Photoperiod during incubation affects hatching performance, leg bone development and key gene expression in
1Institute of Animal Husbandry and Veterinary Medicine, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, PR China; College of Animal Science and Technology, Hebei Agricultural University, Baoding Hebei 071001, PR China.
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.
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