The combined supplementation of quercetin and Ligilactobacillus salivarius improves production performance, lipid metabolism, and ileal health in late-phase laying hens.

We studied the effects of a combination of quercetin and Ligilactobacillus salivarius (L. salivarius) on production performance, lipid metabolism, and ileal health in late-phase laying hens. In a 12-week feeding trial, 480 healthy 50-week-old laying hens received a basal diet supplemented with various treatments: 0 (CON), 0.2 g/kg quercetin and 0.5 × 10(8) CFU/kg L. salivarius (LD), double dose of group LD (MD), triple dose of group LD (HD), and 1.46 g/kg quercetin microcapsules (0.4 g/kg quercetin content matching the group MD) and 1 × 10(8) CFU/kg L. salivarius (group BM). Results showed that the laying rate was significantly higher, feed-to-egg ratio was significantly lower with supplementation (P < 0.05), with no changes in egg quality. Supplementation reduced serum TG, TC, HDL-C, and LDL-C levels, along with a significant reduction in the abdominal fat ratio (P < 0.05). Compared with the CON group, the HD and BM groups had lower TG and TC levels and reduced expression levels of ACC-α and SREBP1 in the liver (P < 0.05). In the ileum, the MD, HD, and BM groups also showed, reduced V/C ratios and histopathological scores (P < 0.05), increased intestinal barrier gene expression, including occludin, claudin-1, Muc2, and ZO-1 (P < 0.05), and higher expression levels of IL-10 and IL-4 (P < 0.05), alongside lower expression levels of IL-6 and IL-2 (P < 0.05). Additionally, dietary supplementation with quercetin and L. salivarius increased the abundance of Lactobacillales and Ligilactobacillus. Overall, the combination of quercetin and L. salivarius improved laying rate while reducing feed-to-egg ratio and abdominal fat ratio, likely mediated by enhanced hepatic lipid metabolism and improved gut immune status. These findings provide novel insights into the combined supplemation for enhancing poultry production efficiency.