title: Photoperiodic regulation of plasma melatonin levels in the laying chicken (Gallus domesticus)1.
abstract: Plasma melatonin profiles were determined in laying chickens maintained on either a 16L:8D or a 20L:4D light-dark cycle (LDC). The range of plasma melatonin concentrations was low during the light period (40-100 pg/ml) and higher during the dark period (150-390 pg/ml). Compared to the light period, plasma concentrations of melatonin were 4- to 5-fold higher (P less than 0.05) during the dark period. The amplitude of melatonin concentrations was greater when hens were held under a short dark period (4.6-fold, 20L:4D) than when hens were exposed to a 16L:8D LDC (3.8-fold). In the laying chicken, a broad peak in concentration of plasma melatonin was found in the dark period. It was different from that previously reported in the chick. Since the time of oviposition in the hen occurs in a limited period after the onset of darkness in a LDC, a modified physiological function of melatonin for birds of different ages may account for the difference in the nocturnal pattern of plasma melatonin. The elevated level of plasma melatonin in the dark period of a LDC is considered to be essential for regulating the time of oviposition in the laying chicken under a particular LDC.
mesh_terms: D000818:Animals; D002645:Chickens / Q000502:physiology*; D005260:Female; D008027:Light; D008550:Melatonin / Q000097:blood*; D010058:Oviposition; D010507:Periodicity
chemical_list: D008550:Melatonin