Efficacy of extended pirlimycin therapy for treatment of experimentally induced Streptococcus uberis intramammary infections in lactating dairy cattle.

ABSTRACT Streptococcus uberis is an important cause ofmastitis in dairycowsthroughout the world,particularly during the dry period, around thetime of calving, and during early lactation.Strategies for controlling S. uberis mastitis hav enot received adequate research attention andare therefore poorly defined and inadequate.Objectives of the present study were to evalu-ate the efficacy of extended therapy regimenswith pirlimycin for treatment of experimental-ly induced S. uberis intramammary infectionsin lactating dairycows during early lactationand to evaluate the usefulness of the S. uberis experimental infection model for evaluatingantimicrobial efficacy in dairycows. The effi-cacy of extended pirlimycin intramammarytherapy regimens was investigated in 103mammary glands of 68 dairy cows that becameinfected following experimental challenge with S. uberis during early lactation. Cows infectedwith S. uberis in one or both experimentallychallenged mammaryglands were randomlyallocated to three groups, representing threedifferent treatment regimens with pirlimycin,including 2-day (n = 21 cows, 31 mammaryquarters), 5-day (n = 21 cows, 32 quarters),and 8-day (n = 26 cows, 40 quarters). For allgroups, pirlimycin was administered at a rateof 50 mg of pirlimycin hydrochloride via in-tramammary infusion. A cure was defined asan experimentally infected mammarygland