Özet:

: Circadian rhythms affect the physiology and behavior of most organisms. The ovulation–laying cycle of poultry exhibits evident rhythmic patterns. However, the underlying biological mechanism has remained unclear. Herein, Yangzhou goose ( Anser cygnoides) were selected at 6:00, 12:00, 18:00, and 24:00 ( n = 6/timepoint) to investigate the regulation of circadian egg-laying through the light-driven melatonin secretion. Our study revealed that the laying rates displayed diurnal fluctuations, with a peak of 40% of eggs being laid between 4:00 and 7:00. The cosine analysis revealed that the expression of clock genes exhibited rhythmicities ( p < 0.05). Relevantly, melatonin secretion also displayed circadian rhythmicity and sharply decreases with increasing amount of light ( p < 0.001). The immunohistochemical analysis found that the melatonin receptor is highly expressed during the night period. Notably, tissue distribution analysis further revealed that the melatonin receptor genes showed a decreasing trend in the pineal gland and hypothalamic–pituitary–gonad (HPG) axis throughout the day. Concomitantly, the expression of reproduction-related genes at 12:00 was significantly higher than that at 24:00 ( p < 0.01). Taken together, these data suggested cyclical secretion of melatonin in response to photoperiod, which acts as a neuroendocrine transducer of circadian rhythm and the time preference of reproduction in domestic geese.

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