From the NMC Newsletter "Udder Topics", August, 1999

Bulk tank SCCs (BTSCC) are a primary measure of udder health and are a function of the percentage of quarters infected by major pathogens in a dairy herd. Research conducted in 1982 (Relationships of bulk tank somatic cell counts to prevalence of intramammary infection and to indices of herd production. Eberhart, R.J., L.J. Hutchinson, and S. B. Spencer. J. Food Prot. 45:1125) showed a linear relationship between BTSCC and the percent quarters infected with major pathogens. For bulk tank SCC of 200,000, 400,000, 750,000, and 1,000,000 cells/ml, the percent quarters infected would be 6.2%, 12.8%, 24.3%, and 32.6%, respectively.

Since the current SCC regulatory limit in the U.S. is 750,000 cells/ml, milk is still accepted from herds in which approximately 25% of quarters are infected by major pathogens. Should this be considered "normal" milk?