The control of mastitis in herds affected by cow-associated microorganisms should be based on prophylactic means to reduce the new infection rate. In the cases of Streptococcus (Sc.) agalactiae and Sc. canis, control is aimed towards eradication of these pathogens on herd level, while the prevalence and, with that, the new infection by Staphylococcus (S.) aureus should be lowered to a minimum. When dealing with infections by S. aureus on herd level, usually extensive culling of infected animals and therapies to eliminate existing infections may be avoided, as long as the measures to control new infections are set into practice thoroughly. Of those, the most important ones are identifying infected animals, separating them from the uninfected ones, observing a corresponding hygiene at milking, disinfecting the teats after milking with accredited products and disinfecting clusters between milking. Except for surveys after appliance, no studies regarding the efficiency of S. aureus vaccines have been performed so far. When dealing with herd problems due to Sc. agalactiae, a similar approach as with S. aureus in order to reduce the new infection rate is recommended. However, this pathogen spreads more quickly than the other one, and so it is essential to reduce the control phase to a minimum. So, after identifying infected animals, a decision for therapy or culling must be made subsequently. If therapy fails, animals should leave the farm at once.