Direct Microscopic Somatic Cell Count

The direct microscopic somatic cell count (DMSCC) is microscopic count of the actual number of somatic cells in milk. A somatic cell is any biological cell forming the body of an organism. In dairy industry, the somatic cell count (SCC) is an indicator of the safety and quality of milk. Mastitis is an inflammation of the udder typically associated with microbial infection. The number of somatic cells increases in response to presence of pathogenic bacteria like Staphylococcus aureus, a cause of mastitis. Somatic cells (SC) are cells from the cow (predominantly white blood cells, otherwise known as leukocytes) that are normally present in milk. During most mastitis infections, the number of leukocytes present in the udder increases to help the cow, goat, ewe, camel, buffalo etc. to fight the infection. The SCC is quantified as cells per milliliter. General agreement rests on a reference range of less than 100,000 SC in ml for uninfected cows and greater than 250,000 SC in ml for cows infected with significant pathogen levels. There are several indirect and direct laboratory methods used for determination of somatic cells count in milk. Routine instrumental laboratory methods like flow cytometry have to be regularly calibrated using reference materials with a known concentration of somatic cells. The concentration of somatic cell count can be determined by reference microscopic method. The first microscopic procedure for examination of milk films was described in 1910 by Prescott and Breed. Staining of somatic cells was later modified by Newman, Lampert, Levowitz, Weber and other researchers. This microscopic method was processed into a normative form by the International Dairy Federation and later by International Standard Organisation. There are several possibilities to stain somatic cells. Somatic cells can be stained by dipping the dried smear on the slide in the modified Newman-Lampert methylene blue stain solution (cow's milk and ewe's milk) or methyl green-pyronin Y stain solution (goat's milk) or by mixing the milk in reagent tube with ethidium bromide stain solution (milk from all species). Subsequently, the microscopic slide with fixed smear and stained cells is examined using a microscope or epifluorescence microscope with immersion oil objective at magnification 500× to 1000×. Somatic cells are counted in several microscopic fields. Consequently, the somatic cells count is calculated using one of several mathematical formulas listed in international standard. The direct microscopic somatic cell count method is suitable for precise laboratory analysis of somatic cell in raw milk. However, this microscopic method has some limitations that may influence the results of analysis. This book contains the theoretical and practical information about this laboratory method.