Somatic cell count (SCC)

Somatic cells in milk are mostly white blood cells that enter the udder in response to infection. Their concentration, in cells per millilitre, is the standard measure of udder health. A count under 200,000 is generally taken to indicate an uninfected cow.

Because counts are strongly skewed, they are often converted to a linear score: the count is divided by 100,000, the base-2 logarithm is taken, and 3 is added. Each step of one point represents a doubling of the count.

Written for the 2026 edition of the library.