The differences of gonadal hormones and uterine transcriptome during shell calcification of hens laying hard or weak-shelled eggs.

Our study concluded that mammillary thickness and mammillary knob width of the HS were significantly lower than LS. P4 and 1,25-(OH)2D3 were significantly higher in the initiation period of HS. They may impact initial calcification when the mammillary layer is formed. The initiation period of calcification determined eggshell strength rather than the growth or termination periods. We inferred P4 or 1,25-(OH)2D3 may effect the ultrastructure of the mammillary layer by regulating the expression of uterine genes.