The effect of GnRH and hCG applications on pregnancy rate in postpartum dairy cows

The study was carried out to determine the effect of of GnRH alone at the time of artificial insemination and GnRH at the time of artificial insemination and the combined use of hCG on the 5th day after insemination in postpartum dairy cows on pregnancy rates. The study was conducted on 120 Holstein cows which were aging between 3-6 years old, the cows were on 70-120 days postpartum and had no reproductive problems. No hormonal application was carried out for ensuring estrus in cows. The ovarian examinations in cows showing signs of estrus during the study were performed rectally with 6–8 MHz linear probe real-time ultrasound (Falco, Pie Medical, Netherlands). The animals were randomly equal assigned into three groups. A GnRH analogue, Receptal® (0.004 mg Buserelin/ml, Intervet) containing buserelin acetate was administered at the time of insemination at a dose of 10 µg to Group I (n=40) intramuscularly. Group II (n=40) was administered 10 μg buserelin acetate intramuscularly at the time of insemination and 1500 IU hCG (Pregnyl® 3x1500 IU, MSD) intramuscularly on the 5th day after insemination. Group III was assumed as the control group and no administration was made during or after insemination. The pregnancy diagnosis was carried out on 30th days after insemination by transrectal ultrasonography Pregnancy rates were determined as 80% (32/40), 80% (32/40), 57.5% (23/40) in Groups I, II and III, respectively. Statistical difference was found between treatment groups and the control group in terms of pregnancy rates. As a result, it was found that the use of GnRH alone at the time of artificial insemination and combined use of GnRH at the time of artificial insemination and hCG on the 5th day after artificial insemination increase the pregnancy rates in postpartum dairy cows. However, it was concluded that hCG administration on the 5th day did not increase pregnancy rates compared to GnRH administration alone, therefore additional hCG administration was not necessary.