Effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens.

ABSTRACT

1. The effects of photoperiod on broodiness, egg-laying and endocrine responses in native laying hens were investigated. A total of 648, 18-week-old native laying hens (Beijing You Chicken, BYC) were randomly allocated to 6 groups with 3 replicates. The birds were exposed to 1 of 6 different photoperiods, including 16L8D (0600 to 2200 h) for group 1; 12L2D4L6D for group 2; 8L4D4L8D for group 3; 16L8D (0300 to 1900 h) for group 4; 14L10D for group 5; and 18L6D for group 6. 2. The broodiness rate and egg-laying rate for weeks 20-26, 27-33, 34-40, 41-47, 48-54 and 55-61 were calculated, and serum prolactin (PRL), luteinising hormone (LH), 17-beta-oestradiol (E2), melatonin (Mel) and progesterone (P4) concentrations were measured at the end of each stage. 3. Significant effects were observed on the rate of broodiness by the photoperiod and stage, but the interaction of photoperiod and stage was not significant. The rate of broodiness for group 3 (5.9%) was significantly higher than other groups, with group 2 being the lowest (2.8%). Broodiness rate was the highest for weeks 41-47 (9.9%). Significant effects were observed on average egg-laying rate by photoperiod and stage the rate of egg-laying of groups 2 and 5 were significantly higher than groups 1, 4 and 6. 4. There were no significant effects of photoperiod on PRL, LH and Mel concentrations at 26, 33, 40 and 54 weeks of age (P > 0.05), but at 47 weeks of age, PRL and LH concentrations of group 1 were significantly lower than those in other groups. 5. The study suggests that the photoperiod of group 2 (12L2D4L6D) is optimal for the birds' performance to give the lowest broodiness rate and the highest egg-laying rate during the whole laying period, and 41-47 weeks may be a key stage for the photomodulation of broodiness.