Dietary Impact on Antibiotic Resistance in Feedlot Manure

There is a growing public concern regarding antibiotic resistance and the use of antibiotics, including in livestock management. Understanding the ecology of antibiotic resistance among microbes, identifying resistance gene reservoirs, and implementing antibiotic resistance mitigation practices in livestock production are critical to protecting animal and human health while meeting increasing food demands. This research is one of several studies seeking to assess risk for livestock- to- human transfer of antibiotic resistance and to identify mechanisms for reducing that risk where possible. This study evaluated the impact of forage concentration and supplemental essential oil in beef cattle finishing diets on antibiotic resistance in freshly excreted and consolidated beef feedlot manure. Results indicate that antibiotic resistance in manure was not impacted by either of the two dietary treatments considered

Resistome and mobilome in surface runoff from manured soil as affected by setback distance

Land application of livestock manure introduces antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) into the soil environment. The objectives of this study were to examine the changes of resistome and mobilome in runoff and soil as a function of setback distance, i.e., the distance between manured soil and surface water, and to quantify the contributions of manure and background soil to the ARGs and MGEs in surface runoff. The resistome and mobilome in runoff and soil from a field-scale plot study were characterized using a high throughput quantitative polymerase chain reaction (HT-qPCR) array. It was estimated that a setback distance of ~40 m is required to reduce the total abundance of ARGs and MGEs in runoff from amended plots to that in control runoff. The resistome and mobilome of the soil in the setback region was not affected by manure-borne ARGs and MGEs. SourceTracker analyses revealed that background soil gradually became the predominant source of the ARGs and MGEs in runoff as setback distance increased. The results demonstrate how manure-borne ARGs and MGEs dissipated in agricultural runoff with increasing setback distance and had limited impacts on the resistome and mobilome of soil within the setback region

Mitigation Strategies for Antimicrobial Resistance and Nutrients at Critical Control Points in Livestock Manure Management Systems

Livestock waste is regarded as an important source of antimicrobial resistance (AMR) and nutrients in the environment. This study focuses on developing novel manure management practices to mitigate the dissemination of AMR and nutrients at critical control points within the manure management system. The interventions tested include 1) lime amendment of pen floor surface materials in open feedlots for the reduction of AMR bacteria and genes, 2) heat treatment by conductive concrete slabs for the transformation of phosphorus P and nitrogen N in beef cattle manure stockpiles, and 3) setback distance, the distance between manured soil and surface water, as a means to reduce AMR genes in surface runoff following the land application of swine manure slurry. First, the application of lime to pen floor surface materials in open cattle feedlots significantly reduced the concentrations of AMR bacteria and genes. Stockpiles of lime-amended manure showed a significantly lower AMR bacteria and gene levels compared to stockpiled manure from control pens that received no lime. Beta diversity analysis showed that lime altered the microbial compositions in both pen floor surface materials and stockpiled manure. Second, bench-scale tests showed that the heat from a conductive concrete slab increased the fraction of the readily available NaHCO3-P in stockpiled manure. The concentrations of ammonium-N, total N, and total P were greater in runoff generated from the heat-treated manure after 10 days of stockpiling. Third, a high throughput quantitative polymerase chain reaction array was used to assess the resistome and mobilome in runoff and soil from field plots. The abundance of AMR genes and mobile genetic elements (MGEs) in runoff from manured plots decreased with increasing setback distance. A setback distance of ~40 m was estimated to reduce the total abundance of AMR genes and MGEs in runoff from manured plots to that of control runoff. SourceTracker analysis revealed that background soil gradually became the predominant source of AMR genes and MGEs in runoff as setback distance increased. These findings highlight potential mitigation strategies that stakeholders and farmers can use as best management practices to reduce AMR dissemination and nutrient loss from livestock manure

Influence of Setback Distance on Antibiotics and Antibiotic Resistance Genes in Runoff and Soil Following the Land Application of Swine Manure Slurry

The environmental spread of antibiotics and antibiotic resistance genes (ARGs) from the land application of livestock wastes can be a potential public health threat. The objective of this study was to assess the effects of setback distance, which determines how close manure may be applied in relation to surface water, on the transport of antibiotics and ARGs in runoff and soil following land application of swine manure slurry. Rainfall simulation tests were conducted on field plots covered with wheat residues, each of which contained an upslope manure region where slurry was applied and an adjacent downslope setback region that did not receive slurry. Results show that all three antibiotics (chlortetracycline, lincomycin, and tiamulin) and seven out of the ten genes tested (erm(B), erm(C), intI1, tet(O), tet(Q), tet(X), and the 16S rRNA gene) decreased significantly in runoff with increased setback distance. Only blaTEM, chlortetracycline, and tiamulin decreased significantly in surface soil with increased setback distance, while the other analytes did not exhibit statistically significant trends. By using linear regression models with field data, we estimate that a setback distance between 34−67 m may allow manure-borne antibiotics and ARGs in runoff to reach background levels under the experimental conditions tested. Includes Supplemental file

Influence of Setback Distance on Antibiotics and Antibiotic Resistance Genes in Runoff and Soil Following the Land Application of Swine Manure Slurry

The environmental spread of antibiotics and antibiotic resistance genes (ARGs) from the land application of livestock wastes can be a potential public health threat. The objective of this study was to assess the effects of setback distance, which determines how close manure may be applied in relation to surface water, on the transport of antibiotics and ARGs in runoff and soil following land application of swine manure slurry. Rainfall simulation tests were conducted on field plots covered with wheat residues, each of which contained an upslope manure region where slurry was applied and an adjacent downslope setback region that did not receive slurry. Results show that all three antibiotics (chlortetracycline, lincomycin, and tiamulin) and seven out of the ten genes tested (erm(B), erm(C), intI1, tet(O), tet(Q), tet(X), and the 16S rRNA gene) decreased significantly in runoff with increased setback distance. Only blaTEM, chlortetracycline, and tiamulin decreased significantly in surface soil with increased setback distance, while the other analytes did not exhibit statistically significant trends. By using linear regression models with field data, we estimate that a setback distance between 34−67 m may allow manure-borne antibiotics and ARGs in runoff to reach background levels under the experimental conditions tested. Includes Supplemental file