Subclinical udder infection with Streptococcus dysgalactiae impairs milk coagulation properties: The emerging role of proteose peptones

Subclinical mastitis, caused by different bacteria with similar milk composition and somatic cell count, impairs milk quality and its products differently through increased release of deteriorative enzymes into the milk. Milk from glands infected with Streptococcus dysgalactiae was almost identical in gross composition to milk from uninfected glands. However, yogurt and cheese made from commingled milk from the infected quarters exhibited inferior texture compared to yogurt and cheese made from uninfected ones. Proteose peptone was size-fractionated by gel filtration and the various fractions of milk from the infected glands were added to uninfected milk. This study demonstrated for the first time that addition of certain fractions to milk from uninfected glands resulted in altered milk coagulation properties. It is hypothesized that the infecting bacteria influence the immune system of the udder, which then impairs the qualities of the milk from infected quarters that is conventionally used for manufacturing dairy products.