The current study examines the prevalence and seasonal occurrence of major bacterial pathogens and effect of different

antibiotics on bacteria isolated from 935 bovine mastitic milk samples in northern region of India for characterization and

culture sensitivity against different antibiotics. A major proportion of mastitis samples- 412 (44%) were recorded during rainy

season, while, samples in equal shares, 276 (28%) and 247 (27%) were documented in winter and summer seasons, respectively.

Out of total 935 mastitic milk samples, 889 (95%) samples showed microbial growth, while, 46 (5%) samples were found

negative for any bacterial growth. Among total isolated bacteria, Gram positive- 471 (53%) shared a major proportion, followed

by Gram negative 341 (38%), while a small part of 53 (6%) and 24 (2%) samples yielded mixed unidentifi ed cultures and Candida species, respectively. In antibiogram study, gentamicin (91.21%), ciprofl oxacin (89.60%), enrofl oxacin (88.28%) and tetracycline (71.30%) were found to be highly effective antibiotics, while, penicillin (86%), colistin (83.30%), cloxacillin (78.62%), amoxycillin (70.71%) and ampicillin (62.51%) showed least effect against both Gram positive and negative bacteria. The present study showed that there was close association between season, bacterial pathogens and occurrence of of bovine mastitis. Overall, Staphylococcus spp., Streptococcus spp. and E. coli contributed as major mastitis dweller bacteria.