Gut microbiota modulation by novel synbiotic improves production performance and ovarian function in aged laying hens via gut-ovary axis

The management of oxidative stress and ovarian dysfunction associated with aged laying hens, which is highly involved in gut microbiota, has been suggested as a feasible approach to improve production performance. Here, we investigated the effects of a novel synbiotic (Bacillus amyloliquefaciens + inulin, BAI), a gut microbiota regulator, on the improvement of production performance in aged laying hens, and dissected the underlying mechanisms using multi-omics analysis. Our findings showed that, compared to the control, high-dosage BAI supplementation significantly improved production performance; enhanced intestinal health, evidenced by the increase of villus height (p < 0.01), the expression of gut barrier-related genes (Claudin-1 and Claudin-2) (all p < 0.001), and immune levels (SIgA and IFN-γ) (all p < 0.01); meliorated ovarian function, confirmed by reduced oxidative stress (p < 0.001) and pathological lesions, as well as increased follicle numbers (p < 0.01 or p < 0.001), serum contents of reproductive hormone (estrogen, luteinizing hormone, and follicle-stimulating hormone) (p < 0.05 or p < 0.001), and the mRNA levels of yolk precursor synthesis-associated genes (APOVLDL-Ⅱ, VTG-Ⅱ, and VLDLR) (all p < 0.001). The 16S rRNA sequencing showed that BAI augmented the relative amount of Lactobacillus, Akkermansia, and Bacteroides and other short-chain fatty acids (SCFAs)-producers. Blood metabolome analysis demonstrated that the predominant metabolites changed by BAI were principally involved in SCFA metabolism, steroid hormone biosynthesis, steroid biosynthesis, and intestinal immune network for IgA production. Ovarian transcriptome analysis indicated that BAI significantly inhibited pathways of ferroptosis and peroxisome, confirmed by RT-qPCR. Furthermore, fecal microbiota transplantation (FMT) from BAI-treated aged hens improved production performance, ovarian function, and oxidative stress status in antibiotic-administrated hens. In sum, our study uncovers that BAI improves production performance and ovarian dysfunction via gut microbiota in aged laying hens. Thus, modulating gut microbiome is an effective approach to laying rate reduction of aged hens.