Efficacy of enrofloxacin in the treatment of naturally occurring acute clinical Escherichia coli mastitis

Abstract The efficacy of the combination of systemic enrofloxacin (5mg/kg twice with a 24-h interval, first dose i.v., second dose s.c.) and the nonsteroidal antiinflammatory agent ketoprofen (3mg/kg i.m. or 4mg/kg per os daily for 1 to 3 d) treatment was compared with antiinflammatory treatment only in dairy cows with naturally occurring acute clinical Escherichia coli mastitis. A total of 132 cows with acute clinical mastitis and with confirmed growth of E. coli in a pretreatment milk sample were randomly allocated to 1 of 2 treatment groups. Response to treatment was evaluated clinically and by bacteriological culturing and determination of N-acetyl-β-d-glucosaminidase (NAGase) activity on d 2 and 21 posttreatment. Enrofloxacin treatment did not increase bacteriological (90.5% of treated vs. 86.8% of nontreated cured) or clinical cure (46.7% of treated vs. 57.1% of nontreated cured), cow survival (95.3% of treated vs. 92.7% of nontreated), or quarter milk production assessed 21 d posttreatment (21.8 vs. 29.3% return to preinfection level for nontreated cows), nor did it decrease mammary gland tissue damage estimated using determination of milk NAGase activity (24.0±0.3 vs. 18.3±1.3 pmol of 4-methylumbelliferone per min per μL for nontreated cows). Treatment did not influence the number of study cows remaining in the herd after 6 mo (71.9% of treated vs. 80.6% of nontreated). The only significant effects of enrofloxacin were enhancing the bacteriological cure (odds ratio=3.32 for treated cows) and decreasing the clinical cure (odds ratio=0.05 for treated cows) on d 2 posttreatment. Our results did not support the use of enrofloxacin to treat acute clinical E. coli mastitis.