ABSTRACT 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 F 2α 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.
Bandai et al. (Thu,) studied this question.