Manure management reduces levels of antibiotics and antibiotic resist...( MADISON WI November 26 2007- Antibio...)

MADISON, WI, November 26, 2007- Antibiotic resistance is a growing human health concern. Researchers around the globe have found antibiotics and other pharmaceuticals to be present in surface waters and sediments, municipal wastewater, animal manure lagoons, and underlying groundwater. In a recent article in the November-December issue of Journal of Environmental Quality, researchers at Colorado State University (CSU) describe a study to find out if animal waste contributes to the spread of antibiotics and antibiotic resistance genes (ARG), and if they can be reduced by appropriate manure management practices.

In the study, funded by the USDA Agricultural Experiment Station at CSU and the National Science Foundation (NSF), researchers investigated the effects of manure management on the levels of antibiotics and ARG in manures. The study was conducted at two scales. In the pilot-scale experiment, horse manure was spiked with the antibiotics chlortetracycline, tylosin, and monensin and compared to horse manure that was not spiked with antibiotics to determine the response of ARG in unacclimated manures. In the large-scale experiment, dairy manure and beef feedlot manure, which were already acclimated to antibiotics, were monitored over time.

The manures were subjected to high-intensity management (HIM-amending with leaves and alfalfa, watering, and turning) and low-intensity management (LIM-no amending, watering, and turning) for six months. During this time, the levels of antibiotics were monitored using high-performance liquid chromatography (HPLC) and tandem mass spectrometry (MS/MS). In addition, two types of ARG that confer resistance to tetracycline, tet(W) and tet(O), were monitored using quantitative polymerase chain reaction (Q-PCR).

In the pilot study, chlortetracycline, tylosin, and monensin all dissipated more rapidly in the HIM-manure than in the LIM-manure. In the large-scale study, feedlot manure initially had higher co
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