Use of the Fossomatic Somatic Cell Counts in a Mastitis Control Program ¹

The Fossomatic determination of somatic cells present in individual cow milk samples was instituted in the Virginia Dairy Herd Improvement testing program in June, 1976. During the first 6 months the average count was 449,060 cells/ml for 113,735 observations. The average percentage of cows according to ranges in cell counts was: under 150,000, 47.9%; 150-400,000, 25.8%; 400-800,000, 12.5%; 800-1,500,000, 7.2%; and over 1,500,000, 6.6%. The percentage of cows with less than 150,000 cells/ml was reduced for September, 1976. On a herd basis, 66% averaged less than 500,000 cells/ml, 30% between 500 to 1,000,000, and 4% exceeded 1,000,000. The percentage of herds with less than 500,000 cells/ml decreased from June to September, 1976 but increased in October. Quarters infected with primary pathogens were estimated by Westgarth's equation to be 10.4% resulting in a calculated 5% reduction in total herd milk production. Procedures are described which would assist dairymen in the interpretation of somatic cell counts.