a1 Animal and Poultry Science, University of KwaZulu-Natal, Pietermaritzburg, South Africa
Poultry, unlike humans, have a fourth retinal cone that allows them to see in the UVA part of ultraviolet radiation. This ocular function is principally used by poultry to modify various behavioural functions such as feeding, peer recognition, mate selection, mating activity, and social encounters. Retinally perceived UVA controls the release of melatonin in the pineal gland of dark-adapted birds. Ultraviolet radiation has shorter wavelengths than visible light, and, as a result, is unable to penetrate to the hypothalamus to induce a photosexual response; UV is thus minimally involved in avian reproductive function. UVA and UVB have anti-rachitic properties which catalyse the synthesis of vitamin D3 from 7-dehydroxycholesterol in the skin of feet and legs, a function that prevents rickets, minimises the incidence of tibial dyschondroplasia, and normalises growth and bone ash in young birds fed diets deficient in vitamin D3; surprisingly, there is sufficient UVA in white fluorescent light to produce these benefits. UVC from the sun is filtered out by the atmosphere's ozone layer, so does not occur in sunlight, but artificially produced UVC has germicidal properties and has been shown to protect domestic fowl from aerogenic viral infections, however, vaccination has made this property superfluous to the modern poultry industry. Recently, the introduction of lamps that emit both visible light and UV has made the provision of UVA to poultry a practical proposition, and so it is opportune that the responses of poultry to UV radiation are reviewed and its relevance to modern poultry production assessed.
(Received January 21 2009)
(Accepted April 10 2009)