LIGHTING FOR LAYERS - WHAT WE KNOW AND WHAT WE NEED TO KNOW

Some principles of photoperiodism are reviewed. Increasing photoperiods advance sexual maturity and tend to stimulate higher rates of lay, Decreasing photoperiods have the opposite effects. Sensitivity to change in daylength varies with age and reproductive state. There is no one lighting programme which outyields all others: programmes providing different amounts and rates of increase in daylength during lay have often given the same egg output in the long run. However, egg output can be partitioned into more eggs and smaller ones, or fewer eggs but larger ones, by using light patterns in the growing stage which manipulate age at sexual maturity. A light intensity of about 5lux is adequate for laying hens and some strains may need even less than this. For both intensity and colour, lamps which are chosen to provide good working conditions will always meet the needs of the laying hen for light stimulation. Intermittent lighting can be used to reduce bird activity and particular programmes will result in lower mortality and a feed saving of 5%. Ahemeral cycles (such as 14L:13D) may have some value in increasing egg size in special circumstances if lightproof houses are already in use. It is proposed that future efforts should be devoted to producing a model which will predict age at 50% lay for any specified lighting programme, and will then predict rates of lay and egg size for particular stocks as a function of age at sexual maturity.