# Investigation of Mechanism of Small Peptide Application in Enhancing Laying Performance of Late-Laying Hens Through Bidirectional Liver–Gut Interactions

## TL;DR

Small peptides improve egg quality in older hens by boosting gut health and liver function.

## Contribution

This study reveals how small peptides enhance egg quality in late-laying hens via gut-liver interactions.

## Key findings

- Small peptides increased eggshell strength and albumen quality in late-laying hens.
- Peptides improved antioxidant activity and gut microbiota diversity in hens.
- Hepatic gene expression changes linked to steroid synthesis were observed with peptide supplementation.

## Abstract

Improving egg quality in aging hens is crucial for sustainable farming. This study found that dietary small peptides enhanced eggshell strength and albumen quality in late-laying hens. This improvement was linked to better antioxidant status, immunity, increased beneficial gut bacteria, and altered liver gene activity related to steroid synthesis. Small peptides show promise as a dietary strategy to maintain egg quality in older hens.

The primary objective of this study was to investigate the mechanism through which small peptides regulate the productive performance and egg quality of laying hens during the late-laying period. A total of 200 Lohmann Pink laying hens, aged 400 days, were randomly assigned into a control treatment (CON) and a small peptide treatment (SP) for a 120-day treating period. Productive performance, egg quality, serum antioxidant capacity, intestinal morphology, microbial community, and hepatic gene expressions were measured. Results showed that SP supplementation significantly increased eggshell strength and albumen height, while reducing the rate of abnormal eggs (p < 0.05). SP notably enhanced the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and hepatic lipase (p < 0.05). Additionally, SP supplementation significantly increased microbial α-diversity (p < 0.05) and elevated the relative abundances of Ruminococcus, Lactobacillus, and Faecalibacterium (p < 0.05). Hepatic transcriptomic analysis revealed that up-regulated genes in the SP treatment were primarily enriched in steroid biosynthesis, while down-regulated genes were mainly associated with the Yersinia infection pathway. In conclusion, small peptide supplementation efficiently improved eggshell strength and albumen height while reducing the rate of abnormal eggs by modulating the interactions between gut microbiota and hepatic gene expressions. Our findings may provide an effective option for enhancing egg quality in the late-laying period.