ヒツジインヒビンαサブユニットの能動免疫が黒毛和種牛の卵巣機能に及ぼす影響とその過排卵誘起処置および双子生産への適応性

インヒビン免疫はウシで排卵率を高めることが知られている。本研究では,組換え体ヒツジインヒビンαサブユニットを抗原とした黒毛和種牛への免疫が卵巣反応に及ぼす影響を検討した。また,過排卵誘起処置ならびに双子生産へのインヒビン免疫の適応性を調べた。免疫区として黒毛和種雌牛8頭に初回免疫時にインヒビンワクチン2mlを投与し,28日後に追加免疫として同量を投与した。対照区の5頭にはアジュバントのみを投与した。免疫後2-5ケ月の間,卵巣の変化を直腸検査ならびに超音波画像により追跡した。免疫区で観察した23発情周期中2および4発情周期について,それぞれ過排卵誘起処置ならびに双子生産を試みた。それぞれの試験に用いた供試牛は,発情日に人工授精を行い,過排卵誘起処置ではさらに人工授精後8日目に胚回収を行った。免疫区(23発情周期)では,発情卵胞(10mm≦)および黄体数は7.0±1.9,3.1±1.2であり,対照区(16発情周期)の1.1±2.2,1.1±1.4より多かった。免疫区では連続した発情周期で複数の卵胞発育および排卵が観察された。過排卵誘起処置では,2頭からそれぞれ4および9個の移植可能胚が得られ,胚移植の結果,3頭の産子が得られた。双子生産では4頭中1頭で双子が生産された。以上のことから,黒毛和種牛において組換え体ヒツジインヒビンαサブユニットの免疫は,連続した発情周期で複数の発情卵胞の発育ならびに複数排卵を誘発し,さらに過排卵誘起処置ならびに双子生産への応用が可能であることが明らかになった。なお,本研究は,性腺刺激ホルモンを併用しないインヒビン免疫のみによる過排卵誘起処置の成功例として,家畜における初の報告例である。

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 α 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 α 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.

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