Eggshell Biomineralization and Genetic Regulation of Eggshell Strength of Laying Hens

Eggshell quality profoundly affects egg commercial value, storage performance and food safety, and its late-period deterioration restricts the sustainable production of long-cycle laying hens. With the poultry industry extending the laying cycle to 100 weeks for the “500 eggs within 700 days” production target, hens suffer severe shell quality degradation after 60 weeks of age, with the eggshell breakage rate rising from 1–2% to 5–8% and resulting in considerable economic losses. Eggshell strength is a moderately heritable polygenic trait determined by delicate biomineralization and ultrastructural organization. Specific functional genes dominate shell mineralization by regulating uterine calcium homeostasis, crystal nucleation and structural assembly. Notably, prominent genotype–age interactions reduce heritability in aged hens, and most identified genetic loci fail to maintain stable late-phase shell quality. Uterine epithelial aging triggers ultrastructural abnormalities, including thickened mammillary layers, reduced palisade layers and disordered pores, impairing shell mechanical resistance and gas exchange. Single-cell multi-omics technologies enable high-resolution profiling of uterine cellular heterogeneity and mineralization-related signaling networks, providing novel approaches to decipher the molecular mechanisms of shell quality decline. This review summarizes eggshell biomineralization, genetic regulation, age-dependent quality deterioration and advanced omics applications, aiming to offer theoretical references for improving late-stage eggshell quality and breeding elite laying hen strains.