Injectable antibiotics reprogram the gut microbiota-immune-resistome axis in ducks before detectable changes in growth performance.

Injectable antibiotics disrupt gut microbiota and immunity in ducks before detectable growth performance changes occur.

This systematic experimental study evaluated the effects of six commonly used injectable antibiotics—gentamicin sulfate, oxytetracycline, florfenicol, tylosin tartrate, lincomycin hydrochloride, and enrofloxacin—on gut microbiota composition, host immunity, tissue residues, and antimicrobial resistance gene (ARG) profiles in ducks over a 28-day trial. Despite the absence of statistically significant differences in feed conversion ratio and organ indices, antibiotic exposure produced significant subclinical disruptions. Single-molecule real-time full-length 16S rRNA sequencing demonstrated marked gut microbiota restructuring, characterized by decreased Escherichia coli abundance and enrichment of Gram-positive taxa. ELISA revealed class-dependent antibiotic accumulation in muscle tissues, with tylosin tartrate and enrofloxacin persisting through day 28, raising food safety concerns. Tissue residues were correlated with drug-specific ARG enrichment patterns and altered innate immune transcriptional profiles, including changes in inflammatory cytokines IL-6, IL-10, and TNF-α. An integrative network analysis identified TLR2, NF-κB1, TLR4, and IL-6 as central hubs linking microbiota, immunity, residues, and ARGs. These findings collectively demonstrate that injectable antibiotics initiate coordinated, measurable alterations in the host-microbiota-resistance axis before any detectable growth performance changes, underscoring the importance of subclinical monitoring. This integrative framework offers a valuable approach for assessing antibiotic-associated risks in intensive poultry production and informs more prudent antimicrobial stewardship strategies.

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