A total of 2714 records of average daily milk yield and 2035 records of average milk yield per day of calving interval belonged to Holstein cows maintained at Nasr and Esihaqi dairy cattle over period from 1995 to 2001 were analyzed. The aim is to evaluated sires and daughters genetically according to average daily milk yield and average milk yield per day of calving interval before adjusting for fixed effects and to estimate heritability and repeatability for two traits. The General Linear Model within SAS program (2001) was used to investigate the effects of some factors (season and year of calving, parity, age at first calving, herd and length of lactation) as groups, on average daily milk yield, and also to study the same effects except length of lactation which was changed to length of calving interval on average milk yield per day of calving interval. Component of variance for the random effects was estimated by RMEL method. The Harvey (1991) program was also used to estimate BLUP values for sires and daughters. The overall means of average milk yield was 11.81 kg and the effect of all fixed factors were significant (p < 0.01) except age at first calving which was not significant .whereas means of average milk yield per day of calving interval was 9.24 kg and all fixed factors were significant ( p < 0.01).
The heritability and repeatability for average milk yield were is 0.17 and 0.23 respectively, the same parameters for average milk yield per day of calving are 0.14 and 0.23 respectively. There is a wide range in BLUP values of average milk yield estimated %ranged from- 2.37 to 1.33 kg for sires and -4.32 to 4.38 kg for daughters Whereas BLUP values of average milk per day of calving interval ranged from – 0.51 to 1.04 kg for sires and –3.86 to 5.14 kg for daughters.