Thermoregulatory and Systemic Challenges in Broiler Chickens under Heat Stress

Abstract

Broiler chicken production constitutes a major component of the global poultry industry and significantly contributes to food security through the provision of affordable animal protein. However, heat stress remains one of the most severe environmental constraints affecting broiler productivity, particularly in tropical and subtropical climates. This review examines the thermoregulatory and systemic challenges associated with heat stress in broiler chickens. The thermoneutral balance of broilers is upset by high relative humidity, elevated ambient temperature, and increased radiant heat. This leads to decreased feed intake, poor growth performance, higher mortality, and degraded well-being. Heat stress triggers the hypothalamic-pituitary-adrenal axis, resulting in endocrine and metabolic changes that impair immune function and overall productivity. Broiler chickens exhibit several behavioural and physiological adaptations to dissipate excess body heat, including panting, wing spreading, increased water consumption, and reduced physical activity. The overproduction of reactive oxygen species, which causes oxidative stress when antioxidant defenses are overpowered, is one of the main effects of heat stress. Reactive oxygen species are crucial for immunological responses and cellular signaling. When they are produced in excess, they damage lipids, proteins, and nucleic acids, compromising cellular integrity and physiological processes. The antioxidant defence system, comprising enzymatic antioxidants such as superoxide dismutase, catalase, and glutathione peroxidase, as well as non-enzymatic antioxidants, plays a vital role in maintaining redox homeostasis under thermal stress. Developing efficient management and dietary methods to enhance broiler health, welfare, and productivity in demanding conditions requires an understanding of the relationships among heat stress, oxidative state, and thermoregulatory responses.