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Thermoregulation in pronghorn antelope (Antilocapra americana Ord) in the summer

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Abstract

We have used thermistor/data logger assemblies to measure temperatures in the brain, carotid artery, jugular vein and abdominal cavity, and subcutaneously, in five pronghorn antelope over a summer in Wyoming. Globe and air temperature varied by up to approximately 50 degrees C daily during the summer and maximum solar radiation was approximately 900 W m(-2). Brain temperature (38.9+/-0.3 degrees C) was consistently approximately 0.2-0.5 degrees C higher than carotid blood temperature (38.6+/-0.3 degrees C), which was the same as abdominal temperature (38.8+/-0.4 degrees C). Jugular blood temperature (38.0+/-0.4 degrees C) varied, probably because of changes in Respiratory Evaporative Heat Loss (REHL), and was lower than other temperatures. Subcutaneous temperature (38.3+/-0.6 degrees C) varied, probably because of peripheral vasoactivity, but on average was similar to other temperatures. Carotid blood temperature had a circadian/nycthemeral rhythm weakly but significantly (r=0.634) linked to the time of sunrise, of amplitude 0.8+/-0.1 degrees C. There were daily variations of up to 2.3 degrees C in carotid body temperature in individual animals. An average range of carotid blood temperature of 3.1+/-0.4 degrees C over the study period was recorded for the group, which was significantly wider than the average variation in brain temperature (2.3+/-0.6 degrees C). Minimum carotid temperature (36.4+/-0.8 degrees C) was significantly lower than minimum brain temperature (37.7+/-0.5 degrees C), but maximum brain and carotid temperatures were similar. Brain temperature was kept relatively constant by a combination of warming at low carotid temperatures and cooling at high carotid temperatures and so varied less than carotid temperature. This regulation of brain temperature may be the origin of the amplitude of the average variation in carotid temperature found, and may confer a survival advantage.
2444
Introduction
Pronghorn antelope are the only surviving member of the
Antilocapridae, a unique artiodactyl family that first appeared
in the late Miocene between 23.9 and 32.5
·Mya (Hassanin and
Douzery, 2003). Neither a deer nor a true antelope, its closest
extant relative is the giraffe (Mitchell and Skinner, 2003). It was
first brought to the attention of science by Meriwether Lewis
and William Clark during their exploration of the newly
acquired Louisiana territory (Lewis and Clark, 1904). In the
early autumn of 1804 (September 14) Lewis wrote:
–– in my walk I Killed a Buck Goat of this Countrey, about
the hight of the Grown Deer, its body Shorter the Horns which
is not very hard forks
J
up one prong short the other round &
Sharp arched, – Verry actively made, has only one pair of hoofs
to each foot, his brains on the back of his head, his Nostrals
large, his eyes like a Sheep he is more like the Antilope or
Gazella of Africa than any other Species of Goat.
In the intervening 200 years very few studies of their
anatomy and physiology have been done. Perhaps the most
famous study is that of Lindstedt et al. (Lindstedt et al., 1991),
who investigated the capacity of pronghorns for aerobic
exercise. They found it to be remarkable, with a V
O
2 of
300
·ml·kg
–1
·min
–1
, the highest recorded so far for any
vertebrate except perhaps for hovering hummingbirds (Suarez
et al., 1991) and bats (Lindstedt et al., 1991). To support this
oxygen consumption Lindstedt et al. showed that, compared to
goats, pronghorn have a greater capacity for oxygen diffusion
across the lung, a greater capacity to deliver oxygen to muscles,
and a greater total volume of mitochondria in skeletal muscle
(Lindstedt et al., 1991). These results confirmed aspects of an
earlier study by McKean and Walker (McKean and Walker,
1974) who, also comparing pronghorns to goats (Capra
hircus), found that pronghorns have a greater heart
weight:body weight ratio and a lower airway resistance.
Dhindsa et al. (Dhindsa et al., 1974) found that pronghorn
blood was unremarkable compared to several species of deer,
while McKean and Walker (McKean and Walker, 1974) found
50% more haemoglobin, a higher haematocrit, and larger blood
volume compared to goats. From the data provided by Dhindsa
et al. (N=4) (Dhindsa et al., 1974) and from the eight individual
We have used thermistor/data logger assemblies to
measure temperatures in the brain, carotid artery, jugular
vein and abdominal cavity, and subcutaneously, in five
pronghorn antelope over a summer in Wyoming. Globe
and air temperature varied by up to ~50°C daily during the
summer and maximum solar radiation was ~900·W·m
–2
.
Brain temperature (38.9±0.3°C) was consistently
~0.2–0.5°C higher than carotid blood temperature
(38.6±0.3°C), which was the same as abdominal
temperature (38.8±0.4°C). Jugular blood temperature
(38.0±0.4°C) varied, probably because of changes in
Respiratory Evaporative Heat Loss (REHL), and was
lower than other temperatures. Subcutaneous temperature
(38.3±0.6°C) varied, probably because of peripheral
vasoactivity, but on average was similar to other
temperatures. Carotid blood temperature had a
circadian/nycthemeral rhythm weakly but significantly
(r=0.634) linked to the time of sunrise, of amplitude
0.8±0.1°C. There were daily variations of up to 2.3°C in
carotid body temperature in individual animals. An
average range of carotid blood temperature of 3.1±0.4°C
over the study period was recorded for the group, which
was significantly wider than the average variation in brain
temperature (2.3±0.6°C). Minimum carotid temperature
(36.4±0.8°C) was significantly lower than minimum brain
temperature (37.7±0.5°C), but maximum brain and carotid
temperatures were similar. Brain temperature was kept
relatively constant by a combination of warming at low
carotid temperatures and cooling at high carotid
temperatures and so varied less than carotid temperature.
This regulation of brain temperature may be the origin of
the amplitude of the average variation in carotid
temperature found, and may confer a survival advantage.
Key words: pronghorn, brain warming, thermoregulation.
Summary
The Journal of Experimental Biology 210, 2444-2452
Published by The Company of Biologists 2007
doi:10.1242/jeb.005587
Thermoregulation in pronghorn antelope (Antilocapra americana Ord) in the
summer
A. Lust
1
, A. Fuller
2
, S. K. Maloney
3
, D. Mitchell
2
and G. Mitchell
1,
*
1
Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA,
2
Department of
Physiology, University of the Witwatersrand, Johannesburg, South Africa and
3
Physiology, School of Biomedical and
Chemical Sciences, University of Western Australia, Perth, Australia
*Author for correspondence (e-mail: mitchg@uwyo.edu)
Accepted 16 May 2007
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2445Pronghorn thermoregulation
animals on which McKean and Walker based their report
(McKean and Walker, 1974), however, it is also clear that
pronghorns have very different blood indices compared to
those calculated from average data for nine different species of
southern African antelope (Rhodes, 1975). Pronghorns have
significantly higher haematocrit (44.5±3.4 vs 39.8±3.7%;
t=2.76), haemoglobin concentration (16.8±2.0 vs
13.4±1.4·g·dl
–1
; t=4.36), and red blood cell number (11.8±1.1
vs 6.9±1.610
12
·l
–1
; t=7.42), and significantly smaller red cells
(mean corpuscular volume, MCV=37.1±2.7 vs 60.9±14.2·fl;
t=4.76) containing a lower absolute amount of haemoglobin
(MCH=14.1±1.1 vs 20.7±5.1·pg; t=3.70) but with a higher
concentration of haemoglobin per cell (MCHC=38.8±3.1 vs
33.5±1.3%; t=4.34). All these attributes allow them to run at
100·km·h
–1
for 3–4·min (McCabe et al., 2004) and 65·km·h
–1
for 10·min (McKean and Walker, 1974). The anatomy of their
cranial vasculature has been described (Carlton and McKean,
1977) and it is similar to that in other artiodactyls, specifically
in that it has a well developed carotid rete-cavernous sinus
system, one of the functions of which is to cool arterial blood
destined for the brain (Maloney and Mitchell, 1997).
Two measurements of their body temperatures have been
reported. Average temperature “under the deep musculature of
the paralumbar fossa” was 40.7°C (range 36.2–42.2°C) in a
mature doe and 39.0°C (range 36.8–42.2°C) in a yearling doe
(Thorne, 1975). Both animals were semi-tame. Mean rectal
temperature was 40.8°C (range 38.5–43.3°C) in 41 wild, hand-
captured animals (Barrett and Chalmers, 1977).
We report here a further study of pronghorn physiology, with
an emphasis on thermoregulation, using techniques we have
developed for use in southern hemisphere animals (Fuller et al.,
2005). The climatic conditions in the northern hemisphere are
different to those of the southern hemisphere and
thermoregulatory challenges experienced by pronghorn could,
therefore, be expected to be different. The aims of the study
were to record body temperatures in free-living pronghorn, to
describe the thermoregulatory mechanisms used by pronghorn
during a 3-month period in the summer in Wyoming, and to
compare these with temperatures and mechanisms we have
found in a free-living, similar-sized, South African antelope
(springbok Antidorcas marsupialis) during a southern
hemisphere summer (Fuller et al., 2005). We show that
thermoregulatory patterns in pronghorn and springbok are
similar, but pronghorns also seem to have evolved a mechanism
for warming their brains, not seen in southern hemisphere
artiodactyls.
