Penicillin Residue in Milk Following Administration of Increasing Doses of Procaine Penicillin G

Abstract

The objective of this study was to determine the highest dose of procaine penicillin G (PPG) which could be administered to allow a withdrawal period of 96 hours in the milk in milking dairy cows. Using two 4x4 latin square designs, two groups of lactating dairy cows (n=4 per group) received 4 different doses (7,000, 14,000, 21,000 and 28,000 IU/kg 20 mL/site of a 300 000 IU/mL of PPG . Each dose was administered once daily for 5 consecutive days to each cow by either the intramuscular (square 1) or subcutaneous route (square 2). Each cow received a new dose every 3 weeks. Milk samples were collected before administration and at 12, 24, 36, 48, 60, 72, 84, 96, 108, 120 and 132 hours following the last day of administration. Concentration of penicillin in milk was measured using a quantitative Bacillus stearothermophilus disc method.

For all 4 doses administered via the intramuscular route all the animals (n=4) had milk penicillin concentration less than 0.016 IU/mL by 84 hours. However, the cows that received the PPG via the subcutaneous route had penicillin concentration less than 0.016 IU/mL by 84 hours for the dosage of 7,000, 14,000 and 21,000 IU/kg while the penicillin concentrations remained higher than 0.016 IU/mL for 108 hours after the administration of the 28,000 IU/kg dose. Residual milk concentrations of penicillin were more variable and less predictable than those from the intramuscularly-injected cows. The results of this study indicate that the dose of 21,000 IU/kg is safe with 96 hours withdrawal in milk whichever route of administration.