摘要Background The decline in reproductive performance of aged hens is mainly attributed to oxidative damage in reproductive organs,hepatic lipid metabolism disorders,and intestinal microbiota dysbiosis.Glycyrrhizin(GL)has been proven to enhance antioxidant capacity,regulate lipid metabolism and gut microbiota in mammals,but its efficacy in hens remains unclear.Hence,this study aimed to investigate whether dietary GL supplementation improves reproductive performance in hens during the late laying stage by modulating intestinal microbiota compo-sition,hepatic lipid metabolism and ovarian antioxidant status.Results Dietary supplementation with 100 mg/kg GL significantly improved the egg production rate,egg qual-ity,and hatching rate in aged breeder hens(P＜0.05).GL supplementation also increased the serum levels of HDL-C,TP and ALB,and enhanced the antioxidant capacity in both serum and ovary(P＜0.05).In addition,dietary GL elevated the serum progesterone(P4)levels by enhancing the transcription level of steroid synthesis key enzymes(CYP11A1 and 3β-HSD)in the ovary(P＜0.05).Dietary GL also promoted the synthesis and transport of vitellogenin(VTG)by upregulating the VTG-Ⅱ(P＜0.05)and APOV1(P=0.077)expression levels in the liver,thereby increasing the number of grade follicles and small yellow follicles.Moreover,dietary GL enhanced hepatic fatty acid β-oxidation by upregulating PPARα and CPT-I(P＜0.05),and downregulating ACC expression levels(P＜0.05).In agreement,liver metabolomics analysis revealed that dietary GL supplementation significantly altered hepatic metabolism,with 389 differentially identified metabolites(P＜0.05).The key metabolites(e.g.,taurocholic acid,tauroursodeoxycholic acid,nicotinuric acid,glycodeoxycholic acid(hydrate))were identified,and they were mainly functionally enriched in beta-alanine metabolism nicotinate,taurine and hypotaurine metabolism(P＜0.05).Finally,16S rRNA gene sequencing revealed that dietary GL reversed age-induced changes in gut microbiota composition,characterized by a significant increase in Lactobacillus abundance and a decrease in Bacteroides(P＜0.05).Conclusions These results collectively demonstrate that dietary supplementation with 100 mg/kg GL improved reproductive performance by reversing age-induced changes in gut microbiota,enhancing hepatic vitellogenin synthesis,and ameliorating ovarian function in aged breeder hens.This study suggests that dietary GL is a potential strategy to improve reproductive performance in broiler breeder hens during the late laying period.