A variety of antimicrobials are utilized in dairy cattle for both the prevention of microbial infections and growth promotion. When administered, these antimicrobials often leave the cattle unmetabolized and are found in both the urine and stool of animals. Livestock manure application is a widely used practice for fertilization of cropland and can act as the major source of antimicrobial contamination in the environment. This study seeks to investigate a variety of manure treatment practices for the presence and possible removal of common antimicrobials (including ionophores, tetracyclines, sulfonamides, macrolides, and beta-lactams). Antimicrobial levels were measured using liquid-chromatography tandem-mass spectrometry (LC-MS/MS) with sample extraction and cleanup using solid phase extraction (SPE). Ionophore residues were studied in manure along various sampling points where Livestock Water Recycling (LWR) was used. Monensin and lasalocid, two commonly used ionophores in dairy cattle, were not observed to be removed efficiently during the LWR process. Only after reverse-osmosis did the concentration of monensin reduce significantly, from 500ng/mL to below 10 ng/mL after treatment. These ionophore concentrations were also not observed to decrease upon the length of time the LWR system was installed. Tetracycline concentrations were measured in eleven farms throughout NY, MD, and PA which utilize different manure processing methods. In preliminary comparisons, tetracycline concentrations do not significantly decrease within anaerobic digestion processes. The distribution of tetracycline species (including epimers and chlorinated compounds) are not consistent among farms, suggesting various farms administer a variety of tetracycline compounds and degradation of these tetracyclines may vary depending on manure treatment. Preliminary PCR array data will be discussed and correlated to antimicrobial concentrations in order to consider risk of antibiotic presence during manure treatment to heightened abundances of antibiotic resistant genes.

Assessing dairy manure management strategies for removal of antimicrobials and spread of antimicrobial resistant genes

254th National Meeting (2017)

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