부산대학교 도서관

Background: Artificial insemination (AI) can serve as a powerful tool to the sheep owners for making rapid geneticprogress of their flock. The AI in sheep is mostly performed using fresh semen with two reasons i) lambing ratefollowing trans-cervical AI with frozen semen is limited by the inability of frozen-thawed sperm to transit the cervixand ii) the need of circumventing the cervical barrier through laparoscope aided intrauterine AI. Therefore, AI withfrozen-thawed semen is not as widespread in sheep as it is in other domestic species. However, to get maximumbenefits through the use of AI, frozen-thawed semen is a prerequisite because instead of high fertility, the shortshelf life of fresh semen coupled with a limitation on the number of insemination doses achievable per unittime restricts the widespread use of individual sires. Therefore, in order to enhance lambing rate, a total of 240trans-cervical artificial inseminations with frozen-thawed semen were performed in Bharat Merino ewes duringautumn season either once in the evening (G-I, 10 h after onset of estrus, n = 100) or twice (G-II, 14 h and 22 hafter onset of estrus, n = 140) i.e. once in the morning and again in the evening. Results: The pregnancy rate (proportion of pregnant ewes confirmed by ultrasonography at day 40) and lambingrate (proportion of ewes lambed) were higher in G-II as compared to G-I (26.4 vs 20% and 19.3 vs 10%, respectively). The difference in lambing rates was statistically (P < 0.05) significant. The depth of insemination within cervico-uterinetract had no significant effect on pregnancy and lambing rates. Conclusions: The results indicate that lambing rate in sheep following TCAI with frozen-thawed semen wassignificantly influenced by time of inseminations. Two inseminations after 14 and 22 h of onset of estrusenhanced the lambing rates of Bharat Merino sheep as compare to single insemination after 10 h of onset ofestrus. The TCAI technique with frozen-thawed ram semen is promising and may serve as a valuable tool forgenetic improvement of sheep breeds. Research efforts are going on worldwide to overcome the poor fertilityfollowing TCAI with frozen-thawed semen.