Global trends in antimicrobial resistance on organic and conventional farms

Abstract

Various stewardship policies, regulations, and voluntary bans have focused on protecting antimicrobials by limiting their use in livestock. These efforts ignited management shifts ranging from largely nominal (e.g., drugs banned for use as growth promoters were reclassified as prophylactic drugs) to organic farming, which drastically reduces or eliminates use of antimicrobials. Understanding how these farming practices influence the prevalence of antimicrobial resistance in livestock carries important implications for policy makers, public health officials, and farm managers. Here, we reviewed studies spanning the last 20 years to ask if the most stringent effort to reduce antimicrobial use in livestock -- organic farming -- results in notable reductions in the prevalence of antimicrobial resistance across broad scale geographic ranges, pathogens, and livestock hosts. Our results validate organic farming in reducing the prevalence of antimicrobial resistance (AMR) by [~]31.2%,[~]26.9%, [~]28.2%,[~]42.9 and [~]36.2% in cattle, chicken, environment, pigs and turkey respectively while also revealing significant variation in the strength of this reduction across contexts. Given that our results join others indicating that AMR is increasing across all types of farms, our results highlight areas where organic farming has been most effective and may provide economical and scalable solutions for farmers.