Poultry and coloured light

Poultry have four types of cone in the retina of the eye, and this means th at they probably see colour differently from trichromatic humans. Notwithst anding the fact that humans and birds have maximum sensitivity in a similar part of the spectrum (545-575 nm), poultry are likely to perceive light fr om various types of lamp at a different intensity from humans because they are more sensitive to the blue and red parts of the spectrum. Although colo ur has been confounded with illuminance in many trials, wavelength has an u nquestionable effect on poultry production and behaviour. Growth and behavi our responses depend principally on retinal photoreception, whereas photose xual responses are mainly influenced by hypothalamic light reception. In tu rkeys and chickens growth under red illumination is inferior to that under blue or green light, and this may be a result of birds exposed to red light being more active and showing more aggression than birds exposed to shorte r wavelength radiation. In contrast, the easier penetration of longer wavel ength radiation to the hypothalamus makes red light more sexually stimulato ry than blue or green, although the hypothalamic photoreceptors are more se nsitive to blue/green light when illuminated directly. Egg production trait s, however, appear to be minimally affected by wavelength.