Materials and methods
This study was done at the Tom Thorne/Beth Williams
Wildlife Research Center at Sybille, southeastern Wyoming
(Lat. 41.7789°N, Long. –105.3394°W). The study lasted from
12 May 2005 to 11 August 2005.
Animals
Five adult pronghorn Antilocapra americana Ord (one male
and four females, body mass 40–50·kg) were captured by
darting (thiafentanil, 5
·mg; Wildlife Pharmaceuticals, Inc., Fort
Collins, CO, USA) at Warren Air Force Base, and transported
to the research center. Prior to the start of the study the animals
were kept in a small, holding enclosure for 3–4 weeks so they
could recover from transport and acclimate to the local
environment. For the duration of the experiment they were kept
in a 200·hectare enclosure with four other pronghorns where
they were free-living for the 3-month recording period. During
the study one of the females gave birth to twins.
Measurement of body temperatures
Temperatures were measured and recorded from five body
sites (brain, carotid artery, jugular vein, abdominal cavity and
subcutaneous) using small bead thermistors (GE Thermometrics
ABOE3-BR11KA 103K-L10). Data were stored on data loggers
(Onset, Pocasset, USA; XITC 32+34+36) connected to the
thermistors by a flexible coax cable (#83265, Belden,
Richmond, IN, USA), and able to record temperature between
34°C and 46°C, every 5·min, to an accuracy of 0.04°C. The
loggers were waxed (paraffin wax/Elyax, Mini-Mitter, Sunriver,
OR, USA) to make them waterproof and biologically inert.
After waxing the loggers weighed approximately 55·g and
had dimensions of 50·mm45·mm20·mm. Each of the
thermistor/logger assemblies was calibrated against a quartz
thermometer (Quat 100, Heraeus, Hanau, Germany).
Surgical procedures
At the time of surgery the animals were re-darted using
thiafentanil and anesthetized with isoflurane (Abbott Animal
Health, Abbot Park, IL, USA) administered via a face mask at
a concentration of 8% for induction and 1–2% for maintenance
(mean=3.9±2.1%) in oxygen. The effects of thiafentanil were
reversed with nalterzel (5·ml; Wildlife Pharmaceuticals, Inc.).
Using aseptic surgical techniques, thermistors were implanted
into the five body sites and the loggers were buried
subcutaneously nearby.
Brain
To measure brain temperature a thermistor was encased in a
rigid guide tube (cellulose acetate butyrate tubing: World
Precision Instruments, Savarola, FL, USA; o.d. 3.2·mm, i.d.
1.98
·mm, length 34·mm) and pushed through a 3.2·mm hole
drilled through the skull in the midline 12.5·mm anterior to the
suture between the frontal and parietal bones, so that the
thermistor in the tip of the guide tube was near the
hypothalamus. These coordinates were determined by prior
dissection and analysis of pronghorn heads. The guide tube was
attached to a head plate (22·mm15·mm9·mm, LWH),
which was fixed to the skull by two 6-gauge, 15·mm long, self-
tapping, stainless steel screws. No neurological sequelae arose
from this procedure.
Blood vessels
Thermistors in a blind-ended, thin-walled, polytetra -
fluorethylene (PTFE) tube approximately 100·mm long, made
from a catheter (o.d. 0.9
·mm; Straight Flush 4F Catheter,
Cordis, The Netherlands), were inserted into the carotid artery
and jugular vein about midway along the length of the neck in
a direction opposite to the direction of the flow of blood so that
the thermistor was detecting the temperature of free-flowing
blood. The site of insertion in the vessels was closed by a purse-
string suture using 4/0 nylon.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2446
Subcutaneous and abdominal measurements
Thermistors used to measure subcutaneous and abdominal
temperatures were encased in a wax cylinder 40·mm long and
5·mm in diameter. The abdominal thermistor was inserted into
the abdominal cavity at the paralumbar fossa using a trocar and
cannula, and the logger buried subcutaneously above the site of
insertion. This method resulted in consistent placement of the
thermistor tip in the abdomen within small intestine folds and
posterior to the rumen (confirmed at autopsy). The logger
assembly was placed subcutaneously in the paralumbar fossa on
the opposite side to the abdominal assembly.
All animals were given 5·ml dexamethasone (Vedco, St
Joseph, MO, USA) and 2·ml penicillin (GC Hanford Mfg. Co.,
Syracuse, NY, USA) intramuscularly at the start of surgery.
Baytril tablets (22.7·mg; Bayer HealthCare LLC, Shawnee
Mission, KS, USA) were placed in all surgical sites prior to
wound closure.
Climatic conditions
Weather conditions during the study were measured using a
15-channel HOBO weather station (Onset). Six variables were
measured: black globe temperature, ambient air temperature,
solar radiation, relative humidity, wind speed and wind
direction. Black globe temperature is an integral of air
temperature, solar radiation and wind speed, and is the best
measure of total heat load.
Data analysis
Temperature data were obtained from all loggers in three
animals and from three loggers in a fourth animal. Insufficient
data was collected from the fifth animal. We obtained
measurements for 6 days from one animal, 12 from another, 92
from a third and 97 from the fourth. Most data analysis was
based on the measurements obtained from the latter two
animals. The data were consolidated by pooling the 12 5·min-
interval data points obtained from each logger for each hour of
measurement to produce 24 average hourly temperatures for
each animal for each day. These hourly averages for the four
animals were, in turn, averaged to produce a mean hourly
temperature for them as a group. These averages could be
further pooled for all study days or component days of the study
period to provide a comprehensive overview of body
temperatures throughout the recording period. For example, a
second consolidation was to average daily means into a week,
to produce 14 separate weekly temperature profiles for each
body site over the study period. These 14 weekly periods were
used to establish correlations between the weather variables and
body temperatures in each week of the study period.
Similar consolidations were made for weather data using the
two data points recorded each hour for each of the variables.
Calculation of cerebral blood flow (CBF)
The amount of heat lost from the brain (or any other tissue)
by convection to blood flow can be calculated from the
convective heat loss equation:
W = BF specific heat ⫻⌬T
·,
where W (J·s
–1
·100·g
–1
) is watts of heat produced by 100·g brain
tissue and removed by the blood, BF (g
·s
–1
·100·g
–1
) in the case
A. Lust and others
of the brain is cerebral blood flow (CBF) per 100·g brain tissue,
specific heat (J·g
–1
·°C
–1
) is constant and assumed to be
3.6·J·g
–1
·°C
–1
for blood (Jessen, 2001), and T is the
temperature gradient (°C) between T
brain
and T
carotid
. W varies
with T
brain
, which we assumed to have a Q
10
of 2.3 (Yablonskiy
et al., 2000). In order to account for the effects of changes in
T
brain
on oxygen consumption and CBF this value for Q
10
was
used to calculate a correcting function to take into account
the Q
10
effect on brain heat production, and was
W=0.0448.e
(Tbrain/11.7)
. W was then calculated for each brain
temperature. Using this estimate of W at each brain temperature
and rearranging the equation, CBF was calculated from:
CBF = [0.0448.e
(Tbrain/11.7)
/ (3.6T)]60·,
with the units of CBF being g·100·g
–1
·min
–1
, which were
converted to ml·100·g
–1
·min
–1
by dividing by the density of
blood (1.055·g·ml
–1
). This equation was used to assess the
extent to which observed differences between the carotid and
brain temperatures we found in this study could be attributed to
increased or decreased removal of heat by CBF.
Results
Weather conditions
Over the study period daily mean black globe temperature
(T
globe
) was 22.5±5.3°C (± s.d.) with a lowest measured
temperature of –5.0°C and a highest 52.0°C. Minimum T
globe
occurred at ~06:00·h and maximum T
globe
at ~13:00·h each day.
Mean air temperature (T
air
) was 18.3±5.0°C with a range of
2.0°C to 37.8°C. Mean daily solar radiation was 256±34·W·m
–2
and maximum solar radiation was 870±71·W·m
–2
. Mean
photoperiod was 14·h, 45±24·min, with sunrise occurring at
05·h, 41±0.13·min and sunset at 20·h, 27±0.11·min. Wind speed
was 1.1±0.3·m·s
–1
. No rainfall was recorded.
Body temperatures
Mean temperatures
The mean temperatures for the different body locations are
shown in Table·1. These data were derived by pooling hourly
mean temperatures over the study period for each temperature
site in the four animals. On average brain temperature
(T
brain
=38.9±0.3°C) was significantly higher than carotid artery
blood temperature (T
carotid
=38.6±0.3°C; t=5.23) and jugular
vein temperature (T
jugular
=38.0±0.4; t=3.21). T
carotid
was also
significantly higher than T
jugular
(t=2.14) but not different from
abdominal temperature (T
abdominal
; t=0.71) or subcutaneous
temperature (T
subcut
; t=0.81). T
jugular
was lower than T
abdominal
(t=8.00). Subcutaneous temperatures showed the largest
Table·1. Weighted mean hourly temperatures at each of the
body sites in four animals
Temperature (°C)
T
carotid
T
brain
T
jugular
T
abdominal
T
subcut
Mean 38.6±0.3 38.9±0.3 38.0±0.4 38.8±0.4 38.3±0.6
Range 35.8–40.3 37.4–40.7 36.1–39.9 35.0–40.4 34.1–40.3
N 4902 4037 2935 4902 4779
Temperatures are means ± s.d.; N, number of measurements.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2447Pronghorn thermoregulation
difference between maximum and minimum temperature
(6.2°C) and as a result on average were similar to T
abdominal
(t=0.75), T
brain
(t=1.62) and T
abdominal
(t=1.25). T
abdominal
did not
differ from T
brain
(t=0.36).
