Integrative multi-omics analyses reveal the molecular mechanisms of lysozyme in alleviating hepatic lipid accumulation in post-peak laying quail

Lysozyme is a natural antimicrobial protein increasingly used as an antibiotic alternative in animal husbandry. However, its role in hepatic lipid metabolism, especially in post-peak laying poultry, is not well understood. This study employed a multi-omics approach to investigate the hepatic responses in late-laying quails supplemented with lysozyme (500 mg/kg diet) for 8 weeks compared to a control group. Lysozyme supplementation significantly increased average egg weight during week 1∼4 (P < 0.01). At the end of the trial, it significantly reduced hepatic lipid droplet area and triglyceride content (P < 0.05). Multi-omics analysis revealed that these improvements were linked to a coordinated alleviation of endoplasmic reticulum (ER) stress and reductions in lipotoxic metabolites, despite no observed effects on gut morphology. Specifically, lysozyme downregulated key ER stress-related genes, including protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic translation initiation factor 2 alpha (EIF2α), and activating transcription factor 4 (ATF4) (P < 0.05), as well as lipogenic genes such as fatty acid synthase (FASN) and acetyl-CoA carboxylase 1 (ACC1) (P < 0.01). It also decreased hepatic sphingoid bases and saturated fatty acids (P < 0.05), contributing to reduced lipogenesis and hepatocyte apoptosis (P < 0.05). Although 16S rRNA sequencing revealed no shifts in overall α- or β-diversity, lysozyme induced specific taxa changes which characterized by increasedabundances of Bacteroides gallinaceum and Olsenella spp., alongside reduced levels of Subdoligranulum and RF39-related bacteria. Mantel correlation analysis further indicated species-specific associations between these microbial changes and host ER stress and lipid metabolism parameters, implicating gut microbiota-mediated modulation of hepatic responses. In summary, these findings demonstrate that dietary lysozyme mitigates hepatic steatosis in post-peak laying quails through coordinated suppression of ER stress and lipogenesis, alongside concurrent specific gut microbial alteration.