Antimicrobials administered to livestock can be excreted up to 75% in the feces and urine. Liquid swine manure from confined animal feeding operations is generally retained in lagoon storage until it is applied as a nutrient source to crop and pasture land. Thus, the applied manure becomes a possible source of antimicrobials to aquatic ecosystems. In the prairie region of Canada, lincomycin and spectinomycin are two antimicrobials that are frequently administered to pigs for prevention of post-weaning diarrhea. In order to assess the potential for contamination of prairie wetlands, concentrations of both antimicrobials were monitored in liquid manure from a commercial-scale barn during a 5-week study, and their persistence during simulated manure storage was investigated. LC-MS/MS analysis of manure extracts showed that concentrations of lincomycin and spectinomycin in the accumulating liquid manure at the end of the study were equivalent to 32 and 3%, respectively, of the doses administered to weanling pigs in their feed. In a laboratory study in which lagoon storage was simulated at room temperature using fortified liquid manure, concentrations of both antimicrobials showed a rapid initial decrease during the first 6 days, followed by a much slower dissipation, over a period of 5 months. Such persistence indicates that lincomycin and spectinomycin may be present in lagoon manure when applied as an amendment to agricultural land since many lagoons are emptied every 6 months (early spring and late fall).
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