A study was conducted on 2102 records of 808 crossbred cows of 12 genetic groups with half and three fourth inheritance (two exotic breeds) and their inter-se crosses involving Holstein Friesian (F), Brown Swiss (B) and Jersey (J) with Hariana (H) breed. Data generated over a period from 1968 to 1993 on the herd maintained in the Department of Animal Breeding of this University were analyzed with the objective to study the genetic group differences and factors affecting age at first calving (AFC), service period (SP) and calving interval (Cn) in the first three parities. The genetic group differences were significant for all the traits except third SP and CI. The period of calving significantly affected alla the traits except 2nd CI and 3rd SP. The effect of season of calving was non-significant for all the traits except 3rd CI. Period-season interaction was non-significant for all the traits. Genetic group comparison indicated that among half breds, jersey crosses had better reproduction in terms of shortest AFC, SP and CI. Among the three-fourth-breeds, the FJH group had the lowest AFC and JFH group the lowest SP and CI for all the three lactations. Among inter-se-crosses, JFH (U) had lowest average AFC, while BFH (I) the lowest SP and CI.