Potential for milk containing penicillin G or amoxicillin to cause residues in calves.

The potential for antibiotic residues in calves from consuming milk containing penicillin G or amoxicillin was investigated. Six calves were fed milk replacer, 6% body weight twice daily, containing 0.293, 2.92, or 5.85 microg of penicillin/ml (ppm) G or 0.25, 1.0, or 2.0 microg of amoxicillin/ml for three consecutive feedings. Urine and blood samples were collected after each feeding. Serum and urine samples were tested with a microbial receptor assay and a microbial growth inhibition assay to indicate potential drug residues. Penicillin G and amoxicillin were detected in the serum and urine of several calves 3 h after drinking spiked milk replacer. Possible violative drug residues in the calves were detected by the microbial growth inhibition assay up to 15 h after drinking spiked milk replacer. Penicillin G, but not amoxicillin, could be detected in urine 24 h after the final feeding of spiked milk replacer. Subsequently, six calves were fed milk replacer containing 11.7 microg of penicillin G/ml (ppm) twice daily, 6% body weight per feeding. Calves were slaughtered 3 h after the final feeding. Mean (+/-SD) concentrations of penicillin G measured by high-pressure liquid chromatography in liver, kidney, muscle, and serum were 0.409 (+/-0.167) microg/g, 0.031 (+/-0.012) microg/g 0.008 (+/-0.002) microg/g, and 0.013 (+/-0.006) mg/ml, respectively. This study indicates that calves fed milk with amoxicillin or penicillin G could possibly have violative residues if slaughtered within 24 h after feeding. Violative drug residues in liver tissue were found in calves slaughtered 3 h after consuming milk replacer containing 11.7 microg of penicillin G/ml (ppm).