Milk and Tissue Residue Depletion of Two Intramammary Dry Cow Antimicrobials in Dairy Goats

The goal of this project was to provide residue depletion data for two common dry cow antimicrobial treatments - cloxacillin benzathine (CLOX) and cephapirin benzathine (CEPH) to assist in establishing meat and milk withdrawal intervals. In each portion of this study, does were treated with a full tube of their assigned treatment in each half of the udder. Samples were analyzed using liquid chromatography with tandem mass spectroscopy. Twenty-six animals were treated with CLOX at dry-off and sacrificed at 3, 7, 21, 28, 35, 42, and 49 days posttreatment. Cloxacillin was present in kidney and liver through 35 days posttreatment but was not found in muscle at any time point. The highest concentration of CLOX was 0.438 μg/g in liver and 0.342 μg/g in kidney, both at three days posttreatment. Thirty-two does received CEPH at dry-off, and animals were sacrificed at 1, 2, 4, 6, 21, 28, 35, 42, and 49 days posttreatment. Cephapirin was not detected in any tissue at any timepoint. To complete the milk residue depletion study, 22 does were randomly assigned to CLOX treatment at dry-off and 22 additional does were treated with CEPH. One CLOX doe was unenrolled from the study at 144 h postkidding for prolonged residue production with a final reading of 57.3 ng/g. Only three CEPH-treated does shed detectable residues after kidding, and no residues were detected after 60 h postkidding. The highest concentration of CLOX was 413.0 ng/g at the first milking while the highest concentration of CEPH was 14.0 ng/g at the first milking.