Relationships of Bulk Tank Somatic Cell Counts to Prevalence of Intramammary Infection and to Indices of Herd Production1

Abstract

Linear regressions and correlations between bulk tank somatic cell counts and (a) prevalence of intrammary infection (n = 80), (b) test day average daily milk and fat production per cow (n = 85), and (c) rolling herd average milk and fat production per cow (n = 83) were determined. The correlation coefficient between bulk tank somatic cell count and prevalence of infection was + . 77 and the coefficient of determination was .59; prevalence of infection was thus the major determinant of bulk tank somatic cell count. Highly significant negative correlations were found between bulk tank somatic cell counts and indices of herd production.