The choice of dry cow antibiotics should be based on clinical efficacy studies. The choice also depends on the sensitivity pattern of S. aureus, and the expected length of the dry period. There are many quarter, cow and herd factors that influence efficacy of dry cow therapy. These factors include somatic cell count, front-versus-hind quarter, age, and the number of infected quarters in a cow. Nutrition of cows at the end of the lactation and hygienic conditions on the farm and off are also important. The effect of extra treatments at dry off are questionable.