Effects of freezing on the viability of nine pathogens from quarters with subclinical mastitis

Milk samples from 45 quarters containing mastitis pathogens were collected from lactating cows to determine the viability of those pathogens after freezing. An initial bacteria count was conducted, and samples were divided into 2-ml portions and frozen. Weekly bacteria counts were conducted for 6 wk. Viability after freezing was determined on five isolates of nine bacterial species: Staphylococcus aureus, Staphylococcus hyicus, Staphylococcus chromogenes, Staphylococcus xylosus, Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis, Corynebacterium bovis, and Escherichia coli. Bacteria counts were converted to logarithm base 10, and analysis of variance was conducted to determine alterations in viability over the 6-wk period. Freezing of quarter milk samples for 6 wk did not affect viability of any of these pathogens.