Pork production is a significant component of the US economy. Swine manure has commonly been applied to land as a soil amendment for crop production, as it provides a valuable source of nutrients including nitrogen, phosphorus and potassium. When antibiotics are used in pork production, some fraction of the antibiotic can be excreted in manure and after land application, can be transported in runoff and enter surface water. Producers typically employ best management practices to minimize transport of these constituents after land application of swine manure. One common type of best management practice is the use of vegetated buffer strips, which have been demonstrated to reduce the transport of nutrients, bacteria and sediment in runoff from manure-amended land. To date, the ability of vegetated buffer strips to remove antimicrobials and antimicrobial resistance genes has not yet been evaluated. In this study, we investigated two objectives. Our first objective was to measure the quantities of bacitracin residues and antimicrobial-resistant pathogens/genes in swine manure and runoff from land-applied swine manure and our second objective was to quantify the removal of antimicrobials and AMR bacteria in runoff using a narrow grass hedge.

To meet these objectives, we conducted a controlled field study at the Rogers Memorial Farm at the University of Nebraska. Manure was collected from animals receiving antibiotics at the US Meat Animal Research Center in Clay Center, Nebraska, and transported to the field site, where it was applied to plots. Manure was applied to plots with and without a narrow grass hedge at a rate to meet the 3 year nitrogen requirement for corn. A series of 3 30-minute rainfall simulation experiments were conducted, and the runoff was collected from the plots. We observed that the grass hedge was consistently effective in removing tylosin from the runoff, and reduced the overall mass loading of tylosin in the runoff by 1 order of magnitude. We also evaluated removal of antimicrobial resistance genes and another gene common to bacteria, 16S rRNA. We observed mixed results for microbial gene removal in runoff, as we did not see a statistically significant removal of the resistance gene, but we did observe statistically significant removal of the other microbial gene. Taken together, our statistical analysis indicates that the grass hedges were effective at removal of microbial genes from runoff.

Our research results provide evidence that commonly used, low-cost best management practices such as narrow grass hedges can remove antimicrobials and microbial genes from runoff before it enters surface water.
For more information, please contact Dr. Shannon Bartelt-Hunt, Department of Civil Engineering, University of Nebraska-Lincoln, e-mail: [email protected], phone (402) 554-3868"".