The current standard solutions for somatic cells used for calibration of electronic somatic cell counts as reference material in raw milk are preserved with bronopol, boric acid, sodium azide, or potassium dichromate, and have a shelf-life of only up to 6 days at 4 ± 2℃. In the present study, a set of somatic cell standard solutions (SCSS) with a stability of 5 months for calibration of electronic instruments was developed. Somatic cells collected from cow’s milk and stored in a bulk tank at a dairy plant were treated with 10% formaldehyde in order to improve stability, and then separated by centrifugation. The resulting somatic cell suspension was preserved with glycerin, thimerosal, and dimethyl sulfoxide, and diluted in 3% processed skim milk solution ranging from 200,000～250,000 (low level), 350,000～ 450,000 (medium level), and 550,000～650,000 (high level) cells/㎖. Each SCSS was verified by direct microscope somatic cell counting (DMSCC), C-reader, and commercial standard samples. The average somatic cell count determined by DMSCC was 248, 214, 226 × 103 cells/㎖, 436, 382, 420 × 103 cells/㎖, and 612, 595, 609 × 103 cells/㎖. The coefficient of variation representing the repeatability of DMSCC decreased as the number of cells increased, and was <10.0% in almost all SCSS samples (range 4.6～7.1%). No statistically significant difference in somatic cell concentration was observed after storage at refrigeration temperature (2～6℃) over a period of 22 weeks (5 months). The stabilized SCSS may be useful as a reference material for determination of somatic cell count and quality control in testing of bovine raw milk.

ABSTRACT
 Introduction
 Materials and Methods
  1. Preparation of SCSS
  2. Verification of the SCC in SCSS
  3. Evaluation of the shelf-life stability of scss by automaticESCC
  4. Statistical analyses
 Results and Discussion
  1. Repeatability of the each standard somatic cell solution
  2. Comparison of ESCC instruments used for analyzingSCSS stability
  3. Analysis of shelf-life stability of SCSS
 References

• Jin San Moon(Animal, Plant and Fisheries Quarantine and Inspection Agency)
• Keum-Chan Jang(Animal, Plant and Fisheries Quarantine and Inspection Agency)
• Suk-Chan Jung(Animal, Plant and Fisheries Quarantine and Inspection Agency)
• Yi-Seok Joo(Animal, Plant and Fisheries Quarantine and Inspection Agency)
• Ji-Ho Kim(Animal, Plant and Fisheries Quarantine and Inspection Agency)
• Sung-Hwan Wee(Animal, Plant and Fisheries Quarantine and Inspection Agency)
• Hye Cheong Koo(College of Veterinary Medicine and BK21 Program for Veterinary Science, Seoul National University)
• Yong Ho Park(Animal, Plant and Fisheries Quarantine and Inspection Agency, College of Veterinary Medicine and BK21 Program for Veterinary Science, Seoul National University) Correspondence