The present study was undertaken to find differences among the various genetic groups generated from crossing of Hariana (H), Holstein Friesian (HF) and Jersey (J) breeds (1/2 maintained during the period 1968–88). Effect of non-genetic factors viz., period and season of calving on age at first calving (AFC), service period (SP) and calving interval (CI) and the effect of the order of lactation and AFC on later two traits was analyzed. It was observed that the period, season, order of lactation and genetic group differences were significant (P0.01) for all the traits, except the effect of season on AFC. However, the effect of AFC on SP and CI was statistically non-significant (P0.05). There was no systematic trend over periods far service period in the three lactations. The average SP and CI were lower in seasons3 and 4 in comparison to seasons 1 and 2, while within these differences were non-significant. The average overall SP and CI were highest in first lactaion and significantly decreased in the subsequent lactations. Average AFC was highest in FH (1) and lowest in JH halfored Jersey halforeds had the lowest and the JFH had the highest SP and CI.