Mastitis is a frequent and costly disease in dairy cattle. It has a negative impact on animal welfare, milk quality and increased use of antibiotics. The objective of this poster is to analyze the effect of polyvalent mastitis vaccine (STARTVAC®) against Staphylococcus aureus (S. aureus), non-S. aureus Staphylococci (NAS), Escherichia coli (E. coli) and coliforms vaccination in commercial dairy farms in the Netherlands.