Effect of active immunization against ovine inhibin alpha subunit on ovarian activity, and application of inhibin immunization to superovulation and twinning in Japanese black cows

Summary : Inhibin immunization increases the ovulation rate in cows. In this study we investigated the effect of active immunization of Japanese Black cows against the recombinant ovine inhibin a subunit on ovarian activity. In addition we examined whether inhibin immunization could be applied to superovulation and twinning in Japanese Black cows. Cows (n=8) were injected with 2ml of inhibin vaccine as primary injection at estrous day, followed by a booster injection (2ml) 4 weeks later. The control cows (n=5) received adjuvant only. Ovaries were examined by rectal palpation and using ultrasonography during 2 to 5 months after primary. Superovulation and twinning were attempted on 2 and 4 of 23 estrous cycles in immunized cows, respectively. The cows were run with artificial insemination at the day of estrus for both trials, and embryos were recovered for superovulation at 8 days after artificial insemination. The number of estrous follicles (10mm =<) and corpora lutea (7.0=+- 1.9, 3.1=+-1.2, 23 cycles) of the immunized cows were higher than those of control cows (1.1=+-2.2, 1.1=+-1.4, 16 cycles). Multiple follicular development and ovulation were observed during successive estrous cycles in the immunized cows. In the superovulation trial, nine and 4 transferable embryos were recovered from each cow. The transferred embryos resulted in the birth of three calves. One of 4 cows of the twinning trial gave birth to twin calves. In conclusion, active immunization against the recombinant ovine inhibin a subunit induces successive multiple development of estrous follicles and multiple ovulation in Japanese Black cows. These experiments also show that inhibin immunization can be applied for superovulation in Japanese Black cows. In addition one twinning was induced in immunized cows. The present study is the first reported application of inhibin immunization resulting in successful superovulation in domestic animals.