Potential for Milk Containing Penicillin G or Amoxicillin to Cause Residues in Calves

Abstract

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 5.85μg of penicillin/ml (ppm) G or 0.25, 1.0, or 2.0μg 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 3h after drinking spiked milk replacer. Possible violative drug residues in the calves were detected by the microbial growth inhibition assay up to 15h after drinking spiked milk replacer. Penicillin G, but not amoxicillin, could be detected in urine 24h after the final feeding of spiked milk replacer. Subsequently, six calves were fed milk replacer containing 11.7μg of penicillin G/ml (ppm) twice daily, 6% body weight per feeding. Calves were slaughtered 3h 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) μg/g, 0.031 (±0.012) μg/g 0.008 (±0.002) μg/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 24h after feeding. Violative drug residues in liver tissue were found in calves slaughtered 3h after consuming milk replacer containing 11.7μg of penicillin G/ml (ppm).