In current study, 120 milk samples from cattle in husbandries around the city of Mashhad with clinical signs were tested. At first, samples were centrifuged. After that, one loop of pellet was taken end cultured on Blood agar and Mac Conkey Agar. Plates were incubated at 37º for 24hrs. The growth of bacteria was analyzed after incubation period. The bacteria from plates were observed macroscopically and also microscopically. Catalane, oxidase tests and gram stain were conducted to distinguish the family of bacteria. Also differential tests were performed for detection of species. From 120 samples, 36, 4, 2, 8 and 10 samples were determined as Streptococcus. agalactiae; Streptococcus. dysgalactiae; Staphylococcus .aureus; E. coli and Yeast respectively. Sixty samples were negative. S .agalactiae (%10); S .dysgalactiae (%3/3) and S .aureus (%1/6) cause mastitis in dairy cattle respectively. Yeast (%8/3) and E .coli (%6/6) cause mastitis as environmental factors. This study revealed that S. agalactiae is the main pathogen responsible for mastitis. Also, environmental pathogens may be considered as the second factor. By performing correct management on the herds, it is possible to control mastitis caused by pathogen and environmental bacteria.

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