Fertility of Estrus-Induced Ewes during the Non-Breeding Season and Artificially Inseminated with Frozen Semen Imported from New Zealand

The present study was conducted to investigate fertility of estrus-induced ewes during the non-breeding season, artificially inseminated with frozen semen imported from New Zealand. A total of 122 Suffolk and Suffolk-crossed ewes in three different sheep farms (T, S, M) were treated with an intravaginal progesterone release device (CIDR-G) for 12 days, and an intramuscular injection of 500 IU equine chorionic gonadotropin one day before CIDR removal. Effects of intrauterine insemination doses (0.2 and 0.4 ml per head) and two rams on fertility were compared at Farm T using 75 ewes. At the other two farms (S and M), 0.1 to 0.2 ml doses were inseminated into the uteri on the fixed-time basis. The lambing rates of ewes inseminated with 0.2 and 0.4 ml doses were 68.4 and 59.5%, and the lambing rates of ewes inseminated with the two rams were 61.3 and 65.9%. No significant differences were found between any of the factors. The lambing rates on Farms S and M were 54.2% and 47.8%, respectively. Overall, there was no significant difference in the lambing rates (58.3% and 59.5%) and prolificacy (2.03 and 1.61) between the two rams. These results indicate that the fertility of ewes inseminated during the non-breeding season with frozen-thawed semen imported from New Zealand is acceptable and that new blood lines of Suffolk sires and dams can be produced on Japanese sheep farms.