Abstract: Objective: Test day milk average somatic cell count is a frequently used indirect indicator of infectious status of mammary glands. Therefore, the aim of this study was to compare the efficiency of using cumulative milk yield or test day milk yield as a criterion to improve milk production based on measures of somatic cells in milk. Methodology: This study was carried out during the period extended from year 2008-2010 on 1739 dairy records for 858 cows by 86 sires US Holstein from Dina farms situated about 80 km in Cairo-Alexandria desert road. Variance components, heritability estimates, genetic, phenotypic and Spearman’s rank correlations between breeding value for somatic cell score and both cumulative milk yield and test day milk yield in first six months of lactation period were analyzed by using a multi-trait animal model analysis. Results: According to the results of the study, there is a direct relationship between somatic cell count score and somatic cell count, the highest score (9th) was observed when somatic cells being 8517.36 cells mL–1. Conversely, test day milk yield was inversely affected by somatic cell count score, the highest test day milk yield (50.63 kg) was obtained with the lowest score of somatic cells. Additive genetic variances based on somatic cells were low compare to permanent environmental variances. Thus, the possibility of improving these traits is small and takes a long period of time. Conclusion: Finally, it could be concluded that test day milk yield has the possibility of selection for milk yield based on somatic cell measures before the end of lactation mainly at the first two thirds of lactation season enabling inclusion of cows with incomplete lactations in the genetic evaluation which may resulted in improving generation interval, intensity of selection and enhance the genetic progress.