ملخص
The present study contained total of 670 first lactation parity complete records of Friesian cows sired by 77 bulls, raised in south of Alexandria during the period from 1985 to 2014. These records were used to estimate genetic and phenotypic parameters by using MTDFREML for total milk yield (TMY), Daily milk yield (DMY), persistency (PER), Age at first calving (AFC) and calving to first service (CFS) in addition to establishment of many combinations of selection indices. Analysis of variance showed that sire and year of calving had significant effect on all studied traits (P< 0.01), however month of calving had significant effect on DMY and CFS only. Heritability estimates were 0.37, 0.27, 0.03, 0.38 and 0.11 for the previous traits respectively, the genetic correlations ranged from -0.92 to 0.94 and phenotypic correlation ranged from -0.25 to 0.64. Comparison between twenty-two selection indices showed that the maximum return can be achieved when applying the indices, I10 and I6 which includes three or four traits. These indices are simple and easy to construct. Therefore, it is recommended to apply selection at the end of first lactation based on these indices.