Conventional vs antibiotic-free farming and antimicrobial resistance in food: a meta-analysis

Background

Conventional farming may increase antimicrobial resistance (AMR) in food before processing, yet the magnitude of this association remains poorly characterised. This systematic review and meta-analysis compared phenotypic AMR in unprocessed food matrices between conventional production systems and antibiotic-free, organic, or wildlife comparators.

Methods

Databases were searched from inception to Feb 28, 2025 (protocol: osf.io/pf7b4). Quality was assessed using validated tools. For each antibiotic, summary odds ratios (ORs) with 95% confidence intervals (CIs) were estimated using restricted maximum-likelihood random-effects models, with prespecified subgroup analyses by matrix and bacterial genus.

Findings

Eleven studies, mostly cross-sectional and of moderate-to-high quality, met inclusion criteria, covering dairy cattle (n = 6;raw milk), swine (n = 2;carcasses), and poultry (n = 3;eggs and carcasses). Conventional farming was associated with significantly higher ORs to ampicillin (OR 2·89, 95% CI 1·64–5·09; I²=34%), penicillin (OR 1·57, 95% CI 1·12–2·19; I²=7%), tetracycline (OR 3·37, 95% CI 1·83–6·18; I²=52%), erythromycin (OR 3·00, 95% CI 1·36–6·62; I²=72%), spiramycin (OR 5·24, 95% CI 1·04–26·41; I²=0%), tylosin (OR 4·54, 95% CI 1·02–20·11; I²=0%), and pirlimycin (OR 4·42, 95% CI 1·42–13·83; I²=33%). Teicoplanin showed a significant association (OR 4·04, 95% CI 1·10–14·88), and rifampicin a significant inverse association (OR 0·15, 95% CI 0·03–0·70). Subgroup analyses showed the strongest associations in raw milk and for Staphylococcus spp.

Interpretation

Conventional production was associated with higher phenotypic AMR in pre-processing food, indicating a measurable resistance footprint entering the human supply chain. These findings support WHO stewardship priorities targeting agricultural use of critically important antimicrobials and highlight the need for production-level surveillance to safeguard food system sustainability and planetary health.

Key messages

• Conventional farming is associated with higher antimicrobial resistance in unprocessed food matrices compared to antibiotic-free, organic, or wildlife comparators, across dairy, swine, and poultry.

• A measurable resistance footprint enters the food supply chain at production level, supporting WHO priorities on agricultural antimicrobial stewardship and the need for production-level surveillance.