Rearing systems shape the successional dynamics of the gut microbiota, resistome, and mobilome in Lueyang Black-boned chickens

Understanding the ecological factors shaping antimicrobial resistance (AMR) dissemination in agricultural environments is critical for global "One Health". Here, we performed metagenomic sequencing to investigate the impact of intensive cage-reared (CR) and free-range (FR) systems on the gut microbiota, resistome, and mobilome dynamics of Lueyang Black-boned chickens across different production stages. Our analyses revealed that distinct rearing systems drove resistome alterations by reshaping microbial community assembly and horizontal gene transfer (HGT) pathways. Specifically, the CR system imposed strong deterministic stress, thereby enriching opportunistic taxa (such as Desulfovibrio) and promoting a highly connected but topologically fragile microbial network. Conversely, the FR system exhibited a higher total abundance of commensal resistance genes, a process mainly driven by diverse transposon-mediated integrations including tnpA and ISBf10. In contrast, the CR system was associated with high-risk, clinically relevant resistance determinants. These included extended-spectrum beta-lactamases and multidrug resistance cassettes. Targeted network tracking unmasked highly divergent potential host-vector-ARG associations. Resistance expansion under confined CR conditions showed strong vector-dependency, being fundamentally linked to the broad-host-range plasmid IncQ1 alongside clinically relevant mobilization elements, including Class 1 integrons. Longitudinally, the FR resistome achieved ecological stabilization. In contrast, the CR microbiota exhibited continued genetic flux, continuously acquiring transient resistance elements during the observed production period. These findings demonstrate that welfare-friendly rearing management serves as a critical ecological intervention to limit the proliferation of mobile, high-risk resistance traits. Ultimately, future agricultural surveillance must transition beyond quantifying total resistance gene abundance to prioritize functional risk assessments and mobilization potential.