Epidemiologic considerations in reporting herd somatic cell counts

The reporting of herd summaries of individual cow somatic cell counts (SCC) differs between the 9 Dairy Records Processing Centers. Estimates of central tendency and frequency distributions are the most commonly used herd summary statistics for SCC. Analyses of the frequency distributions are less widely available. Potential uses of herd SCC are: to measure one aspect of herd milk quality; to estimate the prevalence of mastitis; to analyse mastitis patterns within the herd; and to investigate new areas for mastitis control research. The best available methods for these applications appear to be: bulk tank SCC or weighted arithmetic means for gauging milk quality; frequency distributions for estimating mastitis prevalence; analyses of frequency distributions or mean linear score by lactation and stage of lactation for identifying mastitis patterns within a herd; and frequency distributions or estimated incidence rates, adjusted for differences in age and stage of lactation, for investigating new areas for mastitis control research..