INFLUENCE OF SWINE MANURE STORAGE AND LAND APPLICATION PRACTICES ON MITIGATING THE SPREAD OF ANTIBIOTIC RESISTANCE IN THE ENVIRONMENT

The environmental spread of antibiotics and antibiotic resistance genes (ARGs) from livestock production can be a potential public health threat if these contaminants reach surface water or groundwater. The storage and land application processes for swine manure slurry are critical in mitigating the spread of these two classes of contaminants in the environment. In this thesis, two projects related to the mitigation of antibiotics and ARGs are reported. The first project investigated the impact of varying setback distances on the concentrations of antibiotics and ARGs in runoff and soil. The experiment was conducted on a series of plots in the summer of 2016 at a farm located outside Lincoln, NE. Each plot had a manured region followed by a downslope setback region. A portable rainfall simulator was used to simulate rainfall. Runoff and soil samples were collected at various setback distances downslope of the manured region. Results show that seven out of the ten genes and all three antibiotics identified in manure decreased significantly with increased setback distance in both runoff and soil. Both ARG and antibiotic concentrations decreased with increasing soil depth. The STWIR/KINEROS2 model was successfully adopted to describe the ARG concentrations in runoff using field data The second project studied the impacts of six pit additives and four disinfectants on the concentration of ARGs in swine manure during simulated storage. The experiment was conducted in 2018 and involved 57-L reactors containing manure. Pit additives or disinfectants were added to individual reactors, two reactors per pit additive or disinfectant, and the reactors were monitored and sampled over 40 days. Results showed that one pit additive and one disinfectant were effective in reducing most of the ARGs tested in manure during simulated storage. Results from these two projects can aid in evaluating or developing best management practices (BMPs) to be used in swine manure management. Advisors: Xu Li and Shannon Bartelt-Hun