Photoperiod affects the laying performance of the mountain duck by regulating endocrine hormones and gene expression.

Light mainly affects animal reproductive performance through the hypothalamus- pituitary-gonadal axis, but the specific regulating mechanism is not yet clear in duck. To reveal the effects of light on the laying performance of ducks and its possible regulatory mechanisms, Shanma ducks at 52 weeks age were divided into three group treated with different photoperiods of 16 hr (control group), 24 hr (long-photoperiod group, LP), and 8 hr (short-photoperiod group, SP). Laying performance, endocrine-related hormones and gene expression of three groups were compared. The results showed that laying performance was greatest in the LP group; including laying rate, average egg weight and feed-egg ratio. Compared to the SP group, GnIH plasma concentration was decreased in the LP group, whilst FSH was increased in the LP group. GnIHR gene expression in the pituitary and large yellow follicles were downregulated in the LP group. The expression of Mel-a in large white follicles, and Mel-b and Mel-c in the hypothalamus were also downregulated in the LP group. Altogether these results suggest that extended photoperiods may promote the laying performance of ducks by inhibiting the secretion of GnIH and the expression of GnIHR and melatonin receptor genes.