Individual variation in temperatures
Table·2 summarizes the variation in carotid and brain
temperatures in each of the four animals over the study period.
The male pronghorn had a minimum carotid temperature 1.6°C
higher than the female average and a maximum T
carotid
1.0°C
higher than the female average. The male’s minimum brain
temperature was 0.9°C higher than the female average but its
maximum brain temperature was the same as the female
average. These differences suggest that the male regulated its
body temperatures in a higher range than did the female
pronghorn. The minimum T
carotid
for all four animals was
significantly less than the minimum T
brain
(P<0.05; t-test) and
the range of T
carotid
was significantly wider than the range of
T
brain
(P<0.05; t-test). Maximum T
carotid
and T
brain
were not
significantly different.
These conclusions are supported by a slightly different
analysis of T
abdominal
shown in Table·3. To obtain these data,
hourly means for each hour of each day were averaged.
Thereafter the minimum and maximum temperature for each
day for each animal was calculated. These data support the idea
that the male pronghorn regulated his body temperatures within
a narrower and higher range than did the females, although with
data on only one male we cannot draw firm conclusions on
gender differences.
Frequency distribution of T
carotid
, T
brain
and T
jugular
Arithmetical means of temperatures are not necessarily the
same as preferred or mode temperatures, which are the
physiological, ‘set-point’ temperatures. The three most
important temperatures from a thermoregulatory point of view
are T
brain
, T
carotid
and T
jugular
, indicative of hypothalamic
temperature, core body temperature and the capacity for
respiratory convective and evaporative heat loss (REHL),
respectively. To determine the ‘set point’ temperatures for T
brain
and T
carotid
, frequency distributions of these two temperatures
were constructed for each animal by pooling measurements
made for each of them into 0.1°C intervals, combining these
intervals for all four animals and plotting the frequency (%)
occurrence of each 0.1°C interval. These analyses, derived from
over 52·000 paired data points (mainly from two animals) for
Table·2. Individual variation in carotid and brain temperatures
T
carotid
(°C) T
brain
(°C)
Gender Minimum Maximum Max–min Minimum Maximum Max–min
F593 35.9 38.7 2.8 37.4 39.7 2.3
F594 36.4 39.8 3.4 37.6 40.7 3.1
F598 35.8 39.3 3.5 37.5 39.7 2.2
M595 37.6 40.3 2.7 38.4 40.1 1.7
Group mean ± s.d. 36.4±0.8 39.5±0.7 3.1±0.4 37.7±0.5 40.1±0.5 2.3±0.6
N=4; each animal had a single highest or lowest T
carotid
or T
brain
during the study period.
Table·3. Daily variation of T
abdominal
over the summer
Gender T
max
(°C) T
min
(°C) T
max
T
min
(°C)
F593 38.4±0.4 36.4±0.8 2.0±0.9
F594 39.3±0.3 38.1±0.3 1.2±0.4
F598 39.2± 0.4 37.0±0.7 2.3±0.7
M595 39.6±0.3 38.9±0.2 0.7±0.2
Group mean 39.1±0.5 37.6±1.1 1.6±0.7
Temperatures are means ± s.d.; N=207 days.
Fig.·1. Frequency of occurrence of 0.1°C intervals of (A) brain and
jugular temperatures and (B) carotid temperature. The brain
distribution is narrower and its mode temperature occurs to the right of
the carotid and jugular distributions. The frequency of occurrence of
jugular temperatures is to the left of the carotid distribution and is
characterized by a long tail. Values are means ± s.d. (see text for N).
0
5
10
15
20
25
A
T
jugular
T
brain
0
5
10
15
20
25
35.5 36.5 37.5 38.5 39.5
Temperature frequency (%)
B
Temperature range (°C)
40.5
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2448
T
brain
, T
jugular
and T
carotid
, are shown in Fig.·1A,B. For all
animals, T
carotid
varied from 35.8°C to 40.3°C. T
brain
frequency
distribution was narrower (37.4–40.7°C). Fig.·1 also shows the
position of the distribution of jugular temperatures in relation to
carotid and brain temperatures. T
jugular
is significantly left-
shifted to both (Table·1) and is characterized by a long tail.
Factors affecting body temperatures
T
globe
The weekly range and mean of T
globe
had no significant
influence on the weekly variation in T
carotid
. The
product–moment correlation between the weekly means of
T
globe
and the weekly ranges of T
carotid
was 0.104 (F=0.132) and
for the weekly ranges of T
globe
and the weekly ranges of T
carotid
it was 0.203 (F=0.516). However, mean T
carotid
(as opposed to
its range) was correlated with the mean (r=0.78, F=18.19) and
the range of T
globe
(r=0.916, F=62.56) found in each week over
the course of the summer (Fig.
·2).
Circadian/nychthemeral rhythm
Consecutive maximum and minimum T
carotid
occurred on
average 24.0±1.5·h and 23.8±1.2·h apart, respectively. Using
the method of Nelson et al. (Nelson et al., 1979), variations
(over a period of three consecutive but randomly selected days
in each month) in T
globe
, and T
carotid
over the same days, in each
of the four animals were analyzed for the occurrence of a
circadian rhythm and evidence for daily adaptive heterothermy.
This analysis showed that throughout the summer, maximum
T
globe
occurred around 13:00·h (13·h 24±30·min), coinciding
with maximum solar radiation (12:24±0:24·h), while T
carotid
peaked 7·h later between 18:00·h and 21:00·h (18:47±1:05·h).
The amplitude of the circadian change was 0.8±0.1°C (Fig.·3).
To determine if the circadian rhythm was adjusted by
photoperiod, the mean time of occurrence of maximum T
carotid
and minimum T
carotid
in each of the 14 weekly periods was
correlated with mean time of sunrise or sunset in each epoch.
This analysis showed that the time of minimum T
carotid
was
positively correlated with the time of sunrise (r=0.634) and
negatively with the time of sunset (r=0.726). The time of
A. Lust and others
maximum T
carotid
was not significantly correlated with either
sunrise (r=0.019) or sunset (r=0.139).
Subcutaneous temperature
T
subcut
follows T
globe
quite closely throughout a day (Fig.·4),
although at night it separates from T
globe
. To assess if peripheral
vasoactivity could be a factor contributing to this pattern, T
subcut
was compared to T
carotid
. Assuming that the pelage minimizes
radiant heating of the subcutaneous space, then when T
globe
is
low vasoconstriction will result in an increase in the difference
between T
subcut
and T
carotid
, and a decrease in the difference,
resulting from vasodilation, will occur when T
globe
is increasing.
Fig.·4 shows an analysis of the difference between T
subcut
and
T
carotid
plotted against time of day. At night (19:00·h to 05:00·h)
when T
globe
is falling, T
carotid
on average is 1.0°C warmer than
T
subcut
. During the day (05:00·h to 19:00·h) when T
globe
is
increasing, the two temperatures become similar, suggesting
vasodilation and increased flow of warm blood to the periphery
in a typical heat loss mechanism.
Respiratory evaporative heat loss
The occurrence of REHL in pronghorn can be estimated by
analysis of T
jugular
. If heat is being lost via the nasal mucosa then
T
jugular
will fall because the temperature of blood returning in
38.0
38.2
38.4
38.6
38.8
39.0
39.2
A
7/24/057/23/057/22/05
10
15
20
25
30
35
40
45
50
0:00 12:00 0:00 12:00 0:00 12:00
Time of day (h)
B
T
carotid
(°C)
T
globe
(°C)
38.4
38.5
38.6
38.7
38.8
r=0.78
r=0.916
Mean T
carotid
(°C)
T
globe
(°C)
5 10152025303540
Fig.·2. The weekly mean pronghorn carotid blood temperature plotted
against the weekly mean (red) black globe temperature and the weekly
range (blue) of black globe temperature. As mean and variability of
globe temperature increases and decreases over the summer, mean
pronghorn temperature tends to change in the same direction.
Fig.·3. (A) Circadian rhythms over 3 days for one animal (22–24 July
2005) shown by cosinor analysis (Nelson et al., 1979), which fits a
‘best fit’ cosine wave to the actual data if such a wave form exists. Raw
data are represented by the blue line and the best-fit curve is in pink.
(B) Changes in T
globe
over the same 3 days. Note that the time of
maximum T
globe
occurs about 7·h before the time of maximum T
carotid
.
In both A and B, actual data points (diamonds) and their corresponding
calculated points (squares) are shown.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2449Pronghorn thermoregulation
the nasal veins to the jugular vein will fall. Conversely when
REHL is reduced T
jugular
will increase.
The relationship between T
carotid
and T
jugular
is shown in
Fig.·5A. When T
carotid
is below 37.5°C T
jugular
is warmer than
T
carotid
by 0.5–1.0°C, suggesting that REHL is reduced at these
T
carotid
. As T
carotid
increases mean and minimum T
jugular
become
less than T
carotid
indicating an increase in REHL. At T
carotid
of
approximately 39.5°C T
jugular
falls sharply, suggesting an
increase in REHL to a level greater than it is at lower T
carotid
.
The overall trend of this relationship is that as T
carotid
increases
so does T
jugular
but at a slower rate with the net effect that the
two temperatures diverge.
