Depletion of Intramuscularly Injected Ceftiofur from the Milk of Dairy Cattle

Abstract

Ceftiofur sodium, a new broad-spectrum cephalosporin, has been approved in the US, Canada, and several other countries throughout the world to treat bovine respiratory disease in cattle and dairy cows. In Experiment 1, 6 lactating cows were intramuscularly treated with 2.29mg of [14C]ceftiofur/kg of BW daily for 5 d. In Experiment 2, 30 additional cows at three locations were similarly treated with 2.2mg of ceftiofur (unlabeled)/kg of BW. Milk was collected every 12 and 24h after each dose and every 12h up to 5 d after the last dose. The majority of milk samples, both during treatment (12 and 24h after each dose) and after the last dose (up to 5 d following ceftiofur treatment), were negative by screening procedures based on microbial inhibition (Delvotest-P®, Bacillus stearothermophilus disk assay, and cylinder plate assays). The receptor-binding Charm Test II assay, which has a limit of detection of .005ppm of ceftiofur, gave positive tests for milk samples up to 48h following treatment. When the Charm Test II assay is used with .008 IU/ml of penicillin as a positive control, 44% of the samples from individual cows were negative at 12h posttreatment. Ninety percent of the samples from individual cows were negative at 24h after the last treatment.The use of ceftiofur in dairy cattle in accordance with the label directions does not result in total residues in milk higher than the FDA-calculated safe concentration of 1-ppm ceftiofur equivalents. The milk from individual cows did not test positive by the commercial screening assays examined in this study, except for the Charm Test II. The Charm Test II was 90% negative using the Charm Sciences criteria at 24h after the last treatment.