Multi-omics analysis of cecal microbiota-hypothalamus axis interactions in small-sized meat ducks with divergent residual feed intake.

Residual feed intake (RFI) is an indicator of feed efficiency that reflects variation in nutrient utilization independent of growth. This study characterized physiological traits and multi-omics profiles associated with divergent RFI in small-sized meat ducks. From an initial population of 500 1-day-old ducks, a total of 420 healthy ducks were individually housed from 21 to 42 d to record feed intake, and ducks with low RFI (LRFI) and high RFI (HRFI) were identified for further analyses. During the experiment, 30 ducks per group for growth performance, 15 ducks per group for plasma biochemical and 5 per group for multi-omics. Compared with HRFI ducks, LRFI ducks showed lower feed intake, lower feed conversion ratio (FCR), and lower plasma triglyceride concentrations, whereas body weight gain did not differ between groups. Shotgun metagenomic analysis showed that LRFI ducks were enriched in Bacteroides-related lineages and had higher predicted capacities for complex carbohydrate degradation, lipid and energy metabolism, and cofactor synthesis, whereas HRFI ducks were enriched in taxa including Subdoligranulum variabile and Clostridioides difficile. Untargeted cecal metabolomics revealed distinct lipid- and bile acid-related metabolic profiles between the 2 groups, including differences in long-chain lipid species and bile acid-associated metabolites. Hypothalamic transcriptomic analysis identified differentially expressed genes related to neuropeptide signaling, serotonin biosynthesis, intracellular signaling, and inflammatory regulation, including NMUR2, TPH1, and PTK2B. Correlation analysis integrating microbial taxa, metabolites, and hypothalamic transcripts further revealed coordinated associations among these features in small-sized meat ducks with divergent RFI. Overall, variation in feed efficiency in ducks was associated with differences in cecal microbiota, metabolite profiles, and hypothalamic gene expression, and these results highlight candidate microbial taxa, metabolites, and genes for further validation.