T
brain
/T
carotid
relationship
The relationship between mean, maximum and minimum
T
brain
and T
carotid
(Fig.·5B), shows that T
brain
varies less than
T
carotid
over the range of T
carotid
of 35.8°C and 40.3°C. Three
phases of T
brain
can be identified: (i) when T
carotid
is less than
37.8°C, (ii) when T
carotid
is between 37.8 and 39.5°C and (iii)
when T
carotid
is greater than 39.5°C.
Fig.·6 shows these three phases of T
brain
plotted with T
jugular
against T
carotid
. At T
carotid
of 37.8°C or less, T
brain
is remarkably
constant and both T
brain
and T
jugular
are warmer than T
carotid
.
T
jugular
is approximately 0.5°C warmer and T
brain
can be up to
2.5 to 3.0°C warmer.
At T
carotid
of between 37.8°C and 39.5°C (which corresponds
to the preferred ‘set point’ temperature frequency range;
Fig.·1A,B) T
brain
approaches T
carotid
with T
brain
being 0.2 to 0.5°C
warmer than T
carotid
. T
jugular
in this phase falls below T
carotid
but
increases in parallel with T
brain
.
The third phase of T
brain
occurs at T
carotid
greater than 39.5°C.
This phase is characterized by a sharp decline in both T
brain
and
T
jugular
such that T
carotid
becomes 0.5°C warmer than T
brain
, which
is characteristic of selective brain cooling (SBC), and implies
that brain heat is being removed faster than it is being produced.
SBC constitutes a small part of the regulation of T
brain
. Its
onset [as defined by a mean T
brain
less than T
carotid
(IUPS
Thermal Commission, 1987)] occurs at a T
carotid
close to 39.5°C,
a T
carotid
that occurs infrequently (less than 10% of all recorded
T
carotid
in this study). However, brain temperatures lower than
T
carotid
can be detected at T
carotid
as low as 38.0°C (Fig.·5B),
implying that SBC occurs over a wider range of brain
temperatures. The regulation of T
brain
also depends on the
amount of convective heat loss by CBF. The relative
contributions of CBF and SBC to brain heat removal can be
estimated from the T
carotid
T
brain
gradients recorded during the
Fig.·4. (A) T
subcut
and T
globe
(means ± s.d.) from 2 animals in July over
24
·h with means derived from 12 temperatures per hour, showing
coincident changes during the day (pink) and the separation of
temperatures at night (black). (B) In the mornings and evenings the
difference between carotid and subcutaneous temperatures increases
suggesting vasoconstriction, but narrows at midday suggesting
vasodilation.
36.5
37.0
37.5
38.0
38.5
39.0
39.5
0
10
20
30
40
50
60
A
–1.0
–0.5
0
0.5
1.0
1.5
2.0
B
T
subcut
(°C)
T
carotid
T
subcut
(°C)
00:00 12:00 15:00 18:0003:00 06:00 09:00 21:00
Time of day (h)
T
globe
(°C)
00:00 12:00 15:00 18:0003:00 06:00 09:00 21:00
Fig.·5. (A) Minimum and maximum (blue) and mean (red) T
jugular
and
(B) minimum and maximum (light blue) and mean (dark blue) T
brain
plotted against T
carotid
. At T
carotid
below ~38°C brain temperature stays
constant; between 38°C and ~39.5°C brain and carotid temperatures
approach each other as CBF increases and SBC begins. Above 39.5°C
typical SBC is evident. At carotid temperatures below ~37°C all three
jugular temperatures are above carotid temperature, but at higher
carotid temperatures mean and minimum jugular temperatures become
cooler reflecting an increase in REHL. Values are means ± s.d. but note
that error bars disappear from the mean jugular trace at low T
carotid
because data from only two animals could be matched to corresponding
data points for T
carotid
.
35
36
37
38
39
40
41
A
35
36
37
38
39
40
41
35 36 37 38
B
T
jugular
(°C)T
brain
(°C)
T
carotid
(°C)
39 40 41
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2450
study. If CBF is able to remove all brain heat then all the
temperature gradients between T
carotid
and T
brain
measured
should be accounted for by variations in CBF between the
minimum (~20·ml·100·g
–1
·min
–1
) (Heckman, 2001) and the
maximum (~80·ml·100·g
–1
·min
–1
) (Purves, 1972) possible.
Using the modified convection equation to calculate CBF, Fig.·7
shows the results of an analysis of this possibility and it is clear
that many of the measured gradients require explanations other
than changes in CBF: gradients of less than 0.2°C (Fig.·7A)
would require CBF above the assumed maximum and those
greater than 1°C (Fig.·7C) would require CBF below values
necessary to provide oxygen and glucose for brain metabolism.
Discussion
Only two previous studies have been done on pronghorn body
temperatures, with neither of these taking measurements
throughout a day or over a long period of time. The data reported
here are extensive and were obtained from five different body
sites in four animals, allowing some interpretation of the
thermoregulatory mechanisms used generally by pronghorn in
a Wyoming summer.
The pronghorns were exposed to weather conditions typical
of a hot and arid environment, characterized by large variations
in ambient temperature. They are dissimilar to southern African
climatic conditions. In the southern hemisphere summer days
are longer, wind speed lower and, while mean globe and air
temperatures are similar, in Wyoming the variation in globe and
air temperatures is 2–3-fold higher. Despite these conditions our
data show that the pronghorns in our study were able to maintain
a remarkably constant body temperature (38.6±0.3°C) over a
period of 3 months. These temperatures are lower than those
reported previously (Thorne, 1975; Barrett and Chalmers,
1977), and lower than those recorded in springbok in the
southern hemisphere summer (39.5±0.1) (Fuller et al., 2005). In
the former studies (Thorne, 1975; Barrett and Chalmers, 1977)
the difference can be attributed to the method of measurement
and the fact that the animals in those studies were subjected to
stress, while in ours they were free-living and able to use the
A. Lust and others
full array of thermoregulatory mechanisms available to them
from behavioral to physiological.
We did not make formal observations of behavior nor
correlate behavior with body temperature. However it was
obvious that pronghorn used the landscape, for example, to
avoid excess solar radiation (midday) and exposed themselves
to solar radiation in the mornings and evenings. It can also be
inferred that they used typical thermoregulatory mechanisms
associated with homeothermy, such as peripheral vasoactivity
(Fig.
·3) and REHL (Fig.·5). The mechanisms underlying REHL
depend on an adequate surface area for heat loss. We analyzed
the anatomy of the pronghorn nasal cavity and found that the
turbinate bones are scrolled, the length of the nasal cavity is
short (approximately 20·cm in the four animals in this study)
and the nasal mucosa surface area was 14.4·cm
2
for each cm of
length. Total surface area was 280·cm
2
, and this surface area is
similar to that in similar sized antelope (Kamau, 1992). During
REHL cardiac output is redistributed to the head, anastomotic
channels are opened between nasal mucosal arteries and veins
to enlarge the surface area for cooling, respiratory rate increases,
and finally, but not necessarily, there is panting (Maloney and
Mitchell, 1997). Our data provide some evidence that the same
mechanisms function in pronghorn.
Our data also reveal, however, that individual pronghorn
show a much greater variation in body temperatures than has
been found in southern hemisphere artiodactyls. Mean T
abdominal
was almost 1°C lower than it is in springbok and the difference
between maximum and minimum T
abdominal
of 5.4°C was
fivefold greater than that reported in springbok (Fuller et al.,
2005). There was a degree of heterothermy of more than 2.0°C
in a day in one animal and it seems that the females in the group
35
36
37
38
39
40
41
T
brain
and T
jugular
(°C)
35 36 37 38
T
carotid
(°C)
39 40 41
Fig.·6. Mean jugular (T
jugular
; red) and brain temperatures (T
brain
; blue)
plotted against carotid temperature T
carotid
, with the three phases of
brain temperature demarcated (see text). T
jugular
and T
brain
change in
parallel as T
carotid
increases, and increase at a slower rate than T
carotid
,
showing that T
jugular
and T
brain
are linked.
0
20
40
60
80
100
120
140
160
180
200
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
AB
C
CBF (ml 100 g
–1
min
–1
)
T
brain
T
carotid
gradient (°C)
Fig.·7. Calculated CBFs for 130 brain minus carotid temperature
gradients (T
brain
T
carotid
). The gradients were calculated by obtaining a
mean T
carotid
for 0.1°C intervals of T
carotid
and subtracting that mean
value from the corresponding average T
brain
. (A) CBFs above the upper
maximum CBF (pink line) cannot be achieved and the gradients
associated with these CBFs are produced by SBC. (C) CBFs below the
minimum CBF (yellow line) are unable to provide adequate oxygen
and glucose to the brain (see text) and the gradients measured cannot
be the result of reduced CBF. They must result from a brain warming
mechanism. (B) Gradients between A and C can be produced by
changes in CBF alone but are likely to be the result of changes in both
CBF and SBC.
THE JOURNAL OF EXPERIMENTAL BIOLOGY
2451Pronghorn thermoregulation
varied more than the male, although as there was only a single
male this latter conclusion is speculative. The females had an
average daily variation in T
abdominal
of 1.8°C, which also is
higher than we have found in southern hemisphere artiodactyls.
