Cecal microbiota and metabolomic profiles associated with residual feed intake divergence in laying ducks.

Feed efficiency is an important determinant of productivity in laying ducks, but the cecal microbiota and metabolomic profiles associated with residual feed intake (RFI) divergence remain unclear. In this study, 767 laying ducks were phenotyped for RFI, and cecal samples from low-RFI (LRFI) and high-RFI (HRFI) ducks (n = 20 per group) were subjected to 16S rRNA gene sequencing and LC-MS-based untargeted metabolomics. LRFI ducks consumed 25.5% less feed and showed lower RFI and feed conversion ratio than HRFI ducks; however, they also exhibited higher average daily egg mass and egg production rate, whereas body weight-related traits did not differ between groups. Cecal microbiota composition and overall metabolomic profiles differed clearly between LRFI and HRFI ducks. At the genus level, Phocaeicola and Olsenella were enriched in LRFI ducks, and 251 differential metabolites with varying annotation-confidence levels were detected between groups. Pathway analysis descriptively indicated recurring themes related to lipid metabolism and bile acid/steroid-associated metabolism, although no KEGG pathway remained significant after multiple-testing correction. Integrated analysis further showed exploratory correlation patterns among differential genera, metabolites, feed-efficiency-related traits, and laying-performance traits. These findings identify cecal microbial and metabolic features associated with the overall LRFI-HRFI phenotypic contrast and provide a basis for targeted validation in larger laying-duck populations.