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A pair-matched longitudinal study conducted on three dairy farms in the U.S. High-Plains explored the temporal effects of two-dose ceftiofur crystalline-free acid (CCFA) treatment for metritis on third-generation cephalosporin (3GC) resistance among enteric E. coli in Holstein-Friesian cows. The current 13-day slaughter withholding period does not account for rising populations of third-generation cephalosporin (3GC) resistant bacteria in feces of animals following CCFA treatment. A total of 124 matched-pairs of cows were enrolled in the study. Cows diagnosed with postpartum metritis received the product twice at the labeled dose of 6.6 mg/kg subcutaneously at the base of alternating ears. Untreated cows–absent clinical metritis–were matched on lactation number and calving date. Feces were collected per rectum on days 0 (baseline), 6, 16, 28, and 56. Environmental samples, from watering troughs as well as surface manure from fresh-cow, hospital, maternity, and milking pens, and from the compost pile were collected prior to the animal sample collection period. Historical data on metritis rates and CCFA use were compiled from herd records. On day 0, cows exhibited an overall mean difference of over 4 log10 colony forming units (CFU) comparing 3GC resistant E. coli to the general E. coli population. At the first eligible slaughter date, the difference declined to 3.31 log10 CFU among cows in the CCFA group (P<0.01 compared to control cows). Such differences were no longer observed between the treated and control groups by day 28. Results suggest a 13-day withholding period following the final treatment is insufficient to allow levels of 3GC resistant E. coli to return to baseline. This effect varied by farm and was dependent upon the starting level of resistance. A farm-specific extended slaughter-withholding period could reduce the microbial risk to food products at slaughter. [ABSTRACT FROM AUTHOR]

Objective-To determine the effect of intrauterine administration of ceftiofur sodium on fertility and the risk of culling in postparturient cows with retained fetal membranes (RFM), twins, or both. Design-Single-blind randomized clinical trial and prospective cohort study. Animals-2,442 cows that calved from January 1, 2000, to May 31, 2001. Procedure-Cows with RFM, twins, or both were randomly allocated to control or treatment (ceftiofur) groups. Ceftiofur-group cows received 1 g of ceftiofur sodium sterile powder reconstituted with 20 mL of sterile water as a single intrauterine infusion once between 14 and 20 days after parturition. Control-group cows received no treatment. Cows that calved but did not have RFM or twins were considered the referent group. Reproductive, culling, and health data were recorded. Results-There was no significant difference in the overall proportion of ceftiofur-group cows confirmed pregnant, compared with cows in the control group. Ceftiofur-group cows were significantly less likely to be culled and were culled at a later time in lactation than control-group cows. In the cohort study, the risk of pregnancy and the risk of being culled in ceftiofur-group cows were not significantly different from cows in the referent group. Conclusions and Clinical Relevance-intrauterine treatment of cows with RFM, twins, or both with ceftiofur sodium increased longevity of cows in the herd as measured by the risk of culling and the time to culling. Intrauterine administration of ceftiofur in cattle is considered extralabel drug use, and the attending veterinarian must follow the AMDUCA guidelines for extralabel drug use. [ABSTRACT FROM AUTHOR]