| dc.description.abstract | In this study, thermal and metabolic adaptations
to heat and exercise have been investigated in the two
species during treadmill running at speeds between 0-
15 km.h-1 and on gradients between 0-70• An open
flow system was employed to measure oxygen consumption
while the animals ran at the different speeds and
gradients both while loaded and unloaded. A heat
balance evaluation while animals ran and while at rest
in a climatic chamber at ambient temperatures of 15-
400c was also ascertained. The following series of
experiments were carried out under controlled laboratory
conditions:
a) Energy expenditure during exercise;
b) Energy expenditure and heart rate during
exercise;
c) Energetic cost of carrying loads;
d) Thermoregulation during dehydration;
f) The role of the extremities in
thermoregulation.
The energy cost of running increased
proportionately with running speed. Regression lines
describing the relationship between metabolic rate and
-xxirunning
speed (Vr) for the two species are
given below :-
Donkeys 0.94 + 0.41 Vf (r 0.89, n 60)
Camels = 0.62 + 0.32 Vf (r = 0.91, n = 20)
where metabolic rate is in W.kg-1 (assuming
20.1 J.ml -102) ,V . . -1 f 1S speed 1n km.h ,
n is the number of observations in each experiment and
r is the regression coefficient.
It was observed that the camel and the_.donkey consumed
less energy than would be predicted on the basis of
their body weight at anyone given speed
between 0-15 km.h-1. The minimum net costs of
transport were 1.7 J.kg-1.m-1 and
1.3J.kg-1m-1 for the donkey and camel
respectively. Similarly; the 'optimal' (speed at
which the mechanical energy changes of the centre of
mass are minimised by pendulum-like transfers between
the kinetic and potential energy of the centre of
mass) walking speeds were about 4 km.h-1 and
6 km.h-1 for the donkey and camel respectively.
There was a proportionate increase in the heart
rate as the running speed increased in both species.
A relationship between the heart rate and the energy
expenditure was described by the following equations:
Heart rate i) Donkeys 6.56 + 23.80H
(r = 0.82, n = 60)
ii) Camels 25.61 + 14.99H
(r = 0.87, n = 20)
where heart rate is in beats. min-1 and H is metabolic
rate in W. kg-1,n is the number of observations in each
experiment and r is the regression coefficient.
The mechanical efficiency of performing external
work while carrying loads ranging between 20-80 kg at
speeds between 2-6 km.h-1 and at treadmill gradients
of 30, 50 and 70 was 22%.
Efficiency ranged between 12-35% depending on the
walking speed and load being carried.
The regulation of body temperature as well as
pulmocutaneous evaporation at rest and during exercise
was investigated. It was observed that the donkey and
camel allowed their body temperatures to rise during
treadmill exercise. The degree of body temperature rise was
dependent on the speed and duration of exercise. At
speeds of up to 6 km.h-1, however, the animals were
able to regulate their body temperatures at levels
slightly higher than the resting. At speeds higher
than 6 km.h-1 body temperature tended to keep on
rising as long as the exercise lasted. At speeds
of 10 km.h-1 and 15 km.h-1, heat storage
accounted for 57% and 56% of the total heat production
in the donkey, respectively. In the camel at the same
speeds, heat storage was 77% and 87% of the total heat
production, respectively. Total evaporative heat loss
(TEHL) during exercise increased with increasing
- -
speed. This was particularly so in the donkey where
TEHL accounted for 35% of the total heat production at
speeds of 10 km.h -1. In the camel, however, l.t
was observed that percentage TEHL tended to decline as
speed increased accounting for only 19% of the total
heat productlo.n at a speed of 10 km.h -1..
Following exposure to high ambient temperatures in
the climatic chamber, cutaneous evaporative heat loss
(CEHL) was the major route of heat dissipation in
both species. After exposing the animals to an ambient
temperature of 400C, sweating rates of 198.6 ±19.3
g.H2o.m-2.h-1 were measured in the donkey.
Similarly, in the camel, sweating commenced at an
ambient temperature of 350C and at 400C, sweating rate
I was 164.5 ± 14.9 g.H -2 -1 . 2.m .h . Dehydratlon not only
delayed, but drastically reduced the rates of sweating
at all ambient temperatures, especially in the camel.
There was, however, an apparent increase in
respiratory evaporative heat loss during dehydration
in both species though TEHL decreased. Exposure to
high ambient temperature was accompanied by an
increase in body temperature in both species.
Subjection of dehydrated animals to high ambien
temperatures led to more rise of their body
temperatures than during hydration at anyone
temperature. At 40°C dehydrated camels had
temperature of 39.2oC while at 15°C their body
temperature was 35.6; a rise of 3.6oC.
Exposure of camels and donkeys to ambient
within the range 5°C to 40°C led to large
differences between the skin temperatures
extremities and the trunk. Large variations
skin temperature of the extremities were r
between ambient temperatures of 5°C·:to 20(
At ambient temperatures above 25°C, the ext rem:
temperatures and the trunk skin temperatUJ
similar. At 40°C, however, the skin temperat
the extremities were higher than that of the tl
It is concluded that both the donkey and 1
are efficient pack animals. They have lower el
costs of transport than other domestic species
including man. Body temperature increased dur
running and heat storage accounted for a major
the heat balance in both species. variations
skin temperatures of the extremities of both s
in hot and cold environments have a thermoreg
function. | en |
