Heat Stress Management in Poultry
A rise in environmental temperature during summer season has undesirable effect on polutry production. Poultry is one of the pivotal sector for production of good quality protein production. Surge in environmental temperature during summer season is the major stressor in poultry production. Heat stress has harsh effects on growth, feed intake, production performance in terms of drop in egg production and quality of meat and increase in chick mortality. As sweat glands are absent, chicken majorly depend on panting to liberate heat from the body to environment. Loss of gut integrity during heat distress results in decrease nutrient absorption from the intestine and altered microflora due to leakage of pathogens. Consequently, immune response in the body is triggered against the pathogens (Galarza-Seeber et al., 2016). Birds exposed to heat stress are associated with generation of more reactive oxygen species in the tissue causing cell disruption. Several approaches have been reviewed by the researchers to overcome the adverse effects of heat stress on poultry production. Supplementation of feed additives is the most feasible manner to enhance productive performance in birds during summer. Supplement of nutrients in the form of vitamins, minerals, probiotics and herbal products are consistently required to withstand the environmental stress during summer season. Selective breeding of heat tolerant and high performance breeds to enhance the progeny quality. Subjecting the chicks of early age to thermal conditioning also enables them to withstand high temperature in later stages of life. Poultry rearing is majorly practiced for meat and egg production as they form good source of protein. Due to improvised genetic selection, enhanced nutritional status broilers reach marketable age within 35 days and layers produces around 200 eggs in a year. Birds under heat stress show reduction in body weight, feed intake and increment in feed conversion ration. During heat stress release of appetite related hormones such as cholecystokinin and ghrelin can result in anorexia. Further bodyweight is related to feed intake, suppressed feed intake during heat stress is attributed with reduced body weight gain. The performance of layers also effected, due to decreased shell weight and shell thickness. In poultry due to lack of sweat glands dissipation of body temperature is through increased respiration rate. There is a increase of 0.56 breaths per minute for every temperature-humidity unit increment (Mutibvu et al., 2017).Respiratory alkalosis is a status of the body when pH of the blood pH rises above the normal range which is often resulted from accelerated respiratory rates and change in the ratio of bicarbonate to carbon dioxide. Heat stress adversely effects the integrity of gut epithelial barrier resulting entry of pathogens and decreased absorption of nutrients, which is characterized as “leaky gut syndrome”. Enhanced entry of harmful pathogens like Escherichia coli, Clostridium sp., and, Salmonella sp., results in decreasing the immune performances. Moreover immune organs such as bursa of fabricius, thymus and spleen tend to decrease in activity in birds under heat stress. Oxidative injury due to release of reactive oxygen species is of major concern in birds subjected to heat stress.
Strategies to overcome the adverse effects of heat stress:
Raise in environment temperatures globally stresses the need to discuss over various strategies to overcome the effect of heat stress on poultry.Environment and housing: To avoid stress due to crowding of flocks reduce the stocking density, proper ventilation and cooling systems can be ensured in the rearing systems.
Nutritional management: considering nutritional supplements to withstand the stress created during summer along with supply of cool water is an easily adaptable strategy. Drinking water enriched with required electrolytes helps in acid-base balance and enhance heat tolerant capacity in birds. Dietary supplementation of vitamins such as A,C and E along with required minerals helps in enhancing egg production, fertility and hatchability along with decrease in shell breakage and mortality associated with heat stress. Supplementation of vitamins and minerals have a major role during the adaptation period of heat stress. Especially dietary inclusion of vitamin C and E strengthens the egg shell quality, improves feed intake and body weights of broilers and quails reared under heat stress ( El-Gawad et al 2008). Vitamin E helps in improving feed intake, egg quality, enhance fatty acid composition, specially has a free radical quenching activity which helps as a first line of defense against free radicals produced under heat stress. Minerals such as selenium possess antioxidant properties through improving levels of glutathioneglutathione peroxidase system. A combination of feed enriched with vitamins, minerals along with probiotics has a synergistic effect on minimizing the stress during summer. Probiotics containing products such as lactobacillus culture help in colonizing beneficial bacterial and reduce the harmful bacteria in intestine. Studies documented that supplementation of probiotics has pronounced effects on stressed birds in improving feed intake and feed efficiency.
Selection of breeding stock: selection of a good quality stock to produce next progeny is termed as genetic selection. Meat type chicken such as broilers are majorly targeted for rapid growth in bodyweight. However,under heat stress rapid growersexhibit deprived feed intake due to lesser heat tolerant capacity in comparison with slow growing broilersAwad et al., 2019). Similarly egg production is the major criteria for laying hens. Layers under heat stress are much more susceptible which adversely impacts the egg production and egg quality. Hence, genetic selection of birds based on heat tolerant capacity helps in improving the performance of birds during summer.
Early age thermal conditioning: The demand for fast growing chicks which produce more weight gain in a minimum time is increasing day by day. However, fast growing chicks due to their high metabolic rate are more prone to heat stress. Changes in the environmental temperatures are adjusted by regulating internal body temperature by various mechanisms such as panting. It is essential to decrease the body temperature to make the birds more tolerant to heat stress. Studies suggested that 24 h thermal conditioning of 5 day old chick at 40°C resulted in reducing the bird body temperature ((De Basilio et al., 2003). Subjecting the chicks in the very first few days may help in developing the temperature regulatory mechanisms, which helps in withstanding the heat stress in later stages of life.
Conclusion: Considering the adverse effects such as decreased feed intake, body weight, shell thickness, mortality due to heat stress combination of strategies must be adopted to avoid loss to poultry sector. Adoption of proper rearing system with good ventilation, proper housing condition and following recommended stocking density are essential to improve the performance parameters during summer. Dietary supplementation with vitamins, minerals,probiotics and bioactive compounds helps in minimizing the adverse effects of heat stress. Procurement of progeny with heat tolerant capacity can also show promising results.
Dr K. Kasturi Devi¹ and Dr. Beesam Srinu²
Assistant Professor
¹Department of Veterinary Pharmacology & Toxicology,
²Department of Veterinary Public Health & Epidemiology
C.V.Sc., Mamnoor
