Integrated blood transcriptomic and metabolomic analyses reveal potential biomarkers associated with residual feed intake in meat ducks.

Enhancing feed efficiency is central to improving both the economic viability and environmental sustainability of poultry production. Although previous research has documented how intestinal, hepatic, and muscular nutrient metabolism contributes to feed efficiency variation, less is known about corresponding differences in circulating blood. Residual feed intake (RFI) was measured in small-sized meat ducks from 21 to 42 days of age. From a natural population of 800 ducks, the eight individuals with the highest RFI and the eight with the lowest RFI were selected to form the low RFI (LRFI, RFI = -14.95) and high RFI (HRFI, RFI = 11.72) groups, respectively. Blood samples were collected at 21 days of age for plasma biochemical analysis, metabolomic profiling, and whole-blood transcriptomic analysis. Plasma biochemical analyses showed that LRFI ducks exhibited significantly reduced triglyceride (TG) concentrations and significantly elevated glucose (GLU) and creatine kinase (CK) levels relative to HRFI birds (P < 0.05). Metabolomic profiling further revealed significant suppression of the arachidonic acid and α-linolenic acid metabolic pathways in LRFI ducks (P < 0.05). Weighted gene co-expression network analysis (WGCNA) combined with protein-protein interaction analysis identified HLX, CSF1R, MECR, RICTOR, and HTT as core genes associated with RFI, based on their network connectivity, differential expression patterns between HRFI and LRFI ducks, and evidence of selection signals (P < 0.05). Integrated metabolomic-transcriptomic analyses further highlighted key blood-based indicators linked to RFI within the arachidonic acid pathway, including metabolites (PC-O, prostaglandin G2, thromboxane B2, and 5-oxo-ETE) and genes (GGT1, HPGDS, and LCN2), which may serve as early predictive markers for selecting LRFI ducks. Collectively, these results provide a systematic characterization of blood metabolic and transcriptional differences between ducks with divergent RFI and identify potential early blood-based biomarkers that may support the genetic improvement of feed efficiency in poultry.