Bovine mastitis has long been thought to be the result of a host-pathogen interaction. However, microbiota is now considered as a key player of this infectious disease process. This talk presents an overview of our research on the role of milk and mammary gland microbiota on mammary health and the opportunities it offers for a more sustainable management of dairy cows health. The role of milk and mammary gland microbiota on mammary health was first highlighted by exploring these relationships either before or after mastitis events, i.e. at distance from the infectious episode. Teat cistern microbiota (collected in foremilk) was found to be related to the history of animals with regard to mastitis. Besides, using a switch from twice- to once-daily milking (ODM) to trigger an udder perturbation in initially healthy quarters of cows, a temporal relationship was reported between initial teat cistern microbiota and the immune response and mastitis development following transition to ODM. In order to identify determinants of milk microbiota composition, cows with different scores of susceptibility to mastitis were used to explore the microbiota in various body sites throughout lactation. Microbiotas from milk, mouth, nose and vagina were specific and evolved throughout lactation. Interestingly, an important intra-animal sharing of microbes between anatomic sites was reported, whereas inter-animal microbial sharing was limited, suggesting a host regulation of bovine microbiota, including a slight role of the score of susceptibility to mastitis on milk microbiota. Within mammary gland microbiota, lactic acid bacteria (LAB), used as probiotic, showed promise for mastitis prevention. In vitro, LAB were able to compete with pathogens for epithelium colonization and exhibited immunomodulatory properties. A promising LAB candidate was recently evaluated in vivo through the assessment of its microbiological, immune and physiological impact on the mammary gland, following post milking application on teat skin. The safety of such topical application was confirmed, opening the avenue for the development of new prophylactic strategies.