Microbiota contributes to regulates the external genitalia development through gut-testis axis in male geese.

Geese is one of the few poultry species with complete external genitalia, and the external genitalia abnormal development has become an important factor limiting the reproductive efficiency of the goose industry. Recent studies have shown that the gut microbiota plays an important role in regulating male reproductive processes, but its regulatory mechanisms in male geese's external genitalia development remain unclear. In this study, male geese with normal development (ND) and abnormal development (AD) external genitalia were selected as the research object, and multi-omics were used to investigate the regulatory of the microbe-mediated gut-testis axis on external genitalia development. At the transcriptomic level, we identified key DEGs (KNG1, P2RY4, SSTR5, and HRH3) in the testis and external genitalia between ND and AD groups, which were significantly enriched in the neuroactive ligand-receptor interaction pathway. Metabolomics analysis revealed that DMs in the ND and AD groups were significantly enriched in pathways related to aromatic amino acid metabolism and neural signal transduction. Furthermore, metagenomic results showed that the ND group was identified key bacterial genera g_Blautia and g_Faecousia affecting external genitalia development, which were associated with SCFAs synthesis and neuroendocrine signaling regulation. Integrated with multi-omics data, it was revealed that gut-derived neuroactive metabolic signals may participate in the molecular regulation of external genitalia development in male goose by modulating GPCRs signaling. Our findings not only provide new insights into the gut-testis axis regulates the development of external genitalia in male geese, but also contribute to improving the reproductive performance of male geese.