Introduction and aims: Bovine mastitisis an inflammation of the mammary gland generally due to an infection. Itis responsible for considerable economic losses in dairy farms. Preventive and curative strategies that mainly rely on antibiotic therapies are not totally effective and contribute to antibiotic resistance dissemination, prompting the need for alternative or complementary strategies. We previously established a link between teat cistern microbiota composition and bovine mastitisin quarters which had different histories regarding mastitis[1].In thisstudy, to further decipher the relationships between teat cistern microbiota and immune and microbial responses, a switchfrom twice-to once-daily milking (ODM) was used to trigger an udder perturbation. Material and methods: Aswitch to ODM was used in 31initially healthy quarters of dairy cows. Immune and microbial responsesincluding determination of teat microbiotawere monitored just prior to the transition (day 0), and 3 and 14 days following transition to ODM. Results and discussion: Atemporal relationship was reportedbetween initial teat cistern microbiota composition and richness, the immune response to ODM, and mastitis development. Quarters with a low initial microbiota richness and taxonomic markers such as Bacteroidetes and Proteobacteria were associated with a higher rate of mastitis during ODM. Quarters with a higher richness and taxonomic markers such as Firmicutes, Bifidobacteriumand Corynebacteriumdisplayed early inflammation following transition to ODM but without developing mastitis (no infection). Short-term evolution of microbiota indicates that microbiota with a higher initial richness were more strongly altered by transition to ODM, with notably the disappearance of rare OTUs. Microbiota modifications were associated with an early innate immune system stimulation, which, in turn, may have contributed to the prevention of mastitis development[2].These results suggest a role of the bovine teat microbiota composition and richness in the immune response of the mammary gland during perturbations such as transition to ODM or pathogen entrance. They invite us to considerstrategies that can preserve teat microbiota diversityandtaxa associated to a healthy status for the design of next-generation probiotics.