506
A. M. M. Hamdy
is dependent on gonadal steroids, such as progesterone, testosterone, and negatively
affects the bioactivity of gonadotropin is less understood. Most likely, it is due to
multiple factors affecting animals’ physiological homeostasis under HS, such as a
reduction in feed intake and an increase in oxidative stress [15].
The variability of the effects of HS on chicken health may be explained by the
examined birds, such as health and production status, and/or genetic background.
The variation may also be due to the variety of intensity and duration of HS applied
to the chickens. Stocking density is also a major factor affecting chicken productivity
and physiological homeostasis, as well [20].
4.4 Heat Regulation
Chickens produce and dissipate heat to maintain a relatively constant body temperature. When the temperature and relative humidity exceed the comfort level, chickens
lose their ability to efficiently dissipate heat, which then leads to behavioral and physiological changes [14, 45–47]. Chickens become heat stressed without the balance
between heat production and heat dissipation, or thermoregulation. Chickens do not
have sweat glands. Therefore, the primary methods of heat loss include respiratory
evaporative cooling, or panting and conductive heat transfer through their feet and
wattles [48]. Likewise, panting relies on water loss which may lead to dehydration
[49] or respiratory alkalosis [50]. Chickens have air sacs as an additional mechanism
to promote heat exchange between their body and the environment. Air sacs are useful during panting, as they promote air circulation on surfaces, increasing heat loss
via evaporation along with gas exchanges [51]. Sensible heat is used by chickens
to release heat, including radiation, convection, and conduction [52, 53]. However,
some methods of heat loss are challenging to the avian species due to their feather
coverage trapping heat to prevent hypothermia. During HS, capillary blood flow is
redistributed throughout the body to improve sensible heat loss [54]. Mujahid et al.
[55] presented evidence that broiler chickens exposed to different durations of acute
HS resulted in distinct time-dependent physiological responses.
5 Impact of Heat Stress on Chicken Health
To maintain flocks of chicks in good health managers should ensure that: (1) The
challenge is kept as low as possible and (2) The flocks’ ability to fight infection is
kept as high as possible.
In some cases, the chicks’ immune system requires frequent support to be powerful
against an antigen, while in different cases, less incessant incitement is required. In
a few circumstances, it is conceivable to rely upon the natural infection to trigger the
immune system to produce the antibodies [7]. However, in these cases it is necessary
to take precautions to ensure that the infection does not get out of control. Stress is
A. M. M. Hamdy
is dependent on gonadal steroids, such as progesterone, testosterone, and negatively
affects the bioactivity of gonadotropin is less understood. Most likely, it is due to
multiple factors affecting animals’ physiological homeostasis under HS, such as a
reduction in feed intake and an increase in oxidative stress [15].
The variability of the effects of HS on chicken health may be explained by the
examined birds, such as health and production status, and/or genetic background.
The variation may also be due to the variety of intensity and duration of HS applied
to the chickens. Stocking density is also a major factor affecting chicken productivity
and physiological homeostasis, as well [20].
4.4 Heat Regulation
Chickens produce and dissipate heat to maintain a relatively constant body temperature. When the temperature and relative humidity exceed the comfort level, chickens
lose their ability to efficiently dissipate heat, which then leads to behavioral and physiological changes [14, 45–47]. Chickens become heat stressed without the balance
between heat production and heat dissipation, or thermoregulation. Chickens do not
have sweat glands. Therefore, the primary methods of heat loss include respiratory
evaporative cooling, or panting and conductive heat transfer through their feet and
wattles [48]. Likewise, panting relies on water loss which may lead to dehydration
[49] or respiratory alkalosis [50]. Chickens have air sacs as an additional mechanism
to promote heat exchange between their body and the environment. Air sacs are useful during panting, as they promote air circulation on surfaces, increasing heat loss
via evaporation along with gas exchanges [51]. Sensible heat is used by chickens
to release heat, including radiation, convection, and conduction [52, 53]. However,
some methods of heat loss are challenging to the avian species due to their feather
coverage trapping heat to prevent hypothermia. During HS, capillary blood flow is
redistributed throughout the body to improve sensible heat loss [54]. Mujahid et al.
[55] presented evidence that broiler chickens exposed to different durations of acute
HS resulted in distinct time-dependent physiological responses.
5 Impact of Heat Stress on Chicken Health
To maintain flocks of chicks in good health managers should ensure that: (1) The
challenge is kept as low as possible and (2) The flocks’ ability to fight infection is
kept as high as possible.
In some cases, the chicks’ immune system requires frequent support to be powerful
against an antigen, while in different cases, less incessant incitement is required. In
a few circumstances, it is conceivable to rely upon the natural infection to trigger the
immune system to produce the antibodies [7]. However, in these cases it is necessary
to take precautions to ensure that the infection does not get out of control. Stress is