SOMATIC-CELL COUNT PATTERNS IN PRINCE-EDWARD-ISLAND DAIRY HERDS

Pattern diagnosis (establishing a diagnosis of a herd problem based on the distribution of health events within that herd) is only possible if information about the expected, or 'normal' distribution is available. This study examined the distribution of somatic cell count (SCC) patterns in Prince Edward Island dairy herds. The main features were an overall prevalence of elevated counts (more than 200 000 cells ml-1) of 29%, a steady increase in prevalence estimates across the three age groups examined (lactation 1, lactations 2-4 and lactations 5+ ) and relatively constant prevalence estimates through the first 200 days of lactation. The overall new infection risk was 15% with similar age and stage-of-lactation patterns (as were observed for prevalence estimates). The overall elimination risk was 22% and it declined across all age and stage-of-lactation groups. Based on the variability of parameter estimates from a number of test dates, we recommend that at least 1 year's data (10-11 tests) be used to evaluate patterns in a dairy herd of 40-60 cows in this region of Canada.