EFFECT OF FREEZING ON SOMATIC-CELL COUNT OF QUARTER MILK SAMPLES AS DETERMINED BY A FOSSOMATIC ELECTRONIC CELL COUNTER

The objective of this study was to determine the effect of freezing an d the duration of freezing on somatic cell count(SCC) in milk samples from quarters with no signs of clinical mastitis. Effect was determine d by a fluoro-opto-electronic cell counter. Samples were frozen in a c ommercial freezer at approximately -20 degrees C. The milk samples wer e thawed at 1, 2, 3, 4, 7, 14, or 28 d. Another batch of samples was f rozen 1 d, thawed, frozen again for 1 d, and then thawed. The SCC was determined on the fresh samples and after any one of the freezing peri ods. On average, the SCC were lower after all freezing periods than th ey were before freezing. However, the difference in SCC before and aft er freezing was small and relatively constant on the natural logarithm scale. The decrease in SCC was larger with longer freezing periods. W hen SCC thresholds of 200,000, 250,000, and 500,000 cells/ml were used to predict infection, freezing appeared to have little impact on the sensitivity and specificity of diagnostic parameters. Therefore, SCC, as determined by a fluoro-opto-electronic cell counter, determined for frozen quarter milk samples can be used in mastitis control and resea rch programs.