We have previously attributed variation in body temperatures to
episodes of exercise or fever and a nycthemeral rhythm. Our
animals in this study were not subjected to exercise and data
that could be attributed to fever were excluded. They did show
a well-developed circadian rhythm linked to sunrise as it is in
southern hemisphere animals (Fuller et al., 2005) but its
amplitude was about 1°C, and can explain neither the wider
daily variation nor the much larger range of temperatures
(4.5°C) found over the study period.
A variation in mean body temperature that correlates with
variations in mean and range of T
globe
over the course of the
summer are suggestive of a longer term heterothermy that could
account for another 0.25°C of the variation over the study
period. The amplitude of this variation is larger than that found
in springbok (Fuller et al., 2005). T
carotid
does not appear to be
affected by changes in day length as in southern hemisphere
animals (Fuller et al., 2005), and T
globe
was not significantly
correlated with day length (r=0.14). The dissociation between
T
globe
and T
carotid
in pronghorn as revealed by this analysis
confirms the presence of a circadian rhythm, and suggests that
pronghorn, even if they allow their body temperature to
fluctuate over a summer, do not have a daily adaptive
heterothermic response to environmental heat load.
To account for the remaining variation and the much wider
range of temperatures found than we have reported for
springbok, we think that another possible contributor is a lower
variation in T
brain
than in T
carotid
. The maximal thermoregulatory
responses to body temperature changes and, therefore, the
smallest variation in body temperature occur when both T
brain
and T
core
were changed in the same direction (Jessen and
Feistkorn, 1984). In our study this association is shown by the
very high proportion of core body (carotid) temperatures that
were recorded within the temperature range of 38.1–39.0°C
(Fig.·1). Within this range changes in T
carotid
and T
brain
are
correlated significantly (Fig.
·6; r=0.979), resulting in maximal
thermoregulatory responses to temperature challenges, and
defence of body temperature.
Outside of this ‘set point’ range T
brain
was dissociated from
T
carotid
and as a result thermoregulatory responses should be
blunted. The dissociation is achieved by what appears to be a
unique combination of mechanisms that combine to regulate
T
brain
rather than T
body
. Three factors influence T
brain
: its
metabolism, the rate of blood flow through it, and the
temperature of the blood perfusing it. Of these only the latter
two can be controlled. Brain metabolic rate is related to its
temperature. CBF is controlled to some extent by nerves but
mostly by metabolic rate and the demands for glucose and
oxygen and, we think, for heat removal. The temperature of
cerebral blood can be altered by the carotid rete-cavernous sinus
system which exists in all artiodactyls including pronghorns
(Carlton and McKean, 1977).
We calculate that changes in CBF can account for the heat
removed from the brain and the gradient between T
brain
and
T
carotid
in the range of 0.2–1.0°C, i.e. those which exist at
preferred T
carotid
. This conclusion is conservative. Our estimates
are based on the assumption that T
carotid
is the temperature of
blood entering the brain. In fact internal carotid artery (post-rete)
blood is cooler than T
carotid
when SBC is occurring (Maloney et
al., 2007) so the curve shown in Fig.·7 is likely to be left shifted,
SBC will account for a larger proportion of the gradients below
0.8°C, and changes in CBF for a smaller proportion.
Nevertheless gradients smaller than 0.2°C and indeed negative
gradients (T
carotid
>T
brain
), which occur at T
carotid
>39.5°C, cannot
be explained by changes in CBF and must depend on the onset
of SBC. Gradients above 1°C (and some as high as 3°C), which
occur at T
carotid
less than ~38°C, similarly cannot be explained
by a reduction in CBF. They are not conspicuous in the southern
hemisphere artiodactyls we have studied and therefore are so far
unique to pronghorn. The only way they can be achieved is by
a brain warming mechanism. As T
jugular
is greater than T
carotid
at
these T
carotid
, it follows that REHL is reduced during this phase
of brain temperature regulation, but in addition there is the
possibility that warm blood leaving the brain is being re-
circulated past the cavernous sinus before entering the jugular
vein. Warming of blood entering the brain, rather than cooling
it as is the more usual function of the carotid sinus–cavernous
sinus system, will result. However no anatomical basis for this
sort of re-circulation has been described in any animal. A second
possibility is that glial cell metabolism is activated at low T
carotid
as it is in dolphins (Manger, 2006). Again, however, no
anatomical basis for this possibility has been described in any
artiodactyl.
Whatever the mechanism of brain warming, it, and SBC at
high T
carotid,
produces a relatively constant T
brain
over the whole
range of T
carotid
temperatures we recorded during this study
(Fig.·5). If T
brain
is kept constant then a consequence should be
blunted thermoregulatory responses. The result will be an
increase in variation in T
carotid
, until T
carotid
and/or T
abdominal
are
themselves sufficiently low or high to activate thermoregulatory
responses (Jessen and Feistkorn, 1984). This effect could be the
origin of the significantly lower minimum T
carotid
and T
abdominal
than T
brain
, and the long tail of T
carotid
shown in Fig.·1.
These data show that pronghorns are homeotherms that have
some typical thermoregulatory mechanisms found in southern
hemisphere artiodactyls. They also, and specifically females,
seem to have evolved some heterothermic characteristics that
have made them well adapted to an arid environment in which
ambient temperature can vary by over 50°C during the course
of a typical summer day. While some of the temperature
variations can be attributed to a well-developed circadian/
nycthemeral rhythm, and to a longer term, direct effect of
changes in T
globe
, our data also strongly suggest that there may
also be a contribution arising from divergence between T
brain
and T
carotid
. Our data show that at low body temperatures T
brain
is maintained by a warming mechanism. At high body
temperatures T
brain
is cooled by SBC as in southern hemisphere
artiodactyls. The relatively constant brain temperature that
results is likely to result in the conservation of water and energy
needed by pronghorn to survive in their typical habitat in the
summer, when daily temperature fluctuations are high and the
availability of water is low.
We are grateful to Dr Terry Kreeger, Will Schultz, Clint
Mathis and Kurt Apel at the Sybille Research Station for their
THE JOURNAL OF EXPERIMENTAL BIOLOGY
help with the capture and care of the pronghorn, to the
Wyoming Game and Fish Department for their support of this
project, to Mark Nijland for assistance with surgery, to Robyn
Hetem for help with the construction of the logger assemblies,
Joe Bobbitt and Steve Devries for building the weather station,
to Dr Z. Zhang for microscopy, and to the University of
Wyoming for funding this project.
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A. Lust and others2452
THE JOURNAL OF EXPERIMENTAL BIOLOGY
... Ruminants respond to warm environmental conditions with physiological mechanisms that increase heat loss through evaporation, conduction, convection, or radiation. Vasodilation and increased heart rate transfers warm blood from the core of the body to the body surface where heat can be dissipated in areas such as the nasal cavity, ears or legs , Lust et al. 2007). Sweating and increased panting allows for evaporative heat loss from the surfaces of the skin and the respiratory tract . ...
... ungulates have a carotid rete that brings cooler arterial blood to the brain during hyperthermia (Mitchell et al. 2002, Lust et al. 2007, Strauss et al. 2017. Pelage characteristics can also influence both heat loss from insulation , and heat absorption from solar radiation (Hetem et al. 2009). ...
... Animals will then enter the "survival zone" if the duration and intensity of warm ambient air temperatures continue to increase at which point these animals are prone to hyperthermia and heat shock which could be fatal . Evaluating core body temperature of an animal on the landscape could provide an indicator for when an animal is entering the tolerance and survival zones , Lust et al. 2007, Schmidt et al. 2020, but have yet to be used to evaluate the relationship between the animal and its environment. ...
Thesis
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This study used core body temperature of moose (Alces alces) to evaluate the relationship between moose and their thermal environment. A novel technique to record body temperature was developed by modifying a vaginal implant transmitter which collected continuous body temperature at 5-minute intervals from female moose for up to one year. Using the vaginal temperature loggers, seasonal patterns of daily mean and daily change in core body temperature were established, with higher daily mean body temperature and daily change in body temperature during the summer than during the winter. Furthermore, body temperature of wild moose was elevated 1hr after chemical immobilization (38.9 °C) but returned to baseline levels within 3hr (38.0 °C), whereas captive moose body temperature was not elevated 1hr post immobilization (37.9 °C). Body temperature in wild moose rose above baseline levels and remained elevated from 12 to 48hrs post capture when movement rates were also elevated, possibly as a result of renarcotization from Carfentanil citrate. Following the animal indicator concept, we used large changes in body temperature (≥1.25 °C in 24h; heat response day) to indicate days of physiological tolerance to thermal stressors. Core body temperature, heart rate, respiration rate, rate of heat loss from exhaled air, and skin temperature were measured in female moose during the warm season. Thermal tolerance correlated with high ambient air temperatures from the prior day. At midday, moose exhibited daily minima of body temperature, heart rate and skin temperature that coincided with daily maxima in respiration rate and the rate of heat lost through respiration. Rumen temperature sensors and GPS collars were used to evaluate how behavior influences changes in rumen temperature in moose. Rumen temperature declined with low to moderate movement rates (<318 m • 0.5 hr-1) associated with foraging in all habitats, while rumen temperature increased for quick movement rates (>318 m • 0.5 hr-1). Moose moved more during heat response days (85.9 m • 0.5 hr -1) than control days (75.4m • 0.5 hr -1). Thermal tolerance of moose depends on the intensity and duration of daily weather parameters and the ability of the animal to use physiological and behavioral responses to dissipate heat loads.
