抄録
精巣上体精子を凍結保存することは,稀少動物を始めとする種の生殖子を残す技術として重要である。犬の精巣上体尾部から回収した精子の凍結保存を行い,その精液を使用して受精能を検討した。その結果,実験犬17頭における精巣上体尾部の精液性状は,精子活力は平均89.4±1.6(SE)%,精子生存率は89.1±1.1%で,頭体部に比較して明らかに高値を示した(P<0.01,P<0.05)。回収精子数は6.3〜122.3×10^7と個体で幅が見られ,平均61.5±10.0×10^7であった。凍結保存には,精巣上体尾部から回収された精子だけを使用した。その凍結融解後の精子活力は19.5±2.3%,精子生存率は53.1±3.3%であった。これは,射出精子の凍結融解後のものと比較すると,若干低かったが両者の間には有意差は見られなかった。精子数2,3,4億を片側子宮内に授精した結果,3億を注入した1頭のみの妊娠であった(1/16,6.3%)。また,精子数1億を両側卵管内にそれぞれ授精した結果,6頭中1頭(16.7%)の妊娠であった。このようにビーグル犬の凍結した精巣上体精子は,融解後の性状は射出精子とほぼ同様であったにも関わらず,受胎率は低率であることが明らかとなった。今後はこれら両者の凍結融解後のダメージの違いを検討するとともに,受胎率を向上させる方法の開発が必要であると思われる。
Freeze-storage of epididymal sperm is an important technique for the preservation of gametes in animals, including those becoming extinct. We froze canine sperm recovered from the cauda epididymis and investigated the fertility. The qualities of sperm from the cauda epididymis before freezing were: mean sperm motility, 89.4±1.6 (SE)%; sperm viability, 89.1±1.1%; and these were significantly higher than those of sperm from the caput-corpus epididymis (P<0.0l, P<0.05). The number of sperm recovered from both cauda epididymides varied among animals: 6.3-122.3×l0^7, mean 61.5±10.0×l0^7. Freezing was used only for sperm recovered from the cauda epididymis. The sperm motility and viability after thawing were 19.5±2.5% and 53.1±3.3%, respectively. These were slightly lower than those of frozen-thawed ejaculated sperm, but the differences were not significant. When 2×10^8, 3×10^8, or 4×10^8 sperm were inseminated in the unilateral uterus, only one animal inseminated with 3 x 10^8 sperm was fertilized (1/16, 6.3%). When 1×10^8 sperm were inseminated in the bilateral uterine tubes, one of six animals (16.7%) was fertilized. Therefore, although the qualities of epididymal sperm after thawing were similar to those of ejaculated sperm, the conception rate obtained with frozen-thawed epididymal sperm was low in beagle dogs. It is necessary to investigate the differences in damage between epididymal sperm after thawing and ejaculated sperm and to develop a method for improving the conception rate.
