Former researchers found that there are differences of shape, cap size, motility ability, age, electricity and chemical characters between Y and X chromosome bearing sperm. Y sperm moves f aster, has smaller size but shorter life time within f emale reproduction tract. In opposite, X sperm is 3% fatter and has more round shape. Concerning its bigger shape, X sperm moves slower, but has longer life time in f emale reproductive tract. Based on that matter, this research was conducted to find out the sex of born calves depend on insemination time, early to inseminate, best time to inseminate and late to insem.inate. This research used 40 head of cows, divided by four groups; each group consists of 10 head. Control group was inseminated by sexed semen, first, second, third and forth group was inseminated by unsexing semen, respectively on early, the best and late time of insemination. Successfully pregnancy was obtained from the best time insemination, both by sexing and unsexing semen. While born calves sex were not significant different, meant almost the same, from. both semen. Research result showed insemination by both sexing and unsexing semen which was done in early time to inseminate will tend yield female calve
