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Variation of Estimated Numbers of Milk Somatic Cells Stained with Wright's Stain or Pyronin Y - Methyl Green Stain¹

Department of Dairy, Michigan State University, East Lansing

ABSTRACT

The purpose of this research was to compare the variation of estimated numbers of somatic cells in milk stained with pyronin Y - methyl green with that of cells stained with Wright's stain. Pour Breed smears were made from each of 27 milk samples, including 14 mastitic samples. Two smears were stained with Wright's stain and two with pyronin Y - methyl green stain. The averages obtained (x 10⁴) from duplicate determinations of agranulocytes, granulocytes, leucocytes, epithelial cells, and total somatic cells were 8, 306, 314, 64, and 378, respectively, for Wright's stain; and 15, 344, 359, 63, and 422, respectively, for pyronin Y - methyl green stain. Although the epithelial cells were equally recognizable in the two stains, a considerable portion of the leucocytes was masked by the background of the smears prepared with Wright's stain.

The pyronin Y - methyl green stain resulted in an approximate 25% reduction in smear variance and in an approximate 50% reduction in count variance when compared with Wright's stain. Expected 95% confidence intervals for determinations of mean cell numbers were computed from the estimated variance components with varying numbers of smears and counts. These values generally indicate that one should make approximately 200 smears from a milk sample to obtain a 95% confidence interval of approximately 50 x 10⁴ cells per milliliter of milk. These data suggest that ways of reducing the error variance should be investigated.

¹ Journal Article 3094 from the Michigan Agricultural Experiment Station.