Effect of photoperiod on performance, ovarian morphology, reproductive hormone level, and hormone receptor mRNA expression in laying ducks

ABSTRACT We investigated the effect of photoperiod on performance, ovarian morphology, reproductive hormones levels and their receptors mRNA expressions in laying ducks. After adaption, 300 252-d-old Jinding laying ducks were randomly allocated to 5 groups, receiving 12L (hours of light):12D (hours of darkness), 14L:10D, 16L:8D, 18L:6D or 20L:4D, respectively. Each treatment had 6 replicates of 10 birds each. The feeding trial lasted 8 wks. Egg production, egg mass and average daily feed intake increased linearly and quadratically with increasing photoperiods (P ˂ 0.05), and the higher values of them occurred in photoperiods ≥ 16 h, compared with 12L:12D (P ˃ 0.05). Initial and bare stroma weight increased quadratically, while total large white follicles (LWFs) number and weight increased linearly and quadratically, with increasing photoperiods (P ˂ 0.05). The higher values of them occurred in 16L:8D and 18L:6D treatments as well as the higher total LWFs weight also occurred in 20L:4D, compared with 12L:12D (P ˃ 0.05). Besides, 16.93 and 16.93 h were the optimal photoperiods for bare stroma (follicles ≥ 2 mm in diameter removed) weight and total LWFs weight respectively, calculated from reliable regression equations (R2 ≥ 0.5071). Compared with 12L:12D, the higher levels of estradiol, progesterone, follicle-stimulating hormone (FSH) as well as the higher expressions of estrogen, luteinizing hormone (LH) and progesterone receptors were observed in ≥ 16 h photoperiods (P ˂ 0.05), while the higher LH level and FSH receptor expression only occurred in 16L:8D and 18L:6D (P ˂ 0.05). In the hypothalamus, higher mRNA expression of gonadotropin-releasing hormone occurred in 16L:8D and 18L:6D groups (P ˂ 0.05). Meanwhile, gonadotropin-inhibitory hormone and prolactin increased in 20-h photoperiod (P ˂ 0.05), and the latter may be due to the up-regulation of vasoactive intestinal peptide expression (P ˂ 0.05). To sum up, an appropriate photoperiod could improve the performance, reproductive organs and ovarian follicles development through reproductive hormones and their receptors, and 16.56-10.93 h is an adequate photoperiod for laying ducks.