The environmental factors on the lamb growth, analytically studied with extra-seasonal-lambs II : Extra-seasonal-lamb-production by the combined treatment

季節外生産羊を利用しためん羊発育に及ぼす環境要因の分析的研究II : 単日処理とホルモン処理併用法による子羊の季節外生産

Mimura Ko

Asahida Yasushi

Morita Haruka

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

　第1報において筆者らは，非繁殖期のコリデーノレ種雌羊を短日処理すると，長日から短日に変化してからほぼ40~50 日で人工的に発育を誘起できること，しかし第1回の発情では多くの場合妊娠しないこと，しばしば弱い子羊を生産することなどを報告した.
　短日処理によるめん羊の人工発情誘起法は，長期間を要する，管理に手数を要するなどの問題を有するが，反面最近数多く報告されているホノレモン処理法では，高価な薬品を相当量使用する他，その効果が比較的確実でない欠点が指摘される.
　筆者らは，両方法の併用法，すなわち強度の短日処理1週間(以後ホルモン処理終了まで同一日照時間維持)―黄体ホノレモン25mg/ 日x3~5 筋注-2 日後P.M.S. 750 i. u 筋注法の効果を試験した.またこの場合短日処理は，厚い黒頭巾を雌羊の頭に被せ，明るい羊舎内に放置する簡便法によった.
　1959~1961 ，6回に亘り21 頭を試験したが，発情と認められたもの19 頭(90%) ，妊娠―分娩，卵巣所見―黄体・グラーフ卵胞の存在により確実に発情と認められたものは17 頭， 81%に達した.また第6回試験では併用法による4頭をホルモン処理法による3頭と比較したところ，確実に発情したもの前者100% に対し，後者は33%であった.
　黄体ホルモン処理日数を3日に短縮しでも5日間の処理となんら差異を認めなかった.
　強度の短日処理により，下垂体機能の亢進乃至反応閥値の低下など，本併用法による人工発情誘起のメカニズムについても論議した.
　なお処理羊はP.M.S. 筋注後2日目に最も多く発情し， GORDON (1958) の報告と一致した.

Following decreasing daylight treatment for 7 days, twenty four anoestrous ewes of Japanese Corriedale were injected with P.M.S. 750 i. u. after 3-5 injections of progesterone 25mg daily. The ewes in pretreatment of light were hooded with black thick-cloth, and were under control hours of daylight.

This combined treatment was studied over three years 1959-1961, and the incidence of oestrus, presence of corpora lutea, and the state of follicular development was studied.

Total 13 lambs were produced by nine of twenty-one ewes treated with the method, and average percentage of lamb-production per ewe was 1.44.

The presence of corpora lutea and Graafian follicle was observed cytologically in 8 of I 0 ewes when their ovaries were examined at slaughter time. Seventeen of twenty-one ewes were induced oestrus and the percentage is about 81%.

In the sixth trial, three ewes were under progesterone-P.M.S. treatment alone, and only one cytologically was observed in fertile. The percentage is 33%. Therefore, the hypothesis may be probably explained that the light treatment prior to hormone administration will reduce the threshold in pituitary activity to induce the ovarian activity to much lower level.

There is no difference between the method of three days injection daily and the method of five days injection. Thus the method combined the pretreatment of decreasing daylight by a black hood with progesterone 25mg x 3 and P.M.S. 750 i. u. may be considered of practical application.

The highest response was observed two days after the time of P.M.S. injection, followed by next day, and this is agreed with GoRDON's result.

Animal husbandry [ 640 ]

eng

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563