Integrated Stress Physiology and Mitigation Strategies for Heat Stress in Layer Chickens—Review

Heat stress is a major constraint to global egg production, as rising temperatures increasingly challenge the physiological limits of commercial layer chickens. This review integrates current advances in stress physiology to demonstrate that heat stress is not merely a thermoregulatory problem but a multi-systemic disruption involving neuroendocrine overload, metabolic imbalance, oxidative damage, immune suppression, and gastrointestinal barrier breakdown. These interacting pathways collectively impair egg production, shell quality, feed efficiency, and hen welfare. The review also synthesizes emerging mitigation strategies across environmental control, nutritional interventions, genetic and breeding innovations, welfare-oriented housing systems, and precision monitoring technologies. Studies indicate that targeted cooling, antioxidant, and electrolyte supplementation, the selection of heat-tolerant strains, enriched environments, and sensor-based early-warning systems can significantly enhance egg-laying hen resilience. Remaining gaps include a limited understanding of multi-stressor interactions, microbiome-mediated thermal tolerance, and the large-scale implementation of precision tools. The review provides a forward-looking framework for improving heat resilience in modern layer systems.