Three calves were each injected with a single intramuscular (IM) dose of penicillin G procaine at either 3750, 7500, or 15000 IU per kg of body weight and killed at 24 h postinjection, along with a control calf that had not received penicillin. Tissues were tested by the Swab Test on Premises (STOP), the Calf Antibiotic and Sulfa Test (CAST), the Brilliant Black Reduction Test (BBRT), the Charm Test II, thin layer chromatography - bioautography (TLC/BA), and high performance liquid chromatography (HPLC). Samples of muscle, liver, and kidney from all injected calves contained detectable penicillin residues when analyzed by HPLC. The BBRT and Charm Test II were the most sensitive test kits for penicillin G in muscle, while the Charm Test II also detected residues in livers and kidneys from all injected animals. The STOP and CAST were less sensitive, although improved performance was observed for the STOP using a modified growth medium. Penicillin residues were detected in all livers and kidneys from injected animals using TLC/BA. Urine collected from injected animals 12 and 24 h postinjection was positive by the Live Animal Swab Test (LAST). All urine and tissue samples from the control animal were negative. The BBRT and Charm Test II appear to offer greater sensitivity for penicillin G residues than such currently used procedures as STOP and CAST but should be confirmed by a suitable laboratory method, such as the HPLC procedure used in this study.

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