Shahla Perween, Asmita Singh, Tony Jose and Jatin Kumar Sahoo
Ph.D Scholar, ICAR- Indian Veterinary Research Institute, Izatnagar
Introduction: Heat stress is associated with compromised performance and productivity in poultry due to declines in feed intake, nutrient utilization, growth rate, egg production and quality, and feed efficiency. Emerging evidences have shown that acute heat exposure results in increased production of free radicals and causes oxidative damage to lipids, proteins, and DNA. Additionally, heat stress can influence immune response by changing the expression of cytokines and by making the immune cells more susceptible to oxidative stress. Selenium, as a part of specific selenoproteins, can help to maintain antioxidant defences, thereby preventing damages to tissues. An optimum response with supplementation of selenium in diet has been found to improve feed intake, body weight gain, feed efficiency, egg production and quality, and antioxidant status in heat-stressed poultry.
Selenium: Selenium plays important roles in the regulation of various metabolic processes within the body and is an integral part of at least 25 selenoproteins, some of which have important enzymatic functions. The National Research Council recommends a level of 0.1 to 0.15 mg/kg of selenium in various poultry diets. Because many natural feed ingredients are marginally selenium deficient, this micronutrient is commonly supplemented to diets for poultry. Sodium selenite and sodium selenate have been the most common forms of selenium supplementation in poultry diets. From various study it was found that the organic forms of selenium, selenomethionine and selenium–yeast, may be more available to the chick than the inorganic forms of selenium. Absorption of selenium occurs mainly at the lower end of the small intestine. Both forms of selenium, organic as well as inorganic, are readily absorbed. In general, organic forms are absorbed more efficiently than are inorganic forms (particularly selenite).
Selenium deficiency causes loss of appetite and reduced efficiency of feed utilization and thus leads to growth retardation. Feather development and structure are affected by selenium deficiency. Blood selenium concentrations are lower, and the activity of several enzymes in metabolic pathways decreased in selenium-deficient animals.
Effect of Selenium Supplementation in Heat-Stressed Poultry
- Performance and Productivity: Selenium deficiency in animals is characterized by loss of appetite and body weight, low activity of glutathione-requiring enzymes, and increased production of free radicals. Selenium positively affects feed utilization through participation in the metabolism of carbohydrates, lipids, and proteins. Selenium (0.3 mg/kg) supplementation on performance responses in broilers reared under heat stress or thermoneutral condition and reported that live weight gain, feed conversion ratio, and dressing percentages were greatest with selenium supplementation in both conditions.
Supplementation of organic form of selenium into the laying hen diet increased eggshell strength, improved Haugh units and also reduced the deterioration of the albumen, which results in slower carbon dioxide loss and thus maintains albumen quality after the egg is laid.
- Nutrient Digestibility: High ambient temperatures are associated with lower nutrient digestibility in poultry, the digestibilities of dry matter, organic matter, crude protein, and ether extract decreased in birds. In a recent study, it was demonstrated that the concentration of selenium in the blood and duodenal mucosa, and the activities of thioredoxin reductase and glutathione peroxidase in the duodenal mucosa significantly increased in birds supplemented with selenium in their diet. Thus, the addition of selenium into the diet can protect the small intestine against oxidative stress. The role of selenium in protecting the pancreatic tissue against oxidative damage has also been well established, since it may help the pancreas and small intestine to function properly, thus improving the digestibility of nutrients.
- Antioxidant Status: Heat stress results in increased free radical production and lowers the concentrations of antioxidant vitamins and minerals such as A, C, E, and selenium in serum. The impaired membrane integrity in breast muscle of heat-stressed broiler chicks was also considered to be related with the changed redox balance because broiler chicks that were exposed to heat stress exhibited more than a twofold increase of MDA (malonaldehyde) in the skeletal muscle. Studies show that concentrations of MDA in serum decrease with dietary selenium supplementation in heat-stressed broiler birds. Hence selenium supplementation increased the activity of glutathione peroxidase and decreased the concentration of MDA in the breast muscle of heat-stressed birds.
- Immune status: The heterophile to lymphocyte (H/L) ratio has been used as a reliable indicator of stress in birds. Under high environmental temperature H/L ratio was increased which indicates a relationship between heat stress and non-specific immune reactive cells. Selenium is an essential element for the efficient and effective operation of the immune system and is critical for the integrity of the cells involved in the immune response. Selenium deficiency causes a decrease in phagocytic functions of macrophages and adversely affects interleukin production. The fall in blood selenium is also causes a reduction in CD4+ T-helper cells. These are cells that recognize viral antigen on the surface of infected cells and release chemotactic factors and cytokines that activate the cells to become resistant to infection. From various study it was found selenium improve immune status during heat stress, supplementation of selenium in broiler chicks reared in either a thermoneutral or heat stress environment its higher total IgM and IgG antibody titers, indicating that selenium supplementation can alleviate the deleterious effects of heat stress.
Conclusions: In conclusion, heat stress causes significant decreases in performance, productivity, nutrient utilization, and immune and antioxidant statuses, which result in increases in disease incidences and economic losses in poultry operations. Because it has several significant functions as well as antioxidant properties, selenium is one of the most important components of the poultry diet during exposure to heat stress.