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 (CIDRR) 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 CIDRR (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 CIDRR-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 CIDRR during the non-breeding season.

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The mean ovulation rate of ewes treated during spring was significantly (P<0.01) lower than that of ewes treated during autumn (8.4 and 14.7, respectively), but there were no significant differences in the number of recovered ova and normal embryos between autumn and spring. Replacing the CIDR device on Day 9 of the 12-day insertion period maintained the P4 concentrations during gonadotropin treatment but did not improve ovulation rate, number of recovered ova and normal embryos of ewes treated in both autumn and spring. Developmental capacity of the early embryos (1 to 8 cell stage) to morulae or blastocysts did not significantly differ between autumn (45.7%) and spring (34.4%). These results indicate that the type (MAP sponge or CIDR device) and the number (one or two) of the progestogen devices did not affect ovulation rate, number of recovered ova or normal embryos, and a seasonal effect was found only in the ovulation rate but not in the number of recovered ova, normal embryos or the subsequent developmental capacity of cultured embryos.