Efficacy of enrofloxacin for the treatment of acute clinical mastitis caused by Escherichia coli in dairy cows

Evidence for the efficacy of antimicrobial treatments in Escherichia coli mastitis is limited. The aim of this double-blinded field trial was to investigate the efficacy of enrofloxacin compared with placebo, with a special focus on survival, in dairy cows with acute clinical mastitis caused by E. coli. Dairy cows (n=116) with acute clinical mastitis were included in the study. A clinical examination was performed and a milk sample from the affected udder quarter was collected for investigation of somatic cell count (SCC) and bacteriology on the first day of treatment (day 0) and at day 3 (clinical examination only), day 22 and day 28. Data regarding culled cows, SCC and daily milk yield were retrieved from monthly milk recording each month until 180 days after treatment. All cows were treated with either enrofloxacin or placebo once a day for three days, starting at day 0. After culturing, 56 cows with confirmed E. coli mastitis remained in the study. Nine (16 per cent) of them died within the first week. Enrofloxacin-treated cows had lower SCC compared with placebo-treated cows at first monthly milk recordings after being treated for mastitis. Treatment with enrofloxacin did not result in a higher probability of survival compared with placebo.