Effect of Several Factors on Total and Differential Counting of Somatic Cells in Farm Bulk Tank Milk.

Samples from approximately 1000 bulk tanks from widely separated areas of Ontario were examined over a period of 1 year. Total and differential somatic cell content was estimated electronically. A high degree of reproducibility was shown both in total cell count, and percent of cell volume in specific size ranges (channels) determined with a Coulter Model TA electronic counter. Use of a single count per dilution made little practical difference as compared to using the average of two counts per dilution. There were no significant differences between cell count means and cell volume percentages in channel 8 (cells from 89.2 to 178.3 μm3) from 24- and 48-h-old samples from either fluid or industrial shippers. There was a small significant difference in both measurements in duplicate samples shipped 275 miles before and after formalin fixation, and the cell volume in channel 8 was markedly reduced by shipping samples the same distance. Data from a small group of herds which were quarter sampled and submitted for mastitis laboratory diagnosis indicated the possibility that the percentage of cell volume in channel 8 found in bulk tank milk may be a better indicator of infection incidence in a herd than the total cell count alone.