Associations between somatic cell counts at calving or prior to drying-off and future somatic cell counts, in the remaining or subsequent lactation

Abstract

Composite milk somatic cell counts (CMSCC) from four separate datasets, containing 3338, 350, 1408 and 1404 herds, were used. All herds were enrolled in the Norwegian Dairy Herd Recording System (NDHRS). The aim was to investigate associations between CMSCC at calving or prior to drying-off and future CMSCC in the remaining or subsequent lactation. CMSCC was determined using Fossomatic 5000® cell counters (Foss Electric, Hillerød, Denmark) according to IDF recommendations (International Dairy Federation, 1984) and a natural logarithmic transformation of the CMSCC data (lnCMSCC) was performed. Results obtained were arranged according to parity and lactation stage and regression models and general linear mixed models were applied, the latter model to account for clustering between herds. The best associations between CMSCC at calving or prior to drying-off and future CMSCC in the remaining or subsequent lactation were found by using at least two CMSCC test days after calving or prior to drying-off. The geometric mean of the second and third or the first three CMSCC test days explained 50% of the variation in future CMSCC in first parity cows. This information was accessible at 151 days in milk (DIM) in bimonthly tested herds, and at 87 DIM for monthly tested herds. There was not a large difference using two or three single consecutive weighted CMSCC test days compared with the geometric mean of two or three CMSCC test days. Our findings indicate the need of using at least two CMSCC test days and, if only one CMSCC test day is used, it should be obtained after 14 d post-calving or preferably after 30 DIM.