Abstract
This paper aimed to study the effects of photoperiod during incubation on hatching performance, embryonic leg bone development and metabolism, and key gene expression in melanopsin mediated PLC-PKC pathway in Beijing You Chicken (BYC). A total of 1,408 eggs from 32-wk-old BYC breeders were randomly divided into four light incubation groups: Inc8L:16D (6:00-14:00), Inc12L:12D (6:00-18:00), Inc16L:8D (6:00-22:00), and Inc24D (24 h darkness). Each group contained 352 eggs with 4 replicate trays of 88 eggs each. The leg bone development and metabolism, and key gene expressions including Protein Kinase C (PKC), Phospholipase C Beta 1 (PLCβ1), Diacylglycerol Kinase (DGK), and Transient Receptor Potential Canonical 6/7 (TRPC6/7) in melanopsin mediated PLC-PKC pathway were determined at embryonic day 8, 11, 14, 17, 20 (E8, E11, E14, E17, E20). The hatching performance at day 1 and the gait score of chickens at day 1, 7, 21 and 42 were assessed. Results showed that Inc8L:16D increased hatch weight (P < 0.05), and enhanced femur, tibia, third toe length and femur width at E11 (P < 0.05). The Inc12L:12D increased tibia length (P < 0.05), and Inc16L:8D improved metatarsal length (P < 0.05) at E11. At E14, Inc8L:16D increased femur and metatarsal lengths compared to Inc24D (P < 0.05). By E17, Inc12L:12D exhibited greater femur length, while Inc8L:16D showed increased tibia length, femur width, and tibia width (P < 0.05). The Inc12L:12D decreased gait scores at day 7 and 21 (P < 0.05). The Inc12L:12D and Inc18L:6D had higher BAP level at E14 (P < 0.05), and Inc12L:12D had significantly higher bone-specific alkaline phosphatase (BAP) level at E20 (P < 0.01). The Inc16L:8D and Inc24D had higher (P < 0.05) or significantly higher (P < 0.01) TRAP-5b and β-CTx at E11. The Inc24D had significantly higher β-CTx (P < 0.01) at E17. The Inc24D had significantly higher parathyroid hormone (PTH) level at E11 (P < 0.01) and higher level at E17 (P < 0.05). Melanopsin gene (OPN4) expression was increased in Inc8L:16D at E14 (P < 0.05). The Inc12L:12D increased PLCβ1, DGK, PKC expression (P < 0.05) at E11 and E14. The Inc8L:16D upregulated PLCβ1, DGK, PKC and TRPC6/7 at E11 (P < 0.05), while Inc12L:12D elevated TRPC6/7 expression. The Inc12L:12D upregulated TRPC7 expression at E8 compared to Inc16L:8D (P < 0.05). At E17, Inc12L:12D enhanced PLCβ1 and PKC expression (P < 0.05). This study suggested that photoperiod during incubation affected embryonic and post-hatch bone development over time, especially Inc8L:16D and Inc12L:12D. The Inc8L:16D group exhibited a higher hatch weight, while the Inc12L:12D group showed lower gait scores (better leg quality). The Inc16L:8D may suppress melatonin secretion of embryos and bring negative effects. The Inc12L:12D reduces osteoclast-related enzyme secretion, which may be related with its increased PLCβ1, DGK and PKC expression, elevated TRPC6/7 expression in melanopsin mediated PLC-PKC pathway.