A Comparative Analysis of Double-Ovsynch and Ovsynch-Heat-Synch Protocols on Pregnancy Rates in Primiparous Dairy Cows

Today, ovulation synchronization methods are widely used to improve fertility in dairy cows. In this regard, this research was conducted in one of the dairy herds in East Azerbaijan province, Iran. The cows were randomly divided into two groups. Ovsynch-Heat-Synch Group: This group included 30 primiparous cows. One month after calving, provided the uterus was clean, the synchronization program commenced. On the first and ninth days, they received GnRH, and on the seventh day, PGF2α intramuscularly. One week later, they received GnRH again; seven days after that, they received PGF2α, and 24 hours later, 1 mg of estradiol benzoate intramuscularly. Cows that showed estrus after the estradiol injection were inseminated using the AM/PM method, while those that did not show estrus 48 hours after the estradiol injection were artificially inseminated (Timed Artificial Insemination, TAI). Double-Ovsynch Group: This group also included 30 primiparous cows. One month after calving, provided the uterus was clean, the synchronization program began. On the first and ninth days, they received GnRH analogue; on day seven, PGF2α was administered intramuscularly. One week later, they received GnRH analogue again; seven days later, PGF2α was given, and 48 hours later, they received GnRH analogue intramuscularly. Forced insemination was performed 16 to 24 hours after the last GnRH injection. Pregnancy diagnosis was conducted using ultrasound between days 30 to 35 and by rectal palpation between days 40 to 45 after artificial insemination. The results showed that the fertility rate was 43.3% (13 cows) in the Ovsynch-Heat-Synch group and 60% (18 cows) in the Double-Ovsynch group. In the statistical analysis, this difference was not significant (p>0.05). This study indicated that the new Ovsynch-Heat-Synch method does not have a significant superiority over the Double-Ovsynch method.