Light intensity and performance of domestic pullets

Evidence from published trials is reviewed to investigate whether there is any need to change the recommended optimal light intensity for laying fowls from 5 lux. Although some recent trials have recorded excellent performanc es from birds exposed to light intensities of less than 5 lux, it is conclu ded that this has more to do with the ability of modern pullets to lay well even without photostimulation than with any change in the threshold of lig ht sensitivity. There is good recent evidence that the stimulation of early sexual maturity by a large increment in the photoperiod during the growing stage requires a minimal intensity of 2 lux, and that 4 lux is probably re quired for maximal response. By combining the results from all available tr ials, it is possible to demonstrate small but significant effects of light intensity on egg size, food intake and mortality. An economic analysis, whi ch takes into account all these responses, indicates that the optimal profi t occurs at about 5 lux. Although the prices used in that analysis are both local and ephemeral, the optimum will vary very little within other cost s tructures, because it is determined almost entirely by the lower outputs pr edicted at intensities below 5 lux and the greater electricity cost in prov iding very much higher intensities. It is recognised that, because maximisi ng profit is not always the sole objective in enterprises involving animal production, considerations for the welfare of both the livestock and worker s may make it prudent to recommend a slightly higher value such as 10 lux.