Detecting Oxytetracycline Residues in Chicken Tissues Using the Delvotest^® P System

Oxytetracycline spiked chicken liver and kidney were tested for residues using Delvotest P and the results compared to standard plate assay using Bacillus cereus as test organism. Delvotest P detected all replicates at concentrations of ≥0.62 μg/g in liver and kidney. Between 0.41-0.2 μg/g, the responses were mixed (positive, doubtful, and negative); at 0.1 ≥ concentration, the responses were negative. The limit of detection of the plate assay was 0.2 and 0.31 μg/g for liver and kidney, respectively. Residue analysis on tissues from chickens dosed twice daily (for 4 d) with 25 mg/kg oxytetracycline was carried out using the Delvotest P and the plate assay. Delvotest P responses were all positive for 1-4 h after treatment in kidney and 1 and 2 h in liver and serum. Muscle never achieved concentrations that were consistently positive. The plate assay detected drug from 0.5-6 h in serum, from 0.5-8 h in liver and kidney, and at 4-6 h in muscle. Kidney tissue appeared to be the best for detecting oxytetracycline residues in chicken. The Delvotest P method was simpler to use and required less time; 3-4 h compared to about 18 h for the plate assay.