Preparation and Use of Somatic Cell Count Samples (SCCS) for Comparison of Milk Somatic Cell Counting Methods

Somatic cell count samples (SCCS) for use in comparison of milk somatic cell counting methods were prepared from the cell sediment deposited in a creamery milk separator. Bovine milk somatic cells were resuspended from the sediment, and serial cell dilutions were prepared in bronopol-preserved milk diluent. Over a 1-year period, sets of SCCS were prepared each month and sent to milk-testing laboratories in the U.S.A., Canada and Europe, and counted by the methods in use at those Laboratories: (a) direct microscopic somatic cell count (DMSCC), (b) Fossomatic counter and (c) Coulter counter. Cell counts were normalized to eliminate the effect of month to month variation in the cell content of the SCCS. Counts obtained by the three methods were similar, although Coulter counter results tended to be lower, and significantly lower (P< 0.05) in SCCS with cell counts greater than 700,000 cells/ml than those counts by the other two methods. The effect of shipping on SCCS stability was assessed for SCCS samples sent to and returned from other laboratories, and counted by the Fossomatic method on their return. Counts were similar before and after shipping, except that results for SCCS with cell counts greater than 1,000,000 cells/ml were significantly higher (P<0.05) after their return.