Longitudinal source-sink dynamics of fecal litter and farm indoor environmental resistomes in broiler chicken and Cherry Valley ducks

Antimicrobial resistance is a major One Health threat, and intensive poultry systems function as amplifiers. Although broilers and ducks are reared under similarly controlled conditions, their microecologies diverge. Integrated, longitudinal source-sink analyses quantifying overlap and directional flux between host-associated and environmental resistomes remain scarce. A two-year (2022–2024), longitudinal, commercial-scale comparison was undertaken across 15 stocking cycles under harmonized husbandry in Ross 308 broiler and Cherry Valley duck. Parallel shotgun metagenomics profiled fecal litter and farm indoor environments across standardized production, with daily monitoring in one complete cycle per system; in total, 96 pooled samples were sequenced to quantify cross-compartment overlaps. Antibiotic resistance gene (ARG) reservoir dominance proved to be system-specific, duck systems were environment-centric, whereas broiler systems were fecal litter-centric. Although overall ARG diversity was similar between systems (broiler 2,542; duck 2,494 types), ducks exhibited greater compartmental divergence, with ~ 2.6-fold more environment-unique ARGs than paired fecal litter and 1.15-fold higher environmental richness than broilers. Compartment coupling also differed: broilers showed tighter host-environment overlap, while ducks were more partitioned. A shared environmental ARG pool (57.5%) indicated substantial cross-system exchange potential. Temporally, shared ARGs accumulated across the grow-out and peaked pre-depopulation. The distribution of significant ARG carrier species revealed asymmetric host-environment coupling: overlap across compartments was 66.67% in broilers versus 45.45% in ducks, notably. The impact of antimicrobial use was nuanced: short, targeted courses were associated with lower aaAMR burden overall Collectively, the recurrent detection of clinically consequential carriers (P. aeruginosa, E. coli, A. baumannii, S. aureus, K. pneumoniae, S. maltophilia, toxigenic Clostridium spp.) underscored One Health risks of zoonotic spillover and food-chain contamination. Reservoir behavior in intensive poultry systems should be treated as system-specific, and matrix-targeted, with biofilm and humidity management prioritized in duck operations, and litter/manure control emphasized in broilers. The finisher-depopulation window emerges as a critical intervention point, warranting intensified mitigation clean-out. Finally, mitigation should extend beyond individual farms to transport crates, vehicles, shared equipment, and supply chains.