This study was carried out to evaluate the reproductive performances of Iranian dairy cattle at Tehran and Ghazvin Provinces. Reproductive traits included: calving interval, days open, and service per conception. A total of 2500 cows were used in this trial. Some effective factors were collected by the Animal Breeding Center of Iran from 1993 to 1998. Cows were classified into seven groups according to the age at calving (22 to 23, 24 to 25, 35 to 36, 47 to 48, 59 to 60, 71 to 72 and 93 to 104 months respectively). The effect of age at calving, season, year and parity on reproductive performance was significant (P<0.05). Reproductive performance decreased from parity ≥ 6. Reproductive performance during summer season was significantly lower than other seasons, specially compared to winter. The result of this study demonstrated that the reproductive performance decreased by increase in age at calving, parity and warm season.
