Somatic cell counts and infection rates for cows of varying somatic cell count in initial test of first lactation.

Somatic cell counts (log, base 2) and rates of infection in first and subsequent lactations were examined by classes of somatic cell count in initial test day of first lactation to determine if cows with initially low counts were more at risk to subsequent mastitis infection. Classes of initial somatic cell counts were less than 100,000, 100,000 to 400,000 and greater than 400,000. Differences among initial classes in subsequent cell counts were small, but the initial rank of classes was maintained throughout the remainder of first lactations and in subsequent lactations. Differences among initial classes for rates of infection in first and subsequent lactations consistently favored low initial cell counts. Results gave no indication that cows initially low in cell count are at greater risk of subsequent mastitis infection.