Hokkaido is a large dairy industrial district that produces approximately half of milk production in Japan. The Dairy Hygiene Unit in Hokkaido Research Station of the NIAH is a front-line base to carry out research and technological development focused on reducing and preventing bovine diseases such as mastitis, diarrhea, pneumonia and leukosis in dairy farms. On mastitis research, we have studied the onset mechanism of udder inflammation caused with bacterial infection. We have also been demonstrating the epidemiological characteristics of Staphylococcus aureus and mycoplasmas that caused bovine mastitis by using genome analysis. At present, we are developing mucosal vaccine, cytokine therapy and rapid detection of antibiotic resistant mycoplasmas against the bovine mastitis. In research on bovine leukosis whose prevalence is increasing in recent years, we have proposed a classification system based on histological and immunohistochemical findings, and are trying to find onset biomarkers of the leukosis. In addition, our unit is in charge of the fundamental operations for support of animal hygiene through diagnosis of animal diseases, technical training and technical dissemination.