... In northern climates, continuous core body temperatures have been measured on free-ranging pronghorn (Antilocapra americana- Lust et al. 2007;Hébert et al. 2008), alpine ibex (Signer et al. 2011), and Svalbard reindeer (Rangifer tarandus platyrhynchus- Arnold et al. 2018). For moose (Alces alces), records of core body temperature historically have been limited to single measures of moose either under chemical immobilization Neumann et al. 2011;Evans et al. 2012;Barros et al. 2018) or tethered in stalls (Renecker and Hudson 1986a). ...
... Further research relating activity and core body temperature in moose is warranted. The frequency distribution of core body temperature is narrow for moose (Fig. 2), similar to that measured for pronghorn in a temperate climate (Lust et al. 2007;Hébert et al. 2008), and for blesbok (Damaliscus phillipsi) in Africa (Hetem et al. 2016). The frequency distribution of core body temperature in moose was narrower than that of Arabian oryx (Oryx leucoryx), which employs hyperthermia-induced heterothermy in response to high ambient temperatures, resulting in a large range of core body temperature (Hetem et al. 2010(Hetem et al. , 2016. ...
... Moose exhibited a daily rhythm in core body temperature similar to other ungulates (Figs. 3B and 4;Fuller et al. 2005;Lust et al. 2007;Hetem et al. 2010;Signer et al. 2011;Shrestha et al. 2012); daily maximum body temperature was attained in the late afternoon and evening, whereas daily minimum body temperature was achieved before noon. We also documented a seasonal shift in the time of day that minimum and maximum core body temperature occurred, which has also been documented in alpine ibex and Arabian sand gazelles (Gazella subgutturosa marica- Ostrowski and Williams 2006;Signer et al. 2011). ...
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Variation in core body temperature of mammals is a result of endogenous regulation of heat from metabolism and the environment, which is affected by body size and life history. We studied moose (Alces alces) in Alaska to examine the effects of endogenous and exogenous factors on core body temperature at seasonal and daily time scales. We used a modified vaginal implant transmitter to record core body temperature in adult female moose at 5-min intervals for up to 1 year. Core body temperature in moose showed a seasonal fluctuation, with a greater daily mean core body temperature during the summer (38.2°C, 95% CI = 38.1–38.3°C) than during the winter (37.7°C, 95% CI = 37.6–37.8°C). Daily change in core body temperature was greater in summer (0.92°C, 95% CI = 0.87–0.97°C) than in winter (0.58°C, 95% CI = 0.53–0.63°C). During winter, core body temperature was lower and more variable as body fat decreased among female moose. Ambient temperature and vapor pressure accounted for a large amount of the residual variation (0.06–0.09°C) in core body temperature after accounting for variation attributed to season and individual. Ambient temperature and solar radiation had the greatest effect on the residual variation (0.17–0.20°C) of daily change in core body temperature. Our study suggests that body temperature of adult female moose is influenced by body reserves within seasons and by environmental conditions within days. When studying northern cervids, the influence of season and body condition on daily patterns of body temperature should be considered when evaluating thermal stress.
... Wildlife can respond to changes in daily and seasonal temperature through a combination of physiological, behavioral, and biochemical responses (Cain et al. 2006, Barboza et al. 2009). Physiological responses such as sweating, changes in respiration rate, or changes in deep body temperature can be used to assess when ungulates become heat-or cold-stressed (Parker and Robbins 1984, Renecker and Hudson 1986, Ostrowski and Williams 2006, Lust et al. 2007. Measuring body temperature of wild and captive ungulates is challenging and previously used methods have their limitations. ...
... Rectal temperature has been recorded while animals are anesthetized or restrained, but cannot be recorded after release (Franzmann 1972, Parker and Robbins 1984, Renecker and Hudson 1986, Rostal et al. 2012, Brivio et al. 2015. Surgical implants into the abdominal cavity have gathered valuable data on body temperature; however, data must be transmitted constantly via radio transmission to a receiver (Sargeant et al. 1994), or data stored within the temperature logger must be retrieved by surgery, which can pose risks to animals' health and is difficult to do on large wild ungulates, or by euthanasia (Fuller et al. 2005, Lust et al. 2007, H ebert et al. 2008, Hetem et al. 2010, Shrestha et al. 2012. Ruminal transmitter units can record continuous body temperature and do not require surgery (Signer et al. 2010, Turbill et al. 2011), but diet-induced thermogenesis and drinking events influence rumen temperature (Lawler andWhite 2003, Crater andBarboza 2007). ...
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Measuring body temperature in free-ranging ungulates is challenging. We evaluated a vaginal implant transmitter (TVIT) modified to collect continuous body temperature of captive and wild female moose (Alces alces) in Alaska, USA. We deployed TVITs in 18 moose between 2014 and 2016. We manually removed the TVIT after 51–338 days of deployment and sampled vaginal bacterial flora to assess negative effects of TVIT retention. For comparison, we also sampled vaginal flora from moose that did not have a TVIT. Mean bacterial growth scores were greater for moose with a TVIT than representative vaginal swabs from moose without a TVIT. The TVIT adequately collected body temperature measurements; however, the TVIT design could be improved to fit young, nulliparous moose. TVITs can be easily deployed and removed, but are limited by battery life, can only be deployed in adult female moose, and may increase vaginal bacterial concentrations.
... In artiodactyls (e.g. antelopes, cattle, sheep and goats), anatomical investigations (Ask-Upmark, 1935;Daniel et al., 1953;Gillilan, 1974;Carlton and McKean, 1977;Frąckowiak et al., 2015;Kiełtyka-Kurc et al., 2015), including the identification of osteological correlates in extant and extinct artiodactyls (O'Brien, 2016), and physiological studies (Johnsen et al., 1987;Mitchell et al., 1997;Fuller et al., 1999b;Maloney et al., 2002;Lust et al., 2007;Hebert et al., 2008;Hetem et al., 2012;Strauss et al., 2016) have confirmed the presence of the rete and its functionality in virtually all of the extant terrestrial artiodactyls, with informative exceptions (Fig. 1). In the vast majority of terrestrial artiodactyls, the carotid rete is found in lieu of the internal carotid artery and serves as the main supply of oxygenated blood to the brain (Schummer et al., 1981;Wible, 1984;Frackowiak, 2006;O'Leary, 2010;O'Brien, 2015). ...
... Individual variability in sympathetic responses to the same stressor may contribute to an underlying plasticity in the control of selective brain cooling (Strauss et al., 2016). (4) 38.9 ± 0.2 0.4 Eland Tragelaphus oryx (1) 40.0 0.4 (Fuller et al., 1999b) Gemsbok Oryx gazella (4) 39.8 ± 0.4 0.4 Gemsbok Oryx gazella (4) 39.5 ± 0.9 0.9 (Strauss et al., 2016) Kudu Tragelaphus strepsiceros (4) 39.3 ± 0.7 0.5 Febrile, naturally (Hetem et al., 2008) Kudu Tragelaphus strepsiceros (4) 38.8 ± 0.1 0.2 Afebrile (Hetem et al., 2008) Arabian oryx Oryx leucoryx (4) 37.8 ± 0.1 1.4 (Hetem et al., 2012) Springbok Antidorcas marsupialis (2) 39.2 ± 0.2 0.5 Pronghorn Antilocapra americana (2) 39.5 0.5 (Lust et al., 2007) Blue wildebeest Connochaetes taurinus (6) ...
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Some mammals have the ability to lower their hypothalamic temperature below that of carotid arterial blood temperature, a process termed selective brain cooling. Although the requisite anatomical structure that facilitates this physiological process, the carotid rete, is present in members of the Cetartiodactyla, Felidae and Canidae, the carotid rete is particularly well developed in the artiodactyls, e.g. antelopes, cattle, sheep and goats. First described in the domestic cat, the seemingly obvious function initially attributed to selective brain cooling was that of protecting the brain from thermal damage. However, hyperthermia is not a prerequisite for selective brain cooling, and selective brain cooling can be exhibited at all times of the day, even when carotid arterial blood temperature is relatively low. More recently, it has been shown that selective brain cooling functions primarily as a water-conservation mechanism, allowing artiodactyls to save more than half of their daily water requirements. Here, we argue that the evolutionary success of the artiodactyls may, in part, be attributed to the evolution of the carotid rete and the resulting ability to conserve body water during past environmental conditions, and we suggest that this group of mammals may therefore have a selective advantage in the hotter and drier conditions associated with current anthropogenic climate change. A better understanding of how selective brain cooling provides physiological plasticity to mammals in changing environments will improve our ability to predict their responses and to implement appropriate conservation measures.
... Furthermore, we documented a decline in the difference in skin temperature between the ear artery and ear surface during the morning, which may indicate vasodilation which could increase heat loss from the extremities. In pronghorn (Antilocapra americana), a similar time of day curve was observed with a daily nadir around midday for the difference between carotid artery and subcutaneous temperatures (Lust et al., 2007). Swift increases in air temperature during the morning elicited a salivary stress response from moose in this study, implying that the time frame for the declining portion of the daily body temperature curve may be important. ...
