Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/7/2017
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: Introduction It is not known how removal of cattle from a backgrounding operation will affect the persistence of antibiotic resistance genes (ARGs) in the environment. Our objective was to investigate the effect of destocking on the persistence and distribution of ARGs in the backgrounding environment. Methods The study was conducted at pasture-feedlot type cattle backgrounding operation which consisted of an outdoor feeding and grazing areas separated by a fence with an access gate. Two batches of weaned calves (n=120) spent a 4-month growing period at the backgrounding facility in 2010. Soil samples (n=78) from 13 georeferenced sites were collected before animals were removed (2010) then one year (2011) and two years (2012) after cattle were removed. Total soil community DNA was extracted and total bacterial population (16s rRNA), enterococci and integrase gene of class 1 integrons (intI1), and tetracycline (tetO, tetW and tetQ), erythromycin (ermB and ermF) and sulfonamide (sul1 and sul2) resistance genes were quantified. Spatial and statistical methods were used to analyze the data. Results The concentrations of total bacteria, enterococci, intI1, and ARGs showed spatial variation between the feeding and grazing areas. They were higher in the feeding area and in its immediate vicinity (around the fence and the gate) which was then followed by a gradient decline along the grazing area. Regardless of the sampling year the concentrations of total bacteria, enterococci and intI1and ARGs were higher in the feeding area compared to the grazing area. In the grazing area, the concentrations of total bacteria, enterococci, intI1 and ARGs remained unchanged over the two years period after cattle were removed compared to the 2010 level when cattle were present on the facility. In the feeding area, the concentrations of total bacteria remained unchanged over the two years period compared to the 2010 level. On the other hand, the concentrations of enterococci, intI1 and ARGs showed significant but small reduction (one to two log10 reduction) two years after cattle were removed. Conclusions Higher concentrations of ARGs were observed in the feeding area compared to the grazing area of the backgrounding facility. Destocking for two years did not produce a biologically meaningful reduction in the concentration of ARGs.