Climatic Change and Chicken Immunity
507
always beneficial at it minimal level. A minimal level of stress called as good stress is
required by all living organisms to perform a task. Stress becomes a distress when it
alters the normal biological functions like production and reproductive performances
of the chicken. Furthermore, stress mediated interactions with the immune system
suppress its normal functions and lead the chicken to a disease-prone status [24].
In general, chickens encounter various stressors such as thermal stress, production
stress, transportation stress, nutritional stress, immune stress, and stress due to crowding, drought and environmental conditions [56]. In the event of a climatic change,
stress due to adverse climatic conditions and emerging microbes and vector—borne
diseases are some of which the chickens have to encounter [57].
6 Molecular Responses to Heat Stress
High ambient temperature can adversely affect the structure and physiology of cells
causing impaired transcription, RNA processing, translation, oxidative metabolism,
membrane structure and function [58]. Cells generate small amounts of free radicals
or reactive oxygen species (ROS) during their normal metabolism. Although low
levels of ROS are essential in many biochemical processes, accumulation of ROS
may damage biological macromolecules i.e. lipids, proteins, carbohydrates and DNA
[59]. External factors such as heat can lead to increased free radicals and other ROS
and may lead to oxidative stress [60].
Increased mitochondrial reactive oxygen species (ROS) production and decreased
avian uncoupling protein was confirmed in HS birds [55]. Heat stress could cause
oxidative damage and lead to accumulation of free radicals and other reactive oxygen species (ROS). The balance between ROS and antioxidant is retarded in broilers
exposed to HS [61], leading to oxidative stress during acute HS [15, 62]. Malondialdehyde is a biomarker applied to measure oxidative stress in chickens by indirectly
measuring the level of peroxidation due to ROS [55]. In order to establish this balance
during HS, the strategy for increasing antioxidant capability and activity in birds is
required [43].
Antioxidants, both enzymatic (viz. superoxide dismutase, glutathione peroxidase
and catalase) and non-enzymatic (vitamins C, E and A, glutathione, pyruvate etc.)
provide necessary defense against oxidative stress generated due to high ambient
temperature. In such conditions, the administration of antioxidants has proved to be
useful for improvement of several immune functions [63]. The immune cell functions are associated with the production of ROS such as that involved in the microbial
activity of phagocytes or lymph proliferative response to mitogens [64, 65]. However excessive production of ROS due to heat stress renders harmful effect on cells
of immune system. When exposed to oxidative stress, polymorph nuclear leukocytes
(PMNs) change their pattern of oxygen uptake sharply while releasing large amounts
of superoxide anion into the cell environment. PMNs play an important role as mediators of tissue destructive events in inflammatory diseases, ranging from rheumatoid
arthritis and myocardial reperfusion injury to respiratory distress syndrome [66].
507
always beneficial at it minimal level. A minimal level of stress called as good stress is
required by all living organisms to perform a task. Stress becomes a distress when it
alters the normal biological functions like production and reproductive performances
of the chicken. Furthermore, stress mediated interactions with the immune system
suppress its normal functions and lead the chicken to a disease-prone status [24].
In general, chickens encounter various stressors such as thermal stress, production
stress, transportation stress, nutritional stress, immune stress, and stress due to crowding, drought and environmental conditions [56]. In the event of a climatic change,
stress due to adverse climatic conditions and emerging microbes and vector—borne
diseases are some of which the chickens have to encounter [57].
6 Molecular Responses to Heat Stress
High ambient temperature can adversely affect the structure and physiology of cells
causing impaired transcription, RNA processing, translation, oxidative metabolism,
membrane structure and function [58]. Cells generate small amounts of free radicals
or reactive oxygen species (ROS) during their normal metabolism. Although low
levels of ROS are essential in many biochemical processes, accumulation of ROS
may damage biological macromolecules i.e. lipids, proteins, carbohydrates and DNA
[59]. External factors such as heat can lead to increased free radicals and other ROS
and may lead to oxidative stress [60].
Increased mitochondrial reactive oxygen species (ROS) production and decreased
avian uncoupling protein was confirmed in HS birds [55]. Heat stress could cause
oxidative damage and lead to accumulation of free radicals and other reactive oxygen species (ROS). The balance between ROS and antioxidant is retarded in broilers
exposed to HS [61], leading to oxidative stress during acute HS [15, 62]. Malondialdehyde is a biomarker applied to measure oxidative stress in chickens by indirectly
measuring the level of peroxidation due to ROS [55]. In order to establish this balance
during HS, the strategy for increasing antioxidant capability and activity in birds is
required [43].
Antioxidants, both enzymatic (viz. superoxide dismutase, glutathione peroxidase
and catalase) and non-enzymatic (vitamins C, E and A, glutathione, pyruvate etc.)
provide necessary defense against oxidative stress generated due to high ambient
temperature. In such conditions, the administration of antioxidants has proved to be
useful for improvement of several immune functions [63]. The immune cell functions are associated with the production of ROS such as that involved in the microbial
activity of phagocytes or lymph proliferative response to mitogens [64, 65]. However excessive production of ROS due to heat stress renders harmful effect on cells
of immune system. When exposed to oxidative stress, polymorph nuclear leukocytes
(PMNs) change their pattern of oxygen uptake sharply while releasing large amounts
of superoxide anion into the cell environment. PMNs play an important role as mediators of tissue destructive events in inflammatory diseases, ranging from rheumatoid
arthritis and myocardial reperfusion injury to respiratory distress syndrome [66].