Preparation, Use and Evaluation of Standards Developed for Simultaneous Monitoring of Coulter and Fossomatic Electronic Cell Counting Instruments in Ontario

Special standards for Somatic Cell Counting (SCC) were developed at the Central Milk Testing Laboratory in Guelph for Ontario laboratories performing the tests. One laboratory used a Coulter milk counter for composite herd samples, two laboratories used five Fossomatic counters for cow samples, while the fourth used a Coulter counter for research purposes. Standards were prepared at low, medium and high count levels from fresh herd milks containing somatic cells near levels of 100,000, 500,000 and 1,000,000/ml. As the lifespan of the suspensions of somatic cells was three months, they were prepared in sufficient quantities to test daily for 3 months, and to be used throughout the day for calibration maintenance. The actual counts in the standards were established by direct microscopic somatic cell count (DMSCC) performed in two laboratories simultaneously with exchange of slides. Counts were re-confirmed every week by the same DMSCC procedures. The standards are suitable for initial calibration, daily calibration maintenance, daily instrument performance appraisal and trouble-shooting. In daily use each laboratory tests each standard five times each morning on each instrument. The same vials are used throughout the day, every 0.5 h for appraisal of continuous calibration and instrument function. The mean and standard deviations of standards are determined and compiled for each day.