Purpose: To evaluate an immunochromatographic assay and kidney inhibition swab (KIS) test for the determination of penicillin G residues in sow urine.
Methods: Sows (n=126; 228±30.1 kg) were administered daily IM doses of penicillin G procaine (33,000 U/kg bw; 5x the label dose) for 3 consecutive days using 3 different administration patterns. Urine was screened for penicillin G using the KIS test as well as by an immunochromatographic assay. The urine samples were diluted with milk prior to processing for the immunochromatographic procedures. For the KIS test the presence of penicillin G was indicated by the development of a purple color.
Results: Using a simple modification consisting of the addition of whole milk, we were able to adapt a commercially available immunochromatographic assay designed for use in milk for use in identifying penicillin G in sow urine. Immunochromatographic assay results were comparable with the KIS test results with 96% accuracy. When KIS test accuracy was compared between assays performed in 2012 and 2015 there was 98% agreement, indicating stability of penicillin G in urine under storage conditions of -80°C. LC-MS/MS results confirmed penicillin G concentrations did not differ between measurement years.
Significance: Both KIS test and immunochromatographic assay methods can be performed “onsite” and produced similar results, but immunochromatographic assays provided “real time” (5 min testing time) answers in comparison to KIS test which require ~4 hours. Nevertheless, either rapid screening method could be used onsite to determine penicillin G residues in sow urine prior to marketing.