, Friendswood,
Texas, USA) with an accuracy of 1.0 o C and emissivity
of 0.95. The ratio of distance to the size of the spot being
measured was 1:1. Sweating rate was determined according
to the method proposed by Schleger & Turner (1965) and
modified by Pereira et al. (2010). Different body region
surface temperatures were recorded using a forward-looking
and automatically calibrating infrared camera (VisIR-Ti200
infrared vision camera, Thermoteknix Systems Ltd, Cambridge,
UK) placed perpendicular and approximately 50 cm
from the camels’ surfaces. This camera was equipped with a
25° lens, 1.3 Mpx visible camera, and LCD touch screen, and
had a 7.5–13 mm spectral range, and thermal accuracy of
2°C in addition to thermo-electrically cooling systems.
After capturing, thermograms were stored inside a 250 MB
internal memory, read out and analyzed using a special thermogram
analysis program (TherMonitor, Thermoteknix
Systems). For all thermograms, a rainbow color scheme was
chosen. Thermograms were analyzed by defining areas circumscribed
by hand with the software polygon function. The
software then gave back the average T surface within the defined
areas of the thermograms (Fig. 3).
The collected data were analyzed using Proc GLM; the
general linear models (GLM) procedure for analysis of variance
(ANOVA) of Statistical Analysis System (SAS 2003).
Completely randomized design with eight treatments (time
of the day) and five replicates (animals) was applied for
analysis. Factors that were used in the model included the
influence of study treatment (natural circadian variation of
T a), time of the day, body region, and their respective interactions.
Statistical means were compared using Duncan’s
multiple range test (DMRT). The overall level for statistical
significance was set at P < 0.05. All values are presented
as least square means standard error of the mean
(LSM SE).
RESULTS
The recorded T a and RH during this study showed
significant (P < 0.001) circadian variation with an
average value of 35.40 2.49°C and 10.95 1.99%,
respectively. The calculated average THI (29.50
1.70) indicated that animals had been exposed to
severe heat stress throughout the study (LPHSI 1990).
Ambient temperature and THI exhibited a circadian
rhythm (Fig. 1) with minimum values recorded early
in the morning (06.00 hour), and then gradually
increased to reach the maximum values at the middle
of the day (12.00–15.00 hours). Meanwhile, overall
mean of RH showed maximum values early in the
morning (06.00 hour) and minimum values at the
middle of the day (12.00–15.00 hours).
The regions of mean sweating rate, skin temperature
and body surface temperature showed significant
(P < 0.001) circadian variation together with the variation
in ambient temperature (Fig. 2). Sweating rate
showed a minimum value at 03.00 hour and a
maximum value at 15.00 hour. Skin and body surface
temperatures were minimum at 06.00 hour and
© 2012 The Authors
Animal Science Journal © 2012 Japanese Society of Animal Science
Animal Science Journal (2012)

CAMEL SWEATING AND BODY SURFACE TEMPERATURE 3
50
40
30
20
10
0
T a ( o C)
RH (%)
THI
0 3 6 9 12 15 18 21 24
Day time (hour)
Figure 1 Circadian rhythm of ambient temperature (T a),
relative humidity (RH) and temperature humidity index
(THI).
(°C)
50
45
40
35
30
25
20
SR (g·m -2·h -1 )
T skin (°C)
T surface (°C)
0 3 6 9 12 15 18 21
Day time (hour)
Figure 2 Circadian variations in skin temperature (T skin),
body surface temperature (T surface) and sweating rate (SR).
160
140
120
100
80
60
40
20
0
(g·m -2·h -1 )
maximum at 15.00 and 12.00 hours, respectively. The
correlation of sweating rate versus skin and body
surface temperatures revealed moderate correlation
with a coefficient of 0.60 and 0.57 (P < 0.001) for skin
and body surface temperatures, respectively.
