LAUSR

SUMMARY Worldwide, commercial laying hens are frequently being used for only one production cycle mainly due to a decline in egg quality and/or egg quantity at 70–80 weeks of age. Extending the production cycle of these hens by improving or maintaining their egg quality and laying persistency could lead to both economic and environmental benefits as well as a more sustainable egg industry. Laying performance of the modern-day laying hen is highly dependent upon the light source used during housing and artificial lighting programmes have been used for years to control egg production. Birds are able to perceive coloured light (400–700 nm) as well as the ultraviolet (UV) part of the spectrum (100–400 nm) due to the presence of an extraretinal cone in the eye. Studies have shown that red light, due to its longer wavelength of 660 nm, is able to stimulate the hypothalamus and elicit a photosexual response in all animals including birds. This can result in increased egg production in comparison to green, blue or white light exposure, although responses may vary depending on bird strain and the intensity of the light used. UV light has a shorter wavelength (100–400 nm) than visible light (400–700 nm) and so its effects on egg production are likely to be weak to non-existent. The benefits of UV light are mediated through its ability to activate cholecalciferol from 7-dehydroxycholesterol in the skin resulting in improvements in eggshell quality. These improvements in shell quality are most likely to occur in birds that are exposed to (natural) daylight, as UV light can compensate to some extent, the lack of vitamin D in poultry diets. This review highlights the variable effects of light of different wavelengths and intensity on laying hen production, egg quality and its potential to extend the end of lay in commercial hens.