Abstract Mastitis is a common disease of dairy animals. The source of mastitis infection may be regarded as contagious or environmental. A wide range of pathogens including bacteria, viruses, fungi, and the toxins of these pathogens can cause the disease. Mastitis is generally associated with poor hygienic and husbandry practices. The primary reservoir of infection is the mammary gland. The infectious agent enters through the milk canal, interacts with the mammary tissue/cells and multiplies. Most contagious mastitis causing pathogens are spread during milking. Most other species are opportunistic invaders from the cow's environment.