Article
We tested the concept that moose (Alces alces) begin to show signs of thermal stress at ambient air temperatures as low as 14 °C. We determined the response of Alaskan female moose to environmental conditions from May through September by measuring core body temperature, heart rate, respiration rate, rate of heat loss from exhaled air, skin temperature, and fecal and salivary glucocorticoids. Seasonal and daily patterns in moose body temperature did not passively follow the same patterns as environmental variables. We used large changes in body temperature (≥1.25 °C in 24hr) to indicate days of physiological tolerance to thermal stressors. Thermal tolerance correlated with high ambient air temperatures from the prior day and with seasonal peaks in solar radiation (June), ambient air temperature and vapor pressure (July). At midday (12:00hr), moose exhibited daily minima of body temperature, heart rate and skin temperature (difference between the ear artery and pinna) that coincided with daily maxima in respiration rate and the rate of heat lost through respiration. Salivary cortisol measured in moose during the morning was positively related to the change in air temperature during the hour prior to sample collection, while fecal glucocorticoid levels increased with increasing solar radiation during the prior day. Our results suggest that free-ranging moose do not have a static threshold of ambient air temperature at which they become heat stressed during the warm season. In early summer, body temperature of moose is influenced by the interaction of ambient temperature during the prior day with the seasonal peak of solar radiation. In late summer, moose body temperature is influenced by the interaction between ambient temperature and vapor pressure. Thermal tolerance of moose depends on the intensity and duration of daily weather parameters and the ability of the animal to use physiological and behavioral responses to dissipate heat loads.
... Stored temperature data from loggers such as the iButton ® [108,109] and the Star-Oddi DST loggers [110] can be easily downloaded via USB, and the loggers re-programmed by the user. Furthermore, fine thermistor/data logger assemblies can be used to monitor and store temperature readings from small, defined sites, such as the hypothalamus or a specific artery, in long-term field studies [71,111] and laboratory settings [112,113]. Battery life sets the limit to how many times the loggers can be reused. ...
Article
In most endothermic homeotherms, core body temperature follows a circadian rhythm. This review focuses on the amplitude of the circadian rhythm of body temperature (CRT) because the amplitude of the CRT has received increasing attention in the last few years. First, we discuss the methodology that can be used to measure the CRT, and the methodology used to calculate the amplitude of the CRT. Then, we illustrate the effect of changes in the external and internal environments on the amplitude of the CRT. Quite interestingly, as illustrated in this paper, while the molecular and hormonal basis of the CRT is well understood, the control of the amplitude is not. We conclude that challenges in the capacity of the animal to thermoregulate, or to manage energy, can impact on the amplitude of the CRT.
... My veterinary surgeon and physiologist brother Graham Mitchell, who mastered the technique of implanting radiotemeters not just in large African mammals but in the foetuses of sheep and goats, which then delivered young with radiotelemeters implanted (Laburn et al., 1992), decamped to the University of Wyoming, Laramie. I went to help investigate pronghorns Antilocapra americana, the 'American antelopes' that are not antelopes, and which endure a swing of ambient temperature (−30°C to +40°C) bigger than that endured by any African mammal (Lust et al., 2007). We went to Saudi Arabia, where Arabian oryx Oryx leucoryx and sand gazelle Gazella subgutturosa marica live in a desert with temperatures already higher than any African desert will reach in the next century, even under the worst climate change scenarios. ...
... This coupling results in one of the most effective mechanisms of brain cooling recorded for terrestrial vertebrates (Caputa, 2004). Many functional and experimental studies confirm the rete's role in thermoregulatory physiology across aerobic exercise (Taylor and Lyman, 1972;Jessen, 1998) and while free-ranging (Jessen et al., 1994;Fuller et al., 1999;Maloney et al., 2002;Lust et al., 2007). The cooling effect on the brain, particularly the hypothalamus, delays panting and sweating, compounding the temperature decline with a reduction in evaporative water loss (Taylor, 1970;Taylor and Lyman, 1972;Robertshaw and Demi'el, 1983;Kuhnen, 1997;Aas-Hansen et al., 2000;Robertshaw, 2006). ...
... see Habitat -Habitat Characteristics/Description Physiology Bear 1967b; Bear et al. 1973b;Booren et al. 1973;Byers 2006;Cain III et al. 2006;Carsana et al. 1983;Clemens et al. 1987;Dhindsa et al. 1974;Hoffman 1989;Holz 1981;Larsen 1964bLarsen , 1965bLarsen , 1967bLust et al. 2007;Markham et al. 1980b;Martin et al. 1992;Maher 2000;Mitchell et al. 2009;O'Gara 2004c;Painter 2005;Pojar and Miller 1984;Pojar and Spraker 1986;Pojar and Wolfe 1982;Pond 1978;Popel et al. 1994;Seal and Hoskinson 1978;Tluczek et al. 2010;Turner and Hall 2009;Walker 1974;Weibel 1999a, b;Wesley et al. 1969Wesley et al. , 1970Wesley et al. , 1973Whisler andLindstedt 1982, 1983. -Energetics Hébert 2006; Hébert et al. 2008;Lindstedt et al. 1988Lindstedt et al. , 1991Miller and Byers 1991;Wesley 1971;Wesley et al. 1970Wesley et al. , 1973 -Iodine Markham et al. 1980b. ...
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Sözüer, Ö. (2019). BİYOKÜLTÜREL ÇEŞİTLİLİK UNSURU OLARAK, HONAMLI KEÇİ IRKI (Race of Honamlı Goat, As a Biocultural Divercity Item) (Unpublished master's thesis). Burdur/Mehmet Akif Ersoy Univercity. Retrieved May 9, 2019, from https://tez.yok.gov.tr/UlusalTezMerkezi/tezSorguSonucYeni.jsp, 2019 ABSTRACT Race of Honamlı Goat, As a Biocultural Divercity Item This study was conducted to show the ecological effects, cultural effects and phenotypic characteristics of the Honamlı goat breed, registered as a native breed in 2015 and to evaluate the consistency between the traditional ecological knowledgetransferred over generations and the results of statistical analysis. The material for this study was the registered Honamlı goat herds in the provinces of Antalya and Burdur, the Kermes oaks (Quercus coccifera) around the farms, with and without trunks, conducted through face to face interviews with herd owners and local and non–local people. For identification of the phenotypic characteristics of the Honamli breed of goat, hair colour, eye colour and the ear length of 869 goats were evaluated. A total of 90 oaks around the farms with an equal number of trunks that are browsed without pruning and over –browsed or non–browsed, as also in the form of the trunk-less shrubs cut by shepherds, were measured, for trunk length, total length and the leaf length of 5 leaves per tree. From the trunk the leaf length measured 28.4mm, total length, 374.6 cm, the leaf length of the non–trunked was 18.3 mm and the total length 99.2 cm. The trunk length was 178,73 cm. Through a semi-structured free-listing interview technique, native and non-native local people and herd owners were questioned. In these interviews, the questions concerned: the most common edible plants for the Honamlı goats in the region, the most commonly consumed animal meat in the region, and, how to understand the large amount of meat production. According to the results, the most salience elements of cultural importance were: piynar (the Kermes oak), goat meat eaten by residents and chicken meat by the non–local youngs andlonger body length locally called“ sallilik” of goats. The highest correlation between the phenotypic characteristics of the Honamlı goat breed was found between live weight and the body length, mentioned as sallilik (r=0,629). The difference between the ear lengths locally entitled was also statistically significant. As a result of this study, it was shown that the goat-forest relationship could not be explained ecologically through only defining the goat as a forest pest, and, it was also shown that extensive goat breeding is an environmentally friendly form of animal husbandry and goat might be accepted to be a product of forestry. Keywords: Biocultural Divercity, Honamlı Goat, Goat Meat, Kermes Oak (Quercus Coccifera) ÖZET Biyokültürel Çeşitlilik Unsuru Olarak, Honamlı Keçi Irkı Bu çalışma, 2015 yılında yerli ırk olarak tescil edilen Honamlı keçi ırkının ekolojik etkileri, kültürel etkileri ve fenotipik karekterlerini bilimsel olarak ortaya konması ve böylece kuşaktan kuşağa aktarılan geleneksel ekolojik bilginin, istatistiki analiz sonuçlarıyla arasındaki tutarlılığın değerlendirilebilmesi amacıyla yapılmıştır. Çalışmanın materyalini, Antalya ve Burdur il sınırlarındaki kayıtlı Honamlı keçi sürüleri, işletmelerin etrafında gövdeli ve gövdesiz Kermes meşeleri (Quercus coccifera), sürü sahipleri ve yörenin yerlisi olan ve olmayan yöre insanı ile yapılan bire bir görüşmeler oluşturmuştur. Honamlı keçi ırkının fenotipik karakterlerinin tanımlanması için farklı sürülerden 869 keçininvücut örtü rengi, göz rengi ve kulak uzunluğu gibi özellikleri değerlendirilmiştir. İşletmelerin etrafındaki, kesilmeden otlatılan eşit sayıda gövdeli ve aşırı otlatılan ya da az otlatılan, aynı zamanda çobanlar tarafından da kesilen gövdesiz çalı formundaki toplam 90 adet meşede, gövde boyu, toplam boy ve her ağaçtan 5’er yaprak boyu ölçülmüştür. Gövdeli meşelerde yaprak boyu 28,4mm, toplam boy 374,6cm, gövdesizlerde ise yaprak boyu 18,3mm, toplam boy ise 99,2cm olarak bulunmuştur. Gövdelilerin gövde boyu ise 178,73cm’dir. Yörenin yerlisi olan ve olmayan yöre insanına ve sürü sahiplerine yarı yapılandırılmış “freelisting–aklına gelen” görüşme tekniği uygulanmıştır. Bu görüşmelerde yörede Honamlı keçilerinin en çok yediği bitkiler, yörede eti en çok tüketilen hayvanlar ve yörede Honamlı keçilerinin et veriminin yüksekliğinin nasıl anlaşıldığı sorulmuştur. Buna göre kültürel belirginliği en çok öne çıkanöğeler sırasıyla piynar (Kermes Meşesi), yerelde keçi eti, gençlerde tavuk eti ve keçilerin sallılığı olarak bulunmuştur. Honamlı keçi ırkının fenotipik karakterleri ile ilgili olarak canlı ağırlık ile en yüksek korrelasyon, sallılık olarak ifade edilen vücut uzunluğu arasında bulunmuştur (r=0,629). Yöresel olarak isimnlendirilen kulak uzunlukları arasındaki fark da istatistiki olarak anlamlı bulunmuştur. Ayrıca çalışma sonucunda keçi ve orman ilişkisinin, ekolojik olarak keçinin sadece orman zararlısı olarak tanımlanmasıyla açıklanamayacağı ve ekstansif keçi yetiştiriciliğinin doğa dostu bir hayvancılık biçimi olduğu ve keçinin de bir orman ürünü olarak kabul edilebileceği ortaya konmuştur. Anahtar kelimeler: Biyokültürel Çeşitlilik, Honamlı Keçisi, Keçi Eti, Kermes Meşesi (Quercus Coccifera)
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Respiration rates of muscle mitochondria in flying hummingbirds range from 7 to 10 ml of O2 per cm3 of mitochondria per min, which is about 2 times higher than the range obtained in the locomotory muscles of mammals running at their maximum aerobic capacities (VO2max). Capillary volume density is higher in hummingbird flight muscles than in mammalian skeletal muscles. Mitochondria occupy approximately 35% of fiber volume in hummingbird flight muscles and cluster beneath the sarcolemmal membrane adjacent to capillaries to a greater extent than in mammalian muscles. Measurements of protein content, citrate synthase activity, and respiratory rates in vitro per unit mitochondrial volume reveal no significant differences between hummingbird and mammalian skeletal muscle mitochondria. However, inner membrane surface areas per unit mitochondrial volume [Sv(im,m)] are higher than those in mammalian muscle. We propose that both mitochondrial volume densities and Sv(im,m) are near their maximum theoretical limits in hummingbirds and that higher rates of mitochondrial respiration than those observed in mammals are achieved in vivo as a result of higher capacities for O2 delivery and substrate catabolism.
