Lipopolysaccharide challenge of the mammary 1 gland in cows induces nitrosative stress that 2 impaired milk oxidative stability 3 4 5 6

33 The aim of this work was to study the effects of mastitis 34 induced by intramammary lipopolysaccharide challenge on milk 35 oxidative stability, as well as to understand the underlying 36 biochemical processes that cause such changes. 37 Lipopolysaccharide challenge was associated with nitric oxide 38 burst from surrounding mammary epithelial cells and 39 consequently provoked nitrosative stress that was induced by 40 formation of NO2• from nitrite by lactoperoxidase. This response 41 was associated with ~3 fold increased formation of hazardous 42 compounds: nitrotyrosines, carbonyls and lipid peroxides. We 43 sustained the involvement of xanthine oxidase as a major source 44 of hydrogen peroxide. In consistent with previous findings, 45 catalase has been shown to have a major role in modulating the 46 nitrosative stress by oxidizing nitrite, to nitrate. The current 47 hygienic quality criteria cannot detect mixing of low-quality milk, 48 such as milk with high somatic cells and nitrite with high-quality 49 milk. Thus, developing of improved quality control methodology 50 may be found important for the production of high quality milk. 51 4 52