Daily mean values of sweating rate, skin temperature
and body surface temperature measured on seven
regions of the camel’s body did not differ significantly
(Table 1). However, daily average variation in body
surface temperature (10.01 1.56 o C) was significantly
(P < 0.001) higher than the variation in skin
temperature (2.92 0.37 o C). Circadian variation in
body surface temperature (Fig. 3) was greatest in the
hump region (18.8 o C) and lowest in the axillary and
Table 1 Regional variation in average daily skin
temperature, body surface temperature and sweating rate
Regions SR T skin T surface
(g·m -2·h-1 ) ( o C) ( o C)
Head 82.21 10.49 35.68 0.13 34.38 0.56
Neck 84.98 11.17 35.28 0.19 34.28 0.55
Shoulder 89.50 11.35 35.33 0.22 34.32 0.57
Axillary 83.38 10.89 35.11 0.20 34.74 0.45
Hump 85.08 12.09 35.70 0.31 34.41 1.16
Flank 86.56 11.72 35.50 0.37 35.68 0.41
Hip 83.81 10.15 35.93 0.24 34.99 0.64
SR, sweating rate; T skin, skin temperature; T surface, body surface
temperature.
Table 2 Regional correlation of skin temperature versus
body surface temperature
Region
Correlation
P-value
coefficient
Head 0.35 0.049
Neck 0.55 0.001
Shoulder 0.71 < 0.001
Axillaries 0.51 0.003
Hump 0.85 < 0.001
Flank 0.22 0.238
Hip 0.76 < 0.001
27.5∞C
46.3∞C
33.8∞C
32.2∞C
39.6∞C
39.1∞C
6:00 am (T a = 25.12∞C)
12:00 am (T a = 45.40∞C)
Figure 3
Variation in body surface temperature at different ambient temperatures (T a).
Animal Science Journal (2012)
© 2012 The Authors
Animal Science Journal © 2012 Japanese Society of Animal Science

4 K. A. ABDOUN et al.
10
(a)
10
(b)
5
5
T s
- T a
(°C)
0
-5
T s
- T a (°C)
0
-5
-10
-10
20 25 30 35 40 45 50 20 25 30 35 40 45 50
T a
(°C)
T a (°C)
10 (c)
10
(d)
5
5
T s - T a
(°C)
0
-5
T s
- T a
(°C)
0
-5
-10
-10
20 25 30 35 40 45 50
T a
(°C)
20 25 30 35 40 45 50
T a
(°C)
10 (e)
10 (f)
5
5
T s
- T a
(°C)
0
-5
T s
- T a
(°C)
0
-5
-10
-10
20 25 30 35 40 45 50 20 25 30 35 40 45 50
T a
(°C)
T a
(°C)
10
(g)
10 (h)
5
5
T s
- T a
(°C)
0
-5
T s
- T a
(°C)
0
-5
-10
-10
20 25 30 35 40 45 50
T a
(°C)
20 25 30 35 40 45 50
T a
(°C)
Figure 4 Regional variation in thermal gradient between camel’s body surface and ambient temperatures (a = head,
b = neck, c = shoulder, d = axillary, e = flank, f = hip, g = hump, h = mean).
flank regions (6.9 and 5.8 o C, respectively). However,
daily variation in thermal gradient between camel’s
body surface and the surrounding environment was
lowest in the hump region and highest in the flank
and axillary regions (Fig. 4).
Body surface temperature showed significant correlation
with skin temperature in most of the studied
regions with an average correlation coefficient of 0.69
(P < 0.001). The highest correlation coefficient was
calculated for the hump and hip regions (Table 2).
However, body surface temperature was found to be
higher than skin temperature at high ambient temperatures
and lower than skin temperatures at low
ambient temperatures (Fig. 2).
© 2012 The Authors
Animal Science Journal © 2012 Japanese Society of Animal Science
Animal Science Journal (2012)

CAMEL SWEATING AND BODY SURFACE TEMPERATURE 5
DISCUSSION
This study was designed to investigate the regional
variation in body surface temperature and sweating
rate, in addition to the effect of natural daily circadian
variation of T a on body surface temperature and sweating
rate.
