Introduction

Lago et al. (2011a and 2011b) reported that the treatment of only clinical mastitis (CM) from which gram-positive bacteria was isolated resulted in a significant reduction in antibiotic use, but no significant differences in short and long-term outcomes. However, one potential limitation of the study was that the label of the intramammary (IMM) antibiotic administered did not include efficacy claims against gram-negative bacteria. Intramammary antibiotic preparations, one containing ceftiofur and the other containing hetacillin potassium are currently approved in the United States with a label that claims efficacy against CM in lactating dairy cattle associated with E. coli. This manuscript objective is to compare antibiotic use, clinical and bacteriological outcomes for selective treatment of gram-positive