Climatic Change and Chicken Immunity
505
In the formula, db is defined as the dry bulb temperature in °F and RH is the relative
humidity (RH%/100). The obtained values are used to establish the severity of HS:
86 indicates extreme severe HS [27]. THI, however, does not account for important
climatic variables such as air movement or solar radiation. In addition, THI does not
include management or animal factors, such as the effect of shade or the genotype and
phenotypic differences. Several other formulas have been developed for determining
the HS potential to account for the additional factors. Tao and Xin [29], for example,
made improvements on the THI by creating the temperature-humidity-velocity index
(THVI), which includes wind speed to determine the HS level in poultry. Wind speed
has been shown to be favorable to chicks exposed to HS conditions [22]. Therefore,
the following formula of THVI may be advantageous to improve the method in
determining the severity of HS.
THVI = (0.85 × DBT + 0.15 × WBT) × V − 0.058
In the formula, DBT is defined as the dry bulb temperature in °C, WBT is the
wet bulb temperature in °C, and V represents the air velocity. Similarly to THI, the
obtained numerical values are used to establish the negative effects of HS: ≤70 being
normal, 70–75 indicates alert, 76–81 being in danger, and ≥82 indicating emergency
[29]. Additional indices have incorporated the previously stated variables to overcome the limitations of different THI [30]. For example, Mader et al. [31] developed
a comprehensive climate index applicable under a wide range of environmental conditions by providing an adjustment to ambient temperature, relative humidity, wind
speed, and radiation.
4.3 Impact of Heat Stress
Stress, a response to adverse stimuli, is difficult to define and understand because of
its nebulous perception. Stress is the nonspecific reaction of the body to any request,
though stressor can be characterized as “an operator that produces worry”. Therefore,
stress represents the biological reaction of the chicken organism to stimuli that disturb
its normal physiological equilibrium or homeostasis.
Heat stress results from a negative balance between the net amount of energy
flowing from the chicken’s body to its surrounding environment and the amount of
heat energy produced by the chicken. Heat stress is a critical stressor, especially
in regions with hot climates and farms unable to control the ambient temperature
[14, 32]. HS has been consistently found to prohibit the chicken production. In
general, temperature variation affects the endocrine system, which controls chicken
metabolism, growth and reproduction, which implies that a decrease or increase in
temperature will have an impact on avian production. It includes a decrease in feed
intake [33–35], impaired growth performance [36–38], decrease in egg production
[39–42], impaired egg qualities [21, 40, 43], and an increase in mortality [41, 44].
Consolidation of these results was speculated by Mack et al. [40]. The egg production
505
In the formula, db is defined as the dry bulb temperature in °F and RH is the relative
humidity (RH%/100). The obtained values are used to establish the severity of HS:
86 indicates extreme severe HS [27]. THI, however, does not account for important
climatic variables such as air movement or solar radiation. In addition, THI does not
include management or animal factors, such as the effect of shade or the genotype and
phenotypic differences. Several other formulas have been developed for determining
the HS potential to account for the additional factors. Tao and Xin [29], for example,
made improvements on the THI by creating the temperature-humidity-velocity index
(THVI), which includes wind speed to determine the HS level in poultry. Wind speed
has been shown to be favorable to chicks exposed to HS conditions [22]. Therefore,
the following formula of THVI may be advantageous to improve the method in
determining the severity of HS.
THVI = (0.85 × DBT + 0.15 × WBT) × V − 0.058
In the formula, DBT is defined as the dry bulb temperature in °C, WBT is the
wet bulb temperature in °C, and V represents the air velocity. Similarly to THI, the
obtained numerical values are used to establish the negative effects of HS: ≤70 being
normal, 70–75 indicates alert, 76–81 being in danger, and ≥82 indicating emergency
[29]. Additional indices have incorporated the previously stated variables to overcome the limitations of different THI [30]. For example, Mader et al. [31] developed
a comprehensive climate index applicable under a wide range of environmental conditions by providing an adjustment to ambient temperature, relative humidity, wind
speed, and radiation.
4.3 Impact of Heat Stress
Stress, a response to adverse stimuli, is difficult to define and understand because of
its nebulous perception. Stress is the nonspecific reaction of the body to any request,
though stressor can be characterized as “an operator that produces worry”. Therefore,
stress represents the biological reaction of the chicken organism to stimuli that disturb
its normal physiological equilibrium or homeostasis.
Heat stress results from a negative balance between the net amount of energy
flowing from the chicken’s body to its surrounding environment and the amount of
heat energy produced by the chicken. Heat stress is a critical stressor, especially
in regions with hot climates and farms unable to control the ambient temperature
[14, 32]. HS has been consistently found to prohibit the chicken production. In
general, temperature variation affects the endocrine system, which controls chicken
metabolism, growth and reproduction, which implies that a decrease or increase in
temperature will have an impact on avian production. It includes a decrease in feed
intake [33–35], impaired growth performance [36–38], decrease in egg production
[39–42], impaired egg qualities [21, 40, 43], and an increase in mortality [41, 44].
Consolidation of these results was speculated by Mack et al. [40]. The egg production