Insemination Doses of Frozen-Thawed Semen in Seasonally Anestrous Ewes Treated with Two Different Progesterone-Impregnated Intravaginal Devices

Abstract

During the non-breeding season, a total of 176 Suffolk ewes at 3 sheep farms were treated with either a self-made, progesterone-impregnated intravaginal sponge (P sponge) or controlled internal drug release (CIDR) for 9 days and an intramuscular injection of pregnant mare's serum gonadotropin (PMSG) 1 day before the cessation of progesterone treatment. At 44-52 h after treatment, 174 ewes were inseminated with 0.2, 0.1 or 0.05 ml of frozen-thawed ram semen per uterine horn with the aid of a laparoscope. There was no significant difference in lambing rate between P sponge (54.2%) and CIDR (61.5%). The insemination dose did not also affect the lambing rates in both P sponge-treated (51.7, 66.7 and 44.4% for 0.2, 0.1 and 0.05 ml, respectively) and CIDR-treated (58.1, 59.4 and 67.9%, respectively) ewes. Prolificacy was not significantly different between progesterone treatments nor among insemination doses. Lambing rates and prolificacy at the 3 sheep farms were not also significantly different. These results indicate that even a low insemination dose (0.05 ml) can result in similar rates of lambing compared with 0.1 or 0.2 ml of insemination dose per uterus in Suffolk ewes treated with either P sponge or CIDR during the non-breeding season. © 1993, THE SOCIETY FOR REPRODUCTION AND DEVELOPMENT. All rights reserved.