[Recurrent clinical mastitis in dairy cattle - importance and causes].

Clinical mastitis as a frequently recurrent event can cause substantive economic loss on dairy farms. The reason for recurrent mastitis can be either a persistent infection of the bovine mammary gland by a mastitis pathogen or a reinfection of a quarter or udder after bacteriological cure. The virulence properties of a mastitis pathogen and the cure odds of an individual cow determine the development of persistent infections. Clinical episodes may alternate with periods without symptoms in the course of persistent infections. Strategies to reduce cases of recurrent mastitis have to include improved treatment concepts and measures to decrease new infection rates. The present literature review summarises the knowledge of definitions, frequencies, causes and effects of recurrent mastitis.