Size Referenced Electronic Leukocyte Counting Threshold and Lysed Leukocyte Size Distribution of Common Domestic Animal Species

Using a single channel electronic cell counter and attached particle size analyzer, leukocyte size distribution histograms were determined on canine, feline, bovine, and equine blood diluted with chloride-based diluent and treated with a conventional stromatolysin. Histograms were usually unimodal, but a few were bimodal. Mean values for mean lysed leukocyte particle volume were 49.2, 51.1, 55.4, and 65.0 fl for canine, feline, equine, and bovine blood, respectively. From inspection of histograms, a lower threshold of 30 fl referenced to latex spheres was interpreted to be appropriate for counting leukocytes of these four species simultaneously. Debris below the threshold was seen in many samples and was usually separated from the leukocyte population by a valley touching the histogram baseline at the threshold channel. Debris resulted in a visually detectable threshold failure by extending considerably into the leukocyte size range in 9% of feline, 9% of canine, and 7% of bovine samples. It is recommended that careful establishment of the lower counting threshold will minimize frequency and severity of leukocyte count error associated with failure to exclude debris.

Comparison of the Automated with the Semi-Automatic Coulter Counter Method and the Direct Microscopic Somatic Cell Count (DMSCC) on Raw Milk Samples1

The automatic Milk Cell Counter (MCC) and semi-automatic electronic cell counter (ESCC) of Coulter Electronics were compared with each other and with the direct microscopic cell count (DMSCC) on raw milk samples with various cell counts. The average DMSCC count on 241 samples of milk with Wisconsin Mastitis Test (WMT) results of 22 mm and higher was 55,000 cells/ml above the average MCC count when calibrated to a 4.4-μm minimum particle diameter. This difference is statistically significant at the 1% level. On 24 different raw milk samples of widely varying somatic cell count analyzed in replicate six times per sample, the standard deviations for replicate samples were 34,300, 34,900 and 136,000 for the MCC, ESCC and DMSCC, respectively. For these tests, the MCC had been calibrated to a 4.3-μm minimum particle diameter. The average difference between counts by the MCC and ESCC methods was only 6080/ml, but this was statistically significant at the 5% level. The average MCC count with the equipment set at 4.3-μm minimum particle diameter was 58,000 above the average DMSCC count.