Quercetin-based treatment improves eggshell quality in aged laying hens by modulating immune response, eggshell gland health and serum metabolome.

Background: Eggshell quality is a critical determinant of egg product value and consumer preference. Deficient eggshells increase breakage susceptibility, leading to economic losses and reduced marketability. Dietary interventions hold promise for improving eggshell quality. Quercetin, a naturally occurring flavonoid, exhibits diverse biological activities relevant to eggshell formation. These include antioxidant and anti-inflammatory properties, and potential modulation of estrogen levels, which are known to influence eggshell quality.

Results: A total of 160 46-week-old laying hens were randomly divided into two groups, with 8 replicates in each group and 10 chickens in each replicate. The control group was fed a corn-soybean meal basal diet, while the experimental group received a basal diet supplemented with 300 mg kg^-1 quercetin. The trial period lasted for 10 weeks. The study showed that dietary supplementation with quercetin significantly increased eggshell thickness (P < 0.001). Eggshell ultrastructure analysis revealed significant increases in effective layer thickness (P < 0.001) and a marked decrease in the thickness ratio of the mammillary layer to total eggshell thickness (P < 0.001) with quercetin supplementation. Serum analysis indicated significantly higher levels of immunoglobulin A, immunoglobulin G, estrogen receptors and carbonic anhydrase-2 in hens supplemented with quercetin compared to controls (P < 0.05). Furthermore, quercetin supplementation reduced tubular gland edema and improved villus height, luminal epithelial cell height and gland duct diameter (P < 0.05). Quantitative real-time PCR analysis showed that quercetin supplementation altered immune responses in the liver, spleen and oviduct. Notably, quercetin supplementation increased metabolites associated with glycine, serine and threonine metabolism. These amino acids, key precursors of eggshell matrix proteins, showed increased metabolism, suggesting a potential mechanism by which quercetin supports eggshell biomineralization.

Conclusion: This study suggests that compromised eggshell quality might be associated with impaired biomineralization function in the eggshell gland, potentially due to tissue damage. Conversely, dietary quercetin supplementation significantly increased eggshell thickness. We propose a potential mechanism involving the activation of glycine, serine and threonine metabolic pathways, which might enhance the biomineralization capacity and overall health of the eggshell gland. © 2025 Society of Chemical Industry.