Cumulative milk yield at 305 days (MY-305) and somatic cell count (SCC) from the first to the fifth lactation of Holstein cows were analyzed in this study. Somatic cell count was logarithmically transformed to somatic cell score (SCS) that was then included in the model not only as a dependent but also as an independent variable. Year, season, and parity order all significantly affected the average SCS in this study. Data of the effect of SCS on milk yield showed significant losses on MY-305 because of the observed negative linear relationship between these two variables. Somatic cell score affected differently MY-305 from different parity orders with greater effect after the 3rd parity. Although clinical mastitis seems to cause greater economic losses, prevention and control of sub-clinical mastitis deserve more attention due to its greater prevalence leading to significant reduction on herd productivity.
dairy cattle; mastitis; milk yield; somatic cells
