Bovine mastitis is the most impacting disease of dairy industry, and it is characterized by a complexity of causal agents, which have revealed a geographical variation among regions and countries. The mastitis-related pathogens have been traditionally classified as contagious or environmental, based on habits of the microorganisms and transmission routes. In addition, the severity of mammary infections has been associated with the virulence of the pathogens, and immune and nutritional status of the hosts. Considering this scenario, we investigated the etiological nature, clinical severity scores, and days in milk (DIM) data in 4,273 clinical cases of bovine mastitis among ten large-dairy farms located in the Southeast region of Brazil. Streptococcus dysgalactiae (283/4,273=6.6%), Escherichia coli (190/4,273=4.4%), Prototheca spp. (112/4,273=2.6%), and Streptococcus uberis (95/4,273=2.2%) were the predominant pathogens isolated, all from the environmental origin. Among 4,273 clinical cases, clinical gravity score was available in 43.8% (1,871/4,273) animals. From these, 69.8% (1,306/1,871), 27.3% (510/1,871) and 2.9% (55/1,871) were scored as mild, moderate, and severe, respectively. Most of isolation of pathogens were observed in the first 100 days in milk, and their clinical severity scored as mild (3,612/4,273=84.5%). Our results contribute to the etiological identification, clinical severity scoring, and milking aspects of bovine clinical mastitis in dairy farms with a history of clinical mammary infections.