An effect of mammary gland infection caused by Streptococcus uberis on composition and physicochemical changes of cows' milk.

An effect of mammary gland infection caused by Streptococcus uberis on the changes in cows' milk composition and its physicochemical properties was examined. The study was conducted in the herd of Slovak Pied breed cattle (with a share of HF blood), in 2nd and 3rd lactation, after 4th month of milking. Milk samples were collected from a quarter milking. The samples were subjected to microbiological analysis, basic milk composition, total bacteria count, somatic cell count and physicochemical properties were examined. Also analyses of protein fractions share and fatty acids profile were conducted. An effect of bacterial infection of the mammary gland bring an increase (P<0.01) in somatic cell count was observed in this study. Milk samples contaminated with S. uberis were characterized by higher (P<0.05) total bacteria count and total protein compared to milk samples collected from non-infected mammary gland. The level of κ-casein was significantly (P<0.05) decreased in cows with subclinical mastitis caused by S. uberis. Significant (P<0.05) reduction in the share of C13:0 acid, and an increased level of C18:0, C18:1n7t and CLA were observed in milk contaminated with S. uberis compared to healthy cows' milk. It should be concluded that S. uberis causes the increase in total bacteria count, SCC and the decrease in κ-casein level, which significantly affects deterioration of technological quality of cows' milk.