Estimation of somatic cells in milk using membrane filter separation and DNA determination with diphenylamine.

A diphenylamine-DNA method of estimating somatic cell concentration in milk was studied in two separate trials. Trial I involved 68 bulk milk samples and a comparison of detergent and centrifuge procedures for separation of milk fat prior to estimation of somatic cells. Membrane filters of 3μ-pore size were used to concentrate cells. Color developed with diphenylamine was measured in a spectrophotometer. The detergent preparation was superior to centrifuging, as judged by correlation coefficients between the direct microscopic cell count (DMSCC) and optical density (OD) of 0.93 and 0.82, respectively, for the two methods. Coefficients of variation of duplicate optical density readings were 9.4 and 16.7 for the detergent and centrifuge methods, respectively. Regression equations revealed a linear relationship between OD and DMSCC for the detergent, but a curvilinear relationship for the centrifuge procedure. In Trial II, 40 bulk milk samples were analyzed with an improved procedure involving detergent prep...