RELATIONSHIP BETWEEN MINIMUM INHIBITORY CONCENTRATIONS OF STAPHYLOCOCCAL ISOLATES OBTAINED FROM MAMMARY GLANDS OF DAIRY HEIFERS AND OUTCOMES OF PREPARTUM MASTITIS TREATMENTS

摘要

In recent years, studies have indicated that the prevalence of IMI in heifers can be as high as 97% (Trinidad et al., 1990). Intramammary infection in heifers is often caused by coagulase-negative Staphylococcus spp. (CNS) (Oliver et al., 1992; Fox etal., 1995; Nickerson et al., 1995). Intramammary treatment of prepartum heifers is generally considered to be effective in reducing the prevalence of IMI, may result in a reduction of SCC, and in some cases has been shown to increase milk production inthe subsequent lactation (Trinidad et al., 1990; Nickerson et al., 1995; Oliver et al., 2003). Antimicrobial susceptibility testing is commonly used to help select antibiotics for treatment of mastitis. The ability of in vitro susceptibility tests to predict bacteriological and clinical outcomes of intramammary therapy in lactating cows has been questioned (Owens et al., 1997; Shpigel et al., 1998; Constable and Morin, 2003; Hoe and Ruegg, 2004). No studies have been published investigating the relationship between results of in vitro susceptibility tests and outcomes of prepartum intramammary treatments of dairy heifers. The objective of this study was to determine the relationship between the minimum inhibitory concentration (MIC) of staphylococcal isolates obtained from mammary glands of dairy heifers and outcomes of intramammary treatments administered during the prepartum period.