Microbiome and metabolome changes in laying hens induced by dietary epsilon-polylysine

Epsilon-polylysine (ε-PL) is a natural antimicrobial peptide that has been broadly applied in the food industry as a preservative. The effects of ε-PL on the intestinal microbiota, animal metabolism, and its potential as a "new feed additive" require further exploration. In this study, ninety Hy-Line Brown laying hens were randomly divided into three groups. Egg-laying performance, egg quality, and liver parameters were measured; expression of gut barrier, immunity, and ferroptosis related genes in each intestinal segment were detected; microbiome and metabolomic analyses were performed. The results demonstrated that dietary ε-PL supplementation significantly increased average egg weight and egg quality (P < 0.05). It also markedly, ε-PL supplementation significantly increased the villus height to crypt depth ratio in the duodenum and ileum (P < 0.01), significantly reduced the mRNA levels of interleukin-1 beta (IL-1β) and interleukin-6 (IL-6), and elevated the mRNA levels of interleukin-10 (IL-10) and tumor necrosis factor-alpha (TNF-α) in the intestine (P < 0.05). Moreover, ε-PL inhibited intestinal mucosal ferroptosis (P < 0.05) and mitigated severe fatty liver development, as evidenced by a significantly reduction in hepatic malondialdehyde (MDA) content (P < 0.01). Microbiota analysis revealed that ε-PL supplementation significantly increased the abundance of Lactobacillus and Saccharimonadales; while decreasing the abundance of Anaerotruncus and Slackia in the cecal microbiota. Additionally, ε-PL supplementation enhanced the amino acid metabolism, lipid metabolism, the digestive system, arginine biosynthesis, tryptophan metabolism, bile secretion, and steroid hormone biosynthesis in the intestine, which might contribute to improved egg quality and intestinal absorptive capacity, as well as the inhibition of fatty liver formation. In summary, dietary ε-PL supplementation exerts multiple beneficial effects in laying hens, including enhancing egg quality, alleviate inflammation, boosting antioxidant capacity, improving intestinal morphology, modulating gut microbiota, and protecting liver health.