A comparison of three bioassay techniques and high performance liquid chromatography for the detection of chlortetracycline residues in swine tissues

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Abstract
Three bioassay procedures used for the detection of chlortetracycline (CTC) residues in tissues from swine were compared with high performance liquid chromatographic analysis. Procedures were tested on incurred tissues from 3 groups of 4 pigs each treated as follows: group B, 110 mg CTC/kg diet for 28 days; group C, 220 mg CTC/kg diet for 28 days; group D, 220 mg CTC/kg diet for 21 days, followed by 7 days without CTC in the ration. A fourth group (A) of 4 pigs were fed the same basal ration as the other 3 groups without added CTC. All tissue samples from all groups tested negative by the swab test on premises (STOP) used at slaughter plants and by a laboratory microbial inhibitor test (MIT). A thin‐layer chromatography‐bioautography (TLB) procedure currently used for STOP confirmations detected CTC residues in the liver of 1 pig from group B and 2 pigs from groups C, as well as in kidneys of 3 pigs from group B. All tissues from groups B and C, with the exception of one liver from group B, contained detectable CTC residues using HPLC analysis, as did one kidney from group D. The control tissues (group A) were free of residues. The results indicated that the TLB procedure is more sensitive for the detection of CTC residues than the STOP or the MIT procedures, and that the STOP procedure is unable to detect levels of CTC in the range of 0.1 to 1.4 μ/g in livers and kidneys from swine tested at slaughter.