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 (CIDRR) 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 60 h 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 CIDRR treatment was significantly (P<0.05) earlier (mean: 24.9 h) than that in ewes treate with MAP sponge (mean: 30.0 h). 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 CIDRR-treated ewes. For control ewes, they were 59.1% and 1.62; and 47.6% and 1.90 for MAP and CIDRR treatments, respectively. There was no significant differences in the lambing rates and prolificacy between MAP and CIDRR 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 60 h) and CIDRR (48 h). A significant difference in the lambing rate was found among the sheep farms conducting the present study.