The results of the present study confirmed the existence
of a T a circadian rhythm during the study period
with a minimum T a (25.12 o C) observed early in the
morning and maximum T a (45.4 o C) observed at the
middle of the day, which produced concomitant
changes in body surface and skin temperatures and
sweating rate (Figs 1,2). This could be attributed to the
dependence of vasomotor tone of peripheral blood
vessels and the consequent skin blood flow on the
surrounding T a (Tattersall et al. 2009; Weissenbock
et al. 2010). However, the average daily surface and
skin temperatures and sweating rate did not show
significant regional variation (Table 1), which could be
due to the reported distribution of sweat glands over
nearly all body regions in camels (Taha & Abdalla
1980).
The daily average variation in body T surface was higher
than the variation in T skin, confirming that body T surface
is affected mainly by the variation in T a, while T skin is
regulated by vasomotor control (Curtis 1983). Further,
it has been demonstrated that T skin in the trunk region
of ox does not change very much at different T a
(Whittow 1962). The variation in body T surface (Fig. 3)
compared to T skin was higher in the hump compared to
the axillary and flank regions, indicating the significance
of camel’s fur in protecting the skin from the
daily variation in T a. This study has also discussed
the possible use of body T surface measured by infrared
thermographic technique as a representative of T skin.
Although, body T surface showed significant correlation
with T skin (r = 0.69), the body T surface showed high circadian
variation compared to the relatively stable T skin.
Therefore, body T surface could not be used as a representative
of T skin.
It is still unclear which regions of the camel’s body
function as the main avenues for the dissipation of
excess body heat. Therefore, infrared vision was taken
every 3 h throughout the day, and the daily variation
in thermal gradient between camel body surface and
the surrounding environment was been monitored
during the present study. The thermal vision (Fig. 3)
showed that body surface temperature was higher at
high T a and lower at low T a. However, the variation in
the body T surface was lowest in the flank and axillary
regions. Moreover, variation in thermal gradient was
lowest in the hump region and highest in flank and
axillary regions (Fig. 4). The flank and axillary regions
showed lower thermal gradients at higher T a (during
the day) and higher thermal gradients at lower T a
(during the night), indicating continuous blood flow to
the naked skin in the flank and axillary regions. This
indicates that flank and axillary regions might work as
thermal windows dissipating heat during the night.
This observation supports the previous reports on
guanaco which demonstrated that axillay and flank
regions with very short and sparse pelage are potentially
more effective in heat dissipation (Morrison
1966). Furthermore, this observation confirms the
earlier report that heat gained during the hot day is
dissipated during the cool night as a water economy
mechanism in camels (Lee & Schmidt-Nielsen
1962).
Correlation of sweating rate versus skin and body
surface temperatures revealed moderate correlation
(r = 0.60 and 0.57, respectively). This indicates that
skin and body surface temperature might work as
potential thermal drivers of sweating in camels.
Similar results have been reported for lactating cows
(Berman 1971) and ox (Whittow 1962). However,
thermal modulation of sweating in camels needs
further, more-oriented research.
Conclusion
Skin and body surface temperatures and sweating rate
in dromedary camels showed circadian variation concomitant
to the circadian rhythm of ambient temperature.
However, no regional variation across the camel’s
body was detected for the daily average skin and body
surface temperatures and sweating rate. Thermal gradient
between the surrounding environment and body
surface was lowest at high ambient temperature and
highest at low ambient temperature at the flank and
axillary regions, which indicates the probable working
of these regions as thermal windows dissipating heat
during the night.
ACKNOWLEDGMENTS
This work has been supported by the National Plan for
Science and Technology (NPST) program by King Saud
University, project number 09-BIO 885–02.
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Animal Science Journal (2012)