RECENT ADVANCES IN CRYOPRESERVATION OF SEMEN AND ARTIFICIAL INSEMINATIONIN SHEEP: A REVIEW

摘要

Cryopreservation of semen facilitates widespread dissemination of superior germplasm and thus allowing the full exploitation of artificial insemination (Al) benefits. Recent focus is on preserving fertilizing capacity of frozen spermatozoa by improving the composition of extenders and changing cooling/freezing protocols, use of cryoprotectants, antioxidants, including enzymes, vitamins, amino acids and proteins, plant extracts and other compounds. In addition, research is also intensified on role ofseminal plasma and its proteins as well as cholesterol-loaded cyclodextrin in semen freezing. Recently it has also been shown that helium-neon laser irradiation of cryopreserved ram sperm increased the post-thaw sperm motility, viability, cytochrome c oxidase activity and ATP contents with no significant changes in DNA and acrosome integrity. Post-thaw sperm motility of cryopreserved semen ranged from 33.3 to 72.2%. Fertility depends on the insemination technique and ranged from 45 to 80% for laparoscopic and 4 to 42% for transcervical insemination. Further, the complex anatomy of ewe's cervix is also a hurdle affecting intrauterine deposition of semen and consequently the fertility of frozen-thawed semen. Researchers are attempting cervical dilation with the use of hormones and chemicals to facilitate catheter penetration in the cervical canal. This review gives a detailed semen processing techniques and their effects on semen quality and Al techniques used in sheep and their success rates.