An update on heat stress in laying hens

SUMMARY Heat stress is one of the environmental stressors challenging global poultry industry and lowers performance and welfare of chickens leading to significant economic loss. It triggers the hypothalamic-pituitary-adrenal cortical system, which releases a corticotrophin-releasing factor from the hypothalamus. This then leads to an increase in corticosterone levels. The harmful effects of heat stress on laying hens include decreased laying performance, feed intake, egg quality, metabolic rate, and immune state in laying hens. Additionally, heat stress induces negative regulation of metabolic hormones, endocrine systems, acid-base balance, antioxidant balance, and poor physiological functioning of internal digestive and reproductive organs. Therefore, it is important to mitigate heat stress to maintain maximum production efficiency. This review article explores the impact of heat stress on production, behaviour, physiology, gut health, oxidative stress, and immune responses in laying hens. It emphasises the environmental factors that contribute to heat stress and the behavioural and physiological host responses.