Regarding antibiotic resistance issue, antibiotic use has to be reduced. In the dairy sector, antibiotics are mostly used for the control and treatment of mastitis. We designed an exposed/non-exposed epidemiological study in Western France to evaluate effectiveness, strengths and weaknesses of an innovative training program: one classroom-training day, virtual classrooms, and an individual support with the farmer. Two groups of farmers addressed two different themes, depending on their herds’ udder health: (i) improvement of mastitis prevention during lactation for herds experiencing frequent clinical mastitis, and (ii) implementation of selective dry cow therapy for herds with good udder health, instead of implementing blanket dry cow therapy. We collected different sets of data to evaluate evolution of knowledge, practices of farmers, animal health and antibiotic use as well as their appreciation of the program. Some farmers appreciated the virtual classroom training method because it was flexible (frequency, timetable, etc.) and little time consuming. However, connection or computing logistic problems made the participation in the virtual classrooms difficult. For the “prevention” group, results also showed limited improvement of knowledge, perception and practices of farmers. Improvement of knowledge and perception was significant. Both exposed and non-exposed farmers did improve their practices of antibiotic use at dry-off, which could show a trend in the general population for the improvement of practices at dry-off, animal health and antibiotic use. The duration of the program (one and a half year) was relatively short to observe a change in practices, longer program could provide better results. Further insight should be provided with the results of “dry-cow” group.