Antibiotics and antibiotic resistant bacteria and genes in northeastern dairy manure management systems - Project overview and preliminary findings from an 11 farm case study

Modern U.S. dairies use antibiotics primarily for disease treatment and prevention. Consequently, antibiotic residues, antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG) present in dairy manure may potentially enter the environment and contribute to the spread of antibiotic resistance (AR). Working cooperatively with 11 production dairies in three states (NY, PA, MD) our objective is to investigate the efficacy of existing on-farm manure management practices (e.g. long-term storage, composting, anaerobic digestion, etc.) at mitigating these potential contaminants. At each farm manure system performance is being assesses, antibiotic usage is being tracked, and manure samples are being collected at roughly 6-week intervals over 2-years pre- and post-each treatment step of the various manure handling systems. Samples are being analyzed for tetracycline, sulfonamide and macrolide antibiotic residues. Additionally, using culturing techniques and qPCR, ARB in manure solids before and after treatment are being quantified to study the effectiveness of bedding recovery systems at mitigating ARB pathogens. Select samples are also being analyzed for their diversity and abundance of ARGs. Preliminary data shows variable mitigation potentials of the different manure handling systems and is improving our understanding of the fate of these potential contaminants in dairy manures. As the project advances the efficacy of specific treatment systems to mitigate AR will be tested and knowledge on the fate of AR in dairy manure management systems will be extended to the dairy industry.