This study was conducted on data which collected from the filed Cattle in the college of Agriculture / University of Baghdad for the period from 1/7/2013 to 1/10/2013, which included 28 cows of Holstein Friesian to show the effect of sex of birth and the stage of lactation on Milk production and the main components. Our results showed The highest average milk production for female foster cows recorded in the first week with a value of 233L . The results show that had no significant effect of sex of birth on milk production and the main components. The results showed that the highest values of milk fat, lactose and minerals in the seventh week of lactation, which values were (3.559, 4.337and 0.638%) respectively, while the highest protein value was recorded in the third week (2.821%). There was no significant interaction among chemical components and stage of lactation , despite the superiority of the milk of female foster cows on the milk of male foster cows in some traits..