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The aim of the present study was to study the implementation of two different estrus synchronization protocols in dairy heifers and the application of artificial insemination with sex-determined sperm at a predetermined level under field conditions. For this purpose, heifers from two farms in the area of the Regional Unit of Thessaloniki (Farm A and Farm B) were used. In Farm A 10 Holstein dairy heifers aged 14-16 months and weighing 350-450 kg, while in Farm B 10 Holstein dairy heifers aged 14-6 months and weighing 350-450 kg were used. For the synchronization of the estrus of Farm A animals D-shaped intravaginal coils (2g ovarelin, PRID® Delta) were used. A combination of gonadotropic hormones and prostaglandin (ovarelin and cevaprost) to synchronize the estrus of Farm B animals was used. In group A heifers, 7 days after insertion the intravaginal coils were removed and 25 mg of prostaglandin PGF2α (5 ml / heifer) was administered. Artificial insemination was applied approximately 72 hours after removal of the coils. Group B heifers were given 2 ml of gonadorelin / heifer (Ovarelin, 50 mg gonadorelin / ml). On days 7 and 8, 5 ml of prostaglandin PGF2α / heifer (Cevaprost) was administered intramuscularly. On the 9th day 2 ml of gonadorelin / heifer (Ovarelin, 50 μg gonadorelin / ml) was administered again and finally on the 10th day artificial insemination was performed. Pregnancy diagnosis by ultrasound was performed 40 days after the artificial insemination. In Farm A the use of PRID DELTA intravaginal coils for the synchronization of oestrus and the application of artificial insemination at a specified time resulted in a 60% conception rate. In Farm B conception rate reached to 70%. In conclusion, our results showed that the application of gonadotropins and prostaglandin in dairy heifers in combination with the application of timed-artificial insemination with sex-sorted semen had satisfactory results.