Abstract
The decline in eggshell quality resulting from aging hens poses a threat to the financial benefits of the egg industry. The deterioration of eggshell quality with age can be attributed to changes in its ultrastructure and chemical composition. Specific matrix proteins in eggshells have a role in controlling crystal growth and regulating structural organization. However, the variations in ultrastructure and organic matrix of eggshells in aging hens remain poorly understood. This study assessed the physical traits, mechanical quality, chemical content, as well as the microstructural and nanostructural properties of eggs from Jing Tint 6 hens at 38, 58, 78, and 108 wk of age. Subsequently, a quantitative proteomic analysis was conducted to identify differences in protein abundance in eggshells between the ages of 38 and 108 wk. The results indicated a notable decline in shell thickness, breaking strength, index, fracture toughness, and stiffness in the 108-wk-age group compared to the other groups (P < 0.05). The ultrastructure variations primarily involved an increased ratio of the mammillary layer and a reduced thickness of the effective layer of eggshell in the 108-wk-age group (P < 0.05). However, no significant differences in eggshell compositions were observed among the various age groups (P > 0.05). Proteomic analysis revealed the identification of 76 differentially expressed proteins (DEPs) in the eggshells of the 38-wk-age group and 108-wk-age group, which comprised proteins associated with biomineralization, calcium ion binding, immunity, as well as protein synthesis and folding. The downregulation of ovocleidin-116, osteopontin, and calcium-ion-related proteins, together with the upregulation of ovalbumin, lysozyme C, and antimicrobial proteins, has the potential to influence the structural organization of the eggshell. Therefore, the deterioration of eggshell quality with age may be attributed to the alterations in ultrastructure and the abundance of matrix proteins.