English abstract
The purpose of our study was to determine if variation in milk yield at later stages of lactation can be explained by expressions of early lactation somatic cell score (SCS) and if the prediction of future yield within lactation can be improved by including SCS among the predictors. Three data sets (n >600,000 each) were: milk yield with sample days near 20. 50 and 140. Stepwise regression was used requiring F statistic (P <.01) for any SCS variable to stay in the model. Separate analyses were run for 12 combinations of four seasons and first three parities for each data set. Selection of SCS variables was not consistent across seasons or parities. Coefficients of determination (R2) ranged from 54 to 74% with higher values for higher days in milk (DIM) and earlier lactations. The inclusion of SCS expressions in the prediction equations improved R2 by <1%. SCS was associated with milk yield on sample day, but the association was not strong enough to improve the prediction of future yield when other expressions of milk yield were taken into account.
