Climatic Change and Chicken Immunity
513
feed may avoid the thermogenic effect associated with nutrient absorption, assimilation, and utilization [109]. When the environmental temperature increases above
30 °C, several mechanisms are activated to allow the blood flow increase to upper
respiratory tract and other active organs for heat dissipation (combs and wattles) at
the cost of blood flow to the digestive system [110]. Wolfenson et al. [54] showed a
descending gradient of blood flow along the digestive tract from the ileum to proventriculus in response to hyperthermia. This would reduce proteolytic enzymatic activities occurring in the upper part of the digestive tract and decreases subsequent protein
digestibility [111]. It is necessary to establish specific digestibility coefficients for
high environmental temperature conditions. The reduction of triiodothyronine and
changes in bodily hemodynamics has been suggested to be part of the mechanisms
associated with improved thermotolerance in acclimated chickens [112]. The high
ambient temperature may suppress nitrogen and total amino acids ileal digestibility
by almost 4.5 and 5.5%, respectively [77].
It has been reported that chicks fed deficient amino acid had suboptimal interleukin
production during immunologic stress. Rama-Rao et al. [113] showed that methionine levels lower than 0.50% in broiler diet generates a poorer immune cell response as
compared to higher concentrations. Utilization of immune stimulants is one solution
to improve the immunity of chickens and to decrease their susceptibility to infectious diseases [8]. Glucose is the primary energy source for all metabolic reactions.
The plasma glucose concentration is primarily regulated by hormones secreted by
the pancreas. The hormones glucagon and insulin function to increase and decrease
glucose levels, respectively. Disturbances to this balance can result in damage to
nerves, blood vessels, and even death. Changes in physiology may occur by alterations in electrolyte balance which is essential for acid-base balance, maintenance
of cellular homeostasis, synthesis of tissue protein, electrical potential of cell membranes, enzymatic reactions, and maintaining osmotic pressure [48]. Increased fluid
excretion in the urine is accompanied by increased concentrations of electrolytes in
the urine [49]. Altering electrolyte amounts in feed partially ameliorates the negative
impacts of heat stress in broiler chickens [2].
Antioxidant vitamins are effective ways of alleviating heat stress in poultry.
Antioxidant vitamins such as vitamins A (retinol), E (α tocopherol) and C (ascorbic
acid) are used in poultry diets because of their anti-stress effects and because their
synthesis is reduced during heat stress. Heat stress stimulates the release of corticosterone and catecholamines and initiates lipid peroxidation in cell membranes
[18].
Modern herbs research and a new understanding of the immune system have
explained many mechanisms by which these herbs work. Instead, they rely on the
innate immunity of each cell and on systemic signals emanating from infection
sites [114, 115]. Flavonoids and hydroxylase phenols are naturally synthesized by
plants in response to infection [116]. Flavones and flavanones, being bitter, also have
natural anti-feeding effects. Alkaloids are the most common plant metabolites [117].
More recently, many secondary metabolites have been suggested to have Immunomodulation properties in chickens [118].
513
feed may avoid the thermogenic effect associated with nutrient absorption, assimilation, and utilization [109]. When the environmental temperature increases above
30 °C, several mechanisms are activated to allow the blood flow increase to upper
respiratory tract and other active organs for heat dissipation (combs and wattles) at
the cost of blood flow to the digestive system [110]. Wolfenson et al. [54] showed a
descending gradient of blood flow along the digestive tract from the ileum to proventriculus in response to hyperthermia. This would reduce proteolytic enzymatic activities occurring in the upper part of the digestive tract and decreases subsequent protein
digestibility [111]. It is necessary to establish specific digestibility coefficients for
high environmental temperature conditions. The reduction of triiodothyronine and
changes in bodily hemodynamics has been suggested to be part of the mechanisms
associated with improved thermotolerance in acclimated chickens [112]. The high
ambient temperature may suppress nitrogen and total amino acids ileal digestibility
by almost 4.5 and 5.5%, respectively [77].
It has been reported that chicks fed deficient amino acid had suboptimal interleukin
production during immunologic stress. Rama-Rao et al. [113] showed that methionine levels lower than 0.50% in broiler diet generates a poorer immune cell response as
compared to higher concentrations. Utilization of immune stimulants is one solution
to improve the immunity of chickens and to decrease their susceptibility to infectious diseases [8]. Glucose is the primary energy source for all metabolic reactions.
The plasma glucose concentration is primarily regulated by hormones secreted by
the pancreas. The hormones glucagon and insulin function to increase and decrease
glucose levels, respectively. Disturbances to this balance can result in damage to
nerves, blood vessels, and even death. Changes in physiology may occur by alterations in electrolyte balance which is essential for acid-base balance, maintenance
of cellular homeostasis, synthesis of tissue protein, electrical potential of cell membranes, enzymatic reactions, and maintaining osmotic pressure [48]. Increased fluid
excretion in the urine is accompanied by increased concentrations of electrolytes in
the urine [49]. Altering electrolyte amounts in feed partially ameliorates the negative
impacts of heat stress in broiler chickens [2].
Antioxidant vitamins are effective ways of alleviating heat stress in poultry.
Antioxidant vitamins such as vitamins A (retinol), E (α tocopherol) and C (ascorbic
acid) are used in poultry diets because of their anti-stress effects and because their
synthesis is reduced during heat stress. Heat stress stimulates the release of corticosterone and catecholamines and initiates lipid peroxidation in cell membranes
[18].
Modern herbs research and a new understanding of the immune system have
explained many mechanisms by which these herbs work. Instead, they rely on the
innate immunity of each cell and on systemic signals emanating from infection
sites [114, 115]. Flavonoids and hydroxylase phenols are naturally synthesized by
plants in response to infection [116]. Flavones and flavanones, being bitter, also have
natural anti-feeding effects. Alkaloids are the most common plant metabolites [117].
More recently, many secondary metabolites have been suggested to have Immunomodulation properties in chickens [118].