Abstract:

This study was carried out to determine the efficacy of replacing the second Gonadotropin-Releasing Hormone (GnRH) with human Chorionic Gonadotropin (hCG) on pregnancy rate and plasma progesterone level in ovsynch protocol in cows. Thirty-six cows were randomly divided into two treatment groups: OV-GnRH (n=20) and OV-hCG (n=16) groups. All cows were treated with GnRH on day 0 and PGF2α on day 7. On day 9, cows in OV-GnRH group were injected with GnRH while those in OV-hCG group were injected with hCG. Pre-ovulatory follicle sizes (±S.E.M.) were examined by ultrasonography on 9 and 10 days. All cows were inseminated 16-18 h after the last injection. Ovulation and pregnancy examinations were performed by ultrasonography at 24 h and on 30 day after the insemination, respectively. Blood samples were collected on artificial insemination day and then at 5 and 12 days for progesterone assay. Mean pre-ovulatory follicle sizes on last injection and insemination days were determined 1.41±0.06 and 1.53±0.06 cm in OV- GnRH group, 1.56±0.08 and 1.67±0.06 cm in OV-hCG group. Ovulation and pregnancy rates were 90% and 40% for OV-GnRH group and 93.75% and 56.25% for OV-hCG group. Pre-ovulatory follicle sizes and ovulation and pregnancy rates did not differ significantly between groups (P>0.05). It is concluded that hCG can be used instead of the second GnRH injection in ovsynch protocol in cows according to the results obtained from this study.

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