Warm vs Cold Sampling of Raw Milk for Direct Microscopic Somatic Cell Counting

Standard Methods for the Examination of Dairy Products (1) requires that milk be sampled cold for analysis of both bacteria and somatic cells by the direct microscopic method. Preliminary observations made at Dairy Quality Control Institute, Inc. indicated that better precision in somatic cell counting could be obtained if milk was sampled at 38°C rather than 0-4.4°C. A study was undertaken to confirm preliminary findings. Three technicians made direct microscopic somatic cell counts (DMSCC) in triplicate on milk samples standardized to four different levels of counts. The grand average counts at the four levels of cells for cold vs warm milk sampling were, in thousands of cells per ml, 149 vs 154, 410 vs 416, 705 vs 697, and 1034 vs 1024. Grand average standard deviations for cold vs warm, respectively, at the four levels of count were 19 vs 17, 47 vs 42, 54 vs 50, and 69 vs 62. Thus, an improvement in precision of counting was observed at all four levels of somatic cells when raw milk is warmed to 38°C prior to sampling.