Lighting programs in broiler and layer chicken houses significantly affect welfare through their impact on sleep, circadian rhythms, and the expression of natural day-active behaviors.
Lighting welfare in poultry houses is a relatively low-cost intervention with significant welfare impact. Continuous or near-continuous lighting — used historically to maximize feed intake — disrupts sleep, causes retinal damage, and impairs the circadian regulation of immune and metabolic function. Chickens evolved with regular day-night cycles, and their physiology requires darkness for restorative sleep and normal hormonal rhythms. Providing adequate darkness is not merely a regulatory requirement but a biological necessity. The welfare improvements from adequate dark periods extend across multiple domains: better leg health, reduced metabolic disease, normal sleep behavior, and improved immune competence. These improvements often align with production benefits — birds with better leg health and lower cardiovascular disease have better welfare and better commercial outcomes simultaneously.