The Veterinary Health Service ("Tiergesundheitsdienst", TGD), an organisation of veteri-narians and farmers, has been established for all federal states of Austria but Vienna. Here we present data concerning Upper Austrian dairy farms and results of bacteriological analysis of bovine quarter milk samples from the Upper Austrian TGD laboratory between 2011 and 2014, especially relating to prevalence and antibiotic susceptibilities of mastitis pathogens. Microbial isolates from quarter milk samples of Austrian cows were cultivated and identified using classical and advanced methods and tested for antibiotic susceptibility by the microdilution method. Generally, there has been a decrease in the number of milk suppliers and TGD farms in Upper Austria. Almost 10500 milk samples were analysed at the Upper Austrian TGD laboratory each year. Most commonly isolated udder pathogens in quarter milk samples were Staphylococcus aureus (26%), Streptococcus uberis (22%) and non-aureus staphylococci (15%). For many antibiotic agents we found high antimicrobial susceptibility of tested isolates. However, also an increasing prevalence of resistant strains against the beta-lactam antibiotics and the macrolide tylosin was detected. The mean proportion of multi-resistant isolates in staphylococci and streptococci isolates was below 5%. This longitudinal study acknowledges changes in the structure of Austrian dairies, the occurrence of mastitis pathogens and their antibiotic susceptibilities. Such adaptations could suggest the need for new types of farm management, together with preventive and treatment strategies.