Lambing Rates by Fixed-Time Intrauterine Insemination with Frozen Semen in Seasonally Anestrous Ewes Treated with a Progestogen-Impregnated Sponge or CIDR Device.

Abstract

During the non-breeding season (April to July), 187 ewes treated wth either an intravaginal sponge impregnated with medroxyprogesterone acetate (MAP) or a controlled internal drug release (CIDR®) device for 9 days and an injection of pregnant mare serum gonadotropin (PMSG) at one day before the cessation of progestogen treatment were inseminated into the uterus by laparoscopy with frozen-thawed semen at fixed-time basis (36, 48 or 60h after the removal of sponge or device). Insemination was also performed at 18 h after estrus detection as a control. The time to the onset of estrus after CIDR® treatment was significantly (P<0.05) earlier (mean: 24.9h) than that in ewes treated with MAP sponge (mean: 30.0h). The percentages of ewes lambing and lambs born per ewe lambing for inseminations at 36, 48 and 60 h were 66.7% and 1.69; 52.0% and 1.31; 46.2% and 1.75 for MAP-treated ewes, and 33.3% and 1.50; 73.9% and 1.53; 40.9% and 1.56 for CIDR®-treated ewes. For control ewes, they were 59.1% and 1.62; and 47.6% and 1.90 for MAP and CIDR® treatments, respectively. There was no significant differences in the lambing rates and prolificacy between MAP and CIDR® treatments and among the insemination times. An optimum time for an intrauterine insemination with frozen-thawed semen appears to be different in the use of MAP sponge (range: 36 to 60h) and CIDR® (48h). A significant difference in the lambing rate was found among the sheep farms conducting the present study.