Eggshell depigmentation in the late phase of production is associated with altered Microbiota and Metabolism of the uterus in laying hens

The significant depigmentation of brown eggshells occurs in the in the late-phase laying hens, which directly affects consumer acceptance. However, the biological mechanism of eggshell depigmentation based on uterine metabolism has not been elucidated. In this study, a total of 4 group were as follows: 1) 65-week-old laying hens with normal color; 2) 65-week-old laying hens with light color; 3) 80-week-old laying hens with normal color; 4) 80-week-old laying hens with light color. Variations in the pigment contents, uterine antioxidant capacity, uterine microbiota, and uterine metabolomics were examined in current study. Results showed that significantly decreased L* values and increased a* and b* values were observed in the depigmentation group (P < 0.05). The protoporphyrin IX content of the uterus with eggshell depigmentation was significantly decreased in 65-week-old laying hens (P < 0.05). Uterine MDA content was significantly increased in the depigmentation groups at 65 and 80 weeks of age, accompanied by reduced SOD and increased IgA levels (P > 0.05). The abundance of Proteobacteria and Campilobacterota was markedly reduced in the uterus with eggshell depigmentation, whereas Firmicutes was elevated at 65 weeks of age (P < 0.05). Further, Psychrobacte as biomarkers can accurately distinguish between normal color and depigmentation in eggshells (AUC = 0.91). A total of 51 differential metabolites were significantly enriched in the down-regulated sphingolipid metabolism, linoleic acid metabolism, citrate cycle, oxidative phosphorylation, PPAR signaling pathway, FoxO signaling pathway, and apoptosis at 65 weeks of age (P < 0.05). Meanwhile, there were 82 differential metabolites were significantly up-regulated at 80 weeks of age, which mainly enriched in up-regulated linoleic acid metabolism, purine metabolism, and pentose phosphate pathway (P < 0.05). These findings elucidate the specific metabolic mechanisms responsible for eggshell depigmentation in 65- and 80-week-old laying hens, contributing to the improvement of eggshell depigmentation by the precise nutritional modulation in the late-phase laying hens.