الفهرس 
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Abstract
مIn the late 1980’s breakthrough technology allowed scientists to discover the process of separating X and Y-bearing semen for the gender selection of embryos. By the mid-1990’s, this procedure was advanced enough to generate offspring of a desired sex. This development was called sexing semen.
The current work aimed at using sexed semen without or with administration of I/M GnRh for determination of fetal sex in dairy heifer, the study was performed on 300 heifers, that were divided into 3 groups. The first group was artificially inseminated by conventional semen; the second group was inseminated using sexed semen; while the third group was inseminated using sexed semen combined with GnRH injection at the time of insemination. Fertility indicators recorded were; gestation period, sex of offspring, percentage and incidence of dystocia, percentage of incidence post-partum diseases, fresh period, incidence of first postpartum estrus. Number of straw’s till conception after fresh period
from the present work, the following results were obtained:
1. The total conception rate after 3 inseminations was significantly higher (P<0.05) in conventional semen than sexed semen without GnRH (63% Vs 49%).
2. Whereas conception rate achieved by sexed semen with GnRH group (54%) was statistically equivalent to the conventional semen group.
3. The number of insemination per conception did not differ significantly among groups.
4. Both heifers that received sexed or conventional semen showed no difference in length of gestation (276 ± 4.39 - 275 ± 3.96 days) or weight of calves at birth (30.7 ± 2.38 - 32.0 ± 3.73 kg).
5. The percentage of female calves was higher in sexed semen without GnRH group (100%) and sexed semen with GnRH group (96.23%) than that recorded in conventional semen group (37.7%).
6. Incidence of dystocia/metritis/retained placenta did not differ significantly among all groups (P˃0.05).7. Two heifers were aborted in the conventional semen group while 1 heifer was aborted in each of the other groups, calving rate was 61% for conventional semen, 48% for sexed semen without GnRH, and 53% for sexed semen with GnRH group.
8. First lactation conception rate was not significantly different among groups.
9. Calving to -first estrus interval was non-significantly shorter in sexed semen with GnRH group recorded at 22.7 ± 7.76 days. Also no difference was observed among groups in either calving to -first insemination interval (55.7 ± 3.59-56.1 ± 3.95 days) or days open (71.5 ± 10.5-73.8 ± 7.69 days).
10. The number of insemination per conception was non-significantly lower in sexed semen with GnRH group recorded at 1.75 ± 0.44 straws. Type of semen did not affect daily milk yield or total milk yield at 305 day of heifers at their first lactation season
It could be concluded that administration of GnRH at time of insemination of sexed semen improved conception rate of virgin dairy heifers.