The article examines the research on the etiology of mastitis in cows. Mastitis is a widespread disease of dairy cows. Diagnostic tests were performed to study the extent of mastitis spread in lactating cows. The main reason for the destruction of dairy cows with mastitis is not the benign feeding affected by mold fungi. Tests of feeds were selected to detect the level of contamination by microorganisms.Key words: milk, mastitis, microorganisms, etiology.The quality of the produced milk is affected by the sanitary condition of farms, the presence of cows, sick with mastitis and endometritis, the state of the technology of primary processing and storage of milk [1,2,3,4].Due to inflammation of the udder, the productivity, sanitary quality of milk decreases, premature culling of cows due to hypothalaxia and atrophy of the udder occurs, the disease incidence of newborn calves increases (V.A. Parikov, 1990; N.G. Gasanov, 1990; L.D. Demidova, 2002; L.G. Roman, 2010; A.M. Semivolos, 2013; A.Ya. Batrakov, 2014; N.T. Klimov, 2014; Avdeenko, 2009 Avdeenko, , 2015.The resistance of cows to mastitis is of great importance for obtaining high-quality milk [5,6].In the emergence and spread of diseases of the mammary gland in cows, factors that reduce the resistance of the mammary gland and the organism as a whole play an important role (N.A. Sapozhnikova, 1992; V.I. Slobodyanik, 1994 V.I. Slobodyanik, -2000 I.A. Rodin, 2002) on the background of which the pathogenic and conditionally pathogenic microflora manifests its action (V.M. Kartashova, A.I. Ivashura, 1988; V.M. Ivchenko, 1991; G.N. Kuzmin, 1995; V.M. Bagmanov, 2005; S. Janossi, Z. Baltay, 2004; D.P. Berry, 2005; V.S. Avdeenko, 2009; V.N. Filpot, Sh.S. Nickerson, 2012).Much depends on keeping of animals in primary farms, unsatisfactory condition of which leads to contamination by pathogenic microorganisms in the process of milking.The most significant climatic factors that affect the composition and properties of milk are the temperature and humidity of the air. Violations of the microclimate parameters reduce milk yield and the mass fraction of fat in milk [7].