Lighting and mortality rates in domestic fowl.

1. Data from intermittent and conventional lighting trials were analysed to investigate the effect of daily illumination upon mortality during the laying period and in 49-d-old broilers. 2. Liveability in laying hens was improved by the use of intermittent lighting: the degree of improvement was proportional to the reduction in daily illumination achieved by the intermittent programme. 3. The reduction in mortality with intermittent lighting in laying hens was not the result of intermittent lighting per se. Intermittent regimens which did not reduce daily illumination did not reduce mortality. 4. Mortality in both conventionally-lit laying hens and 49-d old-broiler chickens increased with photoperiod.