Ultraviolet radiation and laying pullets

1. Responses to ultraviolet (UV) radiation were studied in two trials. In o ne trial, sexually mature pullets, that had been maintained on an 8L:16D re gimen from 2 d of age, were exposed sequentially, for periods of 9 to 12 d, to a further 8 h of very dim visible light LDV, to 8 h of UV radiation and , finally, to an extra 8 h of normal light (conventional 16L:8D). Individua l ovipositions were recorded during the last 48 h of each treatment. In the second trial, sexually mature pullets which had been allowed to 'free-run' for 14 d under continuous normal illumination (LL), were given, in additio n to the normal light, a 12-h period of UV radiation commencing at midday o r midnight for a further 15 d. During the final 1 8 h oviposition times wer e recorded and 1 food intakes for each 12-h period were determined. 2. In trial 1, mean oviposition time under VDV and UV supplementation was n ot significantly different from that under the 8L:16D regimen. Transfer to a 16L:8D regimen altered mean time of oviposition by about 4 h. In trial 2, eggs continued to be laid almost at random in all groups. 3. Food intake was suppressed during the 12-h period of UV supplementation compared with that when the birds were not receiving UV. 4. It is concluded that the addition of 8 h of UV radiation (at the intensi ty used in these studies) to 8 h of normal light does not cause a phase shi ft in the timing of the 'open-period' for pre-ovulatory luteinising hormone release which determines the time of oviposition. Furthermore, the inserti on of 12-h periods of UV into continuous illumination does not entrain egg laying. 5. The suppressing effect of UV on food intake but lack of influence on the timing of the ovulatory cycle suggests that UV (at the intensity used in t his study) acts principally at the retinal level and, as a result, stimulat es only behavioural responses in laying birds.