Mastisis, an inflamatory disease of the mammary gland is of major importance in cattle in all milk producing countries. The development of mastitis is a dynamic process involving the external environment and management of the animals their susceptibility to the disease and the efficiency of their defence mechanisms once the disease has established. There are numerous factors associated with the disease which have been incriminated as predisposing factors. Many of these are really, just opinions, and consequently difficult to investigate experimentally. Even if this were possible, to investigate one in isolation from all the, rest would be unlikely to provide an unequivocal result. From the view of satisfactory statistical analysis, it, is impossible, without very great resources, to investigate management, hereditary and all other factors as a whole.