Book
Introduction.- The Skin as a Source of Temperature Signals.- The Inner Body as a Source of Temperature Signals.- The Neuronal Basis of Temperature Reception.- Heat Production and Heat Balance of the Body.- Physics of Heat Exchange with the Environment.- External and Internal Insulation.- The Temperature Field of the Body Core.- Behavioural Control of Heat Exchange with the Environment.- Autonomic Control of Dry Heat Loss from the Skin.- Autonomic Control of Evaporative Heat Loss.- Interaction of Various Body Temperatures in Control of Thermoregulatory Responses.- The Central Interface Between Afferent Temperature Signals and Efferent Drives.- Short-Term Temperature Regulation in Various Environments: Inputs and Responses.- Exercise in the Heat: the Ultimate Challenge.- Changes of Set-Point.- Adaptation to Cold.- Adaptation to Heat - Pathophysiology of Temperature Regulation.- References.- Subject Index.
Article
The origin, phylogeny, and evolution of modem giraffes (Giraffa camelopardalis) is obscure. We review here the literature and conclude that the proximate ancestors of modern giraffes probably evolved in southern central Europe about 8 million years ago (Mya). These ancestors appear to have arisen from the gelocid ancestral assemblage of 20–25 Mya via the family Palaeomerycidae. From the palaeomerycids arose the Antilocaprinae (Pronghorns) via the subfamily Dromomerycinae, and two subfamilies of giraffids, the Climacoceratidae and Canthumerycidae. The terminal genus of the Climacoceratid line was the now extinct massive giraffid Sivatherium sp. The Canthumerycids gave rise to the okapi and giraffes via the intermediate forms of Giraffokeryx, Palaeotragus sp. (of which the okapi is the extant form), Samotherium sp. and Bohlinia sp. All of which are extinct. Stimulated by climate change, progeny of Bohlinia entered China and north India, evolved into typical Giraffa species and became extinct there about 4 Mya. Similarly, following their preferred habitat, African Giraffa entered Africa via Ethiopia about 7 Mya. Here, seemingly unaffected by the climate changes occurring to the east and causing extinction of its Asian counterparts, Giraffa radiated into several sequential and coeval species culminating with the evolution of G. camelopardalis in East Africa from where it dispersed to its modern range. Fossils of G. camelopardalis appear about 1 Mya in East Africa.The underlying stimulus for Giraffa evolution seems to have been the vegetation change that began about 8 Mya, from the prevalent forest (C3) biome to a savannah/woodland/shrub (C4) biome. Giraffa's success as a genus is attributed to its great height and unique coat markings. Its height is a consequence of elongation of all seven cervical vertebrae and of the lower more than the upper limb bones. Advantages conferred by its height include protection from predation, increased vigilance, and in males sexual dominance and access to nutrients. Its coat colourings are highly hereditable and provide protection from predation by camouflage, especially in the young. As giraffe are unable to sweat and pant, the patches may also act as thermal windows and may have an important thermoregulatory function.
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Clinicochemical parameters for 106 free-ranging, adult pronghorns (Antilocapra americana) trapped in southeastern Alberta were obtained in 1973 and 1974. Mean calcium, magnesium, phosphorus, sodium, and potassium values were 11.62 g/dl, 2.46 g/dl, 6.42 g/dl, 167.01 mequiv./ℓ and 6.99 mequiv./ℓ, respectively. Values for serum enzymes displayed great variation and in many cases were extremely elevated; mean values for glutamic-oxaloacetic transaminase (EC 2.6.1.1), glutamic-pyruvic transaminase (EC 2.6.1.2), creatine phosphokinase (EC 2.7.3.2), and alkaline phosphatase (EC 3.1.3.1) were 251.45 Reitman–Frankel units (R.F.u.)/ml, 1820 R.F.u./ml, 432.09 IU/dl, and 4.63 King–Armstrong units (K.A.u.)/ml, respectively. Similarly, extensive variation in serum chemistry was observed for cholesterol, glucose, creatinine, and blood urea nitrogen with mean values of 42.97, 249.95, 11.60, and 42.82 mg/dl, respectively. Mean serum protein was 7.32 g/dl and the albumin: globulin ratio averaged 1.97; data on electrophoretic fractionation of serum proteins are presented. Significant (P < 0.05) differences in clinicochemical values were associated with year of sampling, age, and sex of animals, and duration of processing delay. Handling stress was believed to have a strong influence on observed clinicochemical values.
Article
Selective cooling of the brain during heat stress has been shown by others to be a method of temperature regulation for mammals having carotid retia. This study describes the macroscopic anatomy of the cranial circulation of elk, deer and pronghorn as it might pertain to the functioning of carotid retia and orbital retia as heat exchangers. Emphasis has been placed on describing the source of venous blood bathing these retia, for blood flow from these sources to the ophthalmic plexus and cavernous sinus will establish a temperature difference between arterial and venous blood, and influence the magnitude of this gradient. The pronghorn possesses a carotid rete with greater density and smaller calibre vessels overall and a more highly vascular orbital rete compared to the elk and the deer. These anatomical differences may indicate differences in efficiency of heat exchange in the retia. It is suggested that the orbital rete is anatomically in a position to moderate extremes of temperature by cooling arterial blood flowing to neural tissue of the eye and olfactory bulbs.
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The pronghorn antelope (Antilocapra americana) has an alleged top speed of 100 km h-1, second only to the cheetah (Acionyx jubatus) among land vertebrates, a possible response to predation in the exposed habitat of the North American prairie. Unlike cheetahs, however, pronghorn antelope are distance runners rather than sprinters, and can run 11 km in 10 min, an average speed of 65 km h-1. We measured maximum oxygen uptake in pronghorn antelope to distinguish between two potential explanations for this ability: either they have evolved a uniquely high muscular efficiency (low cost of transport) or they can supply oxygen to the muscles at unusually high levels. Because the cost of transport (energy per unit distance covered per unit body mass) varies as a predictable function of body mass among terrestrial vertebrates, we can calculate the predicted cost to maintain speeds of 65 and 100 km h-1 in an average 32-kg animal. The resulting range of predicted values, 3.2-5.1 ml O2 kg-1 s-1, far surpasses the predicted maximum aerobic capacity of a 32-kg mammal (1.5 ml O2 kg-1 s-1). We conclude that their performance is achieved by an extraordinary capacity to consume and process enough oxygen to support a predicted running speed greater than 20 ms-1 (70 km h-1), attained without unique respiratory-system structures.
Article
Pronghorn (ilocapra americana are probably the second fastest land mammal with a top speed of about 100 km/hr. Pronghorn are endurance runners as well as they have been observed running at an average speed of 65 km/hr for over 10 min. To determine if the pronghorn has become physiologically adapted for running a number of parameters which are thought to influence the delivery of 02uscle and the removal of respiratory and metabolic acids both in the pronghorn and in its unspecialized control, the domestic goat, were measured. Average values obtained are as follows: View Within ArticleIt is concluded that the pronghorn is physiologically adapted for running compared to goats of equal size.