#10-119

Complete

Date Full Report Received

10/24/2011

Date Abstract Report Received

10/24/2011

Investigation

Institution:
Primary Investigator:

The use of antibiotics by the swine industry to increase production efficiency and treat disease is thought to contribute to antibiotic resistance in the environment.  When manure from hog operations is applied to fields with subsurface drainage, it is possible that the antibiotics and bacteria with resistance will be transported through tile systems and discharged into surface waters.  To investigate this, tylosin, enterococci (a pathogen indicator organism), and antibiotic resistance genes (ARGs) were assessed in manure, soil and tile water samples.  Manure from a swine facility which administers tylosin at sub-therapeutic levels was applied to chisel plow and no-till plots with separate tile drains.  Of the four test plots, two had manure applied and two received standard nitrogen UAN applications, serving as controls. Manure samples were collected in the fall of 2010 at the time of application.  Soil samples were collected both in the manure injection bands and from soil between the bands right after manure application and again the following spring.  Water samples were collected from tile lines on a weekly basis from late spring until the water ceased to flow in mid-summer.  Based on the results of this study, a few encouraging conclusions can be made for pork producers regarding the presence of ARGs, tylosin, and tylosin-resistant enterococci in manure, soil and tile water.  Tylosin-resistance genes were detected in elevated concentrations in soil in the manure injection zone, compared to soil outside the manure band or in soil not treated with manure. However, the transport of tylosin resistance genes in drainage water were at concentrations much less than in the manured soil and drainage water from manured soils and non-manured soils were similar in their concentrations of tylosin-resistance genes.  Concentrations of enterococci in tile water are very low, and only exceeded the geometric mean for recreational waters 9 times, with 33% of these exceedences occurring in tile flow from the control plots.   Tylosin concentrations in tile water were also very low, all less than 1 part per billion, and 95% lower than concentrations detected in swine manure samples applied to the plots. While the concentration of ARGs is much higher in water relative to the concentrations of detected resistant enterococci, it is unknown in which organisms these genes reside.  Based on the results of our work, there appears to be differences in bacterial and antibiotic transport between tillage practices, and this is likely a function of the plot hydrology.  Since 2011 was a very dry year, continued monitoring is recommended for better assessment of land management practices on contaminant transport.

For questions, contact:
Michelle Soupir
Assistant Professor, Agricultural and Biosystems Engineering
Iowa State University
3163 NSRIC
Ames, IA 50011-3310
515-294-2307