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The study was conducted on 21 cows of Holstein - Friesian, presented in the farm of Coll. Vet. Med. University of Baghdad. The age of the animals ranged between 6 to 8 years and the numbers of parturition were 3-6. The cows were divided into groups according to the milk production in the season. The 1st group consist of 11 cows which produced 200-300kg/ season. While the 2nd group consist of 10 cows, which produced 300-400 kg/ season. The animals were also divided according to the numbers of parturition, cows with 3-4 birth (10), and cows with 5-6 birth (11). The sex of the calf were also taken in consideration. The results showed that there was no significant difference in milk production affecting open days and in the numbers of parturition that affect days open. The sex of the calf showed a significant difference (P? 0.05) on the open days. The cows that give birth female calf having more open days as compared with those give male calf. It was concluded from this study that milk production and parity have no effect on days open, while the sex of the calf especially female calf have a significant difference on days open .