Abstract

To assess the direct impact that treatment with Baytril 100 had on enrofloxacin minimum inhibitory concentrations (MICs) of potential foodborne pathogens resident in the feces of cattle, a post-approval monitoring program (PAMP) was conducted. The objective of the PAMP was to determine if administration of Baytril 100 to cattle suffering from bovine respiratory disease (BRD) was associated with changes in enrofloxacin MICs of resident E. coli and Salmonella. Forty pens of cattle from 19 different feedyards, representing 6 major beef-producing states were enrolled. Fecal samples were collected prior to treatment with Baytril 100, approximately 30 days after treatment with Baytril 100, and before the cattle were shipped to slaughter. An attempt was made to isolate generic E. coli and Salmonella from each fecal sample submitted. An MIC for enrofloxacin was determined for each isolate obtained. Approximately 27 % of the cattle became ill with BRD and were treated with Baytril 100 according to label directions. The majority of E. coli isolates (99 %) had an enrofloxacin MIC of < 0.06 µg/ml. The prevalence of E. coli isolates with MICs > 0.06 µg/ml varied from 0.3% to 1.0% to 0.1% for isolates from pre-treatment, post-treatment, and pre-slaughter samples, respectively. The use of Baytril 100 may have had a transient effect on the MICs of a few E. coli isolates (1%); however, there appears to be little correlation with changes in E. coli MICs when compared to changes seen in a potential foodborne pathogen since no effect was seen on the MICs of salmonella isolates which remained < 0.06 µg/ml.