Successful treatment of recurrent subclinical mastitis in cows caused by enrofloxacin resistant bacteria by means of the sequential intramammary infusion of enrofloxacin HCl-2H 2 O and ceftiofur HCl: a clinical trial

ABSTRACT

Background@#Recurrent subclinical mastitis (RScM) due to resistant bacteria has low clinical and bacteriological cure rates, often requiring the culling of cows. The sequential intramammary administration of enrofloxacin hydrochloride-dihydrate (enro-C) followed by ceftiofur HCl may be useful for treating these cases. @*Objectives@#This study assessed the bacteriological and clinical cure-efficacies of the sequentially intramammary administration of enro-C, followed by ceftiofur HCl to treat RScM in Holstein/Friesian cows. @*Methods@#This trial was conducted in a herd with a high prevalence of RScM, and 20 Holstein/Friesian cows were included 45% suffering subclinical mastitis and 38.9% of the mammary quarters affected. Twenty-nine bacterial isolates in vitro resistant to enro-C were obtained (coagulase-negative Staphylococcus spp, 55.2%; Staphylococcus aureus, 27.6%;Escherichia coli, 6.9%; Streptococcus uberis, 6.9%; Corynebacterium bovis, 3.4%). Polymerase chain reaction-isolated the following genes linked to enro-C resistance chromosomal (gyrA) and plasmid (aac(6')-lb-cr). The treatments were as follows twice-daily intramammary infusions of enro-C (300 mg/10 mL) for 5 days. Cows clinically considered treatment failures were also treated with intramammary ceftiofur (125 mg/10 mL, twice daily for 5 days. The clinical and bacteriological cure rates were carried out when completing each treatment phase and at 14 and 21 days, aided by a California mastitis test, somatic cell count, and failure to identify the initially causative bacteria. @*Results@#Enro-C achieved 65% clinical and bacteriological cure rates, and 100% cure rates were obtained after the rescue treatment with ceftiofur HCl. @*Conclusions@#Outstanding clinical and bacteriological cure rates in cows affected by RScM were achieved with the consecutive intramammary infusions of enro-C, followed by ceftiofur HCl.