<i>Antibiotics and antibiotic resistant bacteria and genes in northeastern dairy manure management systems � Project overview and preliminary findings from an 11 farm case study</i>

Abstract

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.

Invited review: Fate of antibiotic residues, antibiotic-resistant bacteria, and antibiotic resistance genes in US dairy manure management systems

“…Unlike tetracyclines, the widely used β-lactam antibiotics are more soluble and seemingly less persistent (Table 2). In our study of over 80 fresh manure samples collected from 11 northeastern US dairy operations over a 15-mo period, no β-lactam residues were detected in any manure samples, despite the common use of penicillins and cephalosporins on these dairy operations (Oliver et al, 2017). To our knowledge, the only study of dairy cows to measure a β-lactam residue found very low levels of cephapirin and only in pre-excreted cecal samples and cow urine collected with a catheter (Ray et al, 2014).…”