Abstract: In order to clarify the major pathogenic bacteria and the incidence of cow subclinical mastitis in Dalian area,256 cows of the different lactation time were investigated from different areas of Dalian. The major pathogenic bacteria were isolated and identified from the milk samples of the subclinical mastitis in dairy cows,and the susceptibility to antibiotics for the major pathogenic bacteria was tested. The results showed that the positive rate of subclinical mastitis was 65.63% and the mammary region positive rate of subclinical mastitis was 51.95% in the tested cows; Staphylococcus aureus,Streptococcus and Escherichia coli were the major pathogenic bacteria causing cow subclinical mastitis,and the cases of cow subclinical mastitis caused with this three kinds of pathogenic bacteria were 83.33%; the hypersensitive antibiotics to the major pathogenic bacteria of cow subclinical mastitis were screened by the drug sensitivity test in vitro,these hypersensitive antibiotics could efficiently treat cow subclinical mastitis in Dalian area.

Key words: cow; subclinical mastitis; pathogenic bacteria; isolation and identification; drug sensitivity test