Abstract: This study aimed to determine the species distribution of pathogenic bacteria associated with clinical mastitis in dairy cows, and to compare the therapeutic effectiveness of combinative use of penicillin and streptomycin versus ′Woruite′ （a commercially available ceftiofur sodium preparation） alone in the treatment of clinical mastitis in dairy cows. A total of 100 dairy cows with clinical mastitis were selected and assigned into the following three groups a control group （n=4）, a ′Woruite′ treatment group （n=50）, and a combinative therapeutic group of penicillin and streptomycin （n=46）. Milk samples were collected from the experimental cows, and the bacterial isolation and identification were performed with traditional methods. Therapeutic effectiveness of the two medication regimens was clinically evaluated and compared. The most frequently isolated bacterial species was pathogenic staphylococci （37.0%）, followed by Escherichia coli （30.1%）, Klebsiella （18.3%） and streptococci (2.4%). Furthermore, some other bacterial species were also found, with total isolation rate of 12.2%. It was indicated that staphylococci are the dominant causative pathogenic bacteria in clinical mastitis of dairy cows. Both of the two medication regimens had good therapeutic effectiveness in treatment of clinical mastitis. The curative rate of the combinative therapeutic group of penicillin and streptomycin was 78.26%, which was significantly higher than that of the ′Woruite′ treatment group （66.00%）.

Key words: dairy cow, mastitis, treatment, diagnosis