Quercetin and Ligilactobacillus salivarius alleviate fatty liver syndrome in layers via modulating gut microbiota and hepatic lipid metabolism.

Fatty liver hemorrhagic syndrome (FLHS) in laying hens is closely associated with gut microbiota dysbiosis and lipid metabolism disorder; however, there is limited evidence regarding the combined effects of quercetin and Ligilactobacillus salivarius (L. salivarius) on lipid metabolism in laying hens. Ninety-six healthy 50-week-old laying hens were randomly allocated to four treatments: a basal diet (CON), a high-energy low-protein diet as the fatty liver model treatment (HELP), the HELP diet with 0.2 g/kg quercetin plus 5 × 10⁷ CFU/kg L. salivarius(LD), or the HELP diet with 0.4 g/kg quercetin plus 1 × 10⁸ CFU/kg L. salivarius(HD). Dietary supplementation with quercetin and L. salivarius significantly mitigated the HELP diet-induced decline in laying rate and increase in feed-to-egg ratio, and attenuated increases in liver index, abdominal fat ratio, and serum triglyceride and total cholesterol levels (P < 0.05). In the ileum, the HD diet reduced the HELP diet-enriched taxa-Rothia, Clostridium sensu stricto 1, and Lachnospiraceae NK4A136 group (P < 0.05). Notably, Turicibacter, Bacillus, Ligilactobacillus, HT002, Bacteroides and Akkermansia were enriched in the HD group (P < 0.05). Liver transcriptomic data showed that the HD diet significantly enriched pathways related to lipid and energy metabolism, including PPAR signaling pathway, propanoate metabolism, carbon metabolism, oxidative phosphorylation, fatty acid degradation, and primary bile acid biosynthesis pathways. Correlation analysis further linked HD-enriched genera, including Akkermansia and Bacteroides with key hepatic genes involved in fatty acid degradation, PPAR signaling pathway, and carbon metabolism (P < 0.05). Overall, combined quercetin and L. salivarius supplementation effectively alleviated fatty liver in laying hens, potentially through modulation of the ileal microbiota and the activation of hepatic lipid catabolic processes.