Effect of Extended Duration of Progesterone-Based Ovulation Synchronization Protocol on Fertility in Japanese Black Cows.

We compared conception rates among Japanese Black cows undergoing ovulation synchronization protocols using intravaginal progesterone-releasing devices (CIDR) across three different treatment durations. Cows received CIDR treatment for 7 days in the Ovsynch (OS) group (n = 40), 8-10 days in the short-extended (SE) group (n = 42), and 11-14 days in the long-extended (LE) group (n = 67). Gonadotropin-releasing hormone (GnRH) was injected concurrently with the CIDR insertion. On the day of CIDR withdrawal (Day 0), all cows received a prostaglandin F2α injection. When estrus signs were visually observed from Days 0 to 2, artificial insemination (AI) was performed concurrent with the GnRH injection. Cows without any estrus signs received GnRH injection on Day 2, followed by timed AI 16-20 h later. Data from 149 AIs performed on 144 cows were analyzed. The LE group tended to show a higher estrus expression rate than the OS group (13.4% vs. 0.0%, respectively). Pregnancy per AI was comparable among all three groups (OS: 47.5%, SE: 47.6%, LE: 50.7%). In conclusion, extending the CIDR treatment duration did not affect the conception rates of Japanese Black cows. In LE group cows, AI following estrus detection is recommended to enhance pregnancy outcomes.