Oxytocin-induced cervical dilation and cervical manipulation in sheep: effects on laparoscopic artificial insemination

The difficulty of cervical penetration severely limits the use of transcervical AI (TAI) in sheep, and trauma from cervical manipulation (CM) may reduce fertility after TAI. We investigated the effects of cervical dilation using exogenous oxytocin (OT) to facilitate TAI and its effects on reproductive variables after laparoscopic AI (LAI). Estrus was synchronized by inserting pessaries impregnated with 6alpha-methyl-17alpha-hydroxyprogesterone acetate (60 mg) for 12 d. In Exp. 1, we determined whether OT and CM before LAI affected the interval from pessary removal to ovulation and fertilization rate. Crossbred ewes (n = 16) were assigned to 1) saline-CM or 2) OT-CM. In Exp. 2, effects of OT and CM on lambing rates were evaluated with white-faced ewes (n = 220) in a 2 x 2 factorial experiment: 1) saline-sham CM; 2) saline-CM; 3) OT-sham CM; and 4) OT-CM. In both studies, eCG (400 IU i.m.) was injected at pessary removal, and LAI was performed 48 to 52 h later. In Exp. 1, ewes received i.v. either 400 USP units of OT or 20 mL of saline at 30 to 60 min before LAI, and CM was administered as for TAI. Beginning 32 h after pessary removal and continuing at 8-h intervals, ovaries were examined with ultrasonography to estimate time of ovulation. Treatment in Exp. 1 did not affect combined ovum/embryo recovery rate (69%), but OT-CM decreased fertilization rate (47 vs 59%; P < 0.05). The OT tended to reduce the interval to ovulation (OT, 59 h vs saline, 66 h; P < 0.06). The OT x CM interaction in Exp. 1 was not significant. For Exp. 2, approximately 25 min before sham CM or CM, 200 USP units of OT or 10 mL of saline was injected i.v. The LAI was performed immediately after sham CM or CM. At 10 to 12 d after AI in Exp. 2, ewes were mated with Suffolk rams. Blood was collected between 24 and 26 d after AI for pregnancy-specific protein B (PSPB) RIA. The PSPB pregnancy and lambing rates were both 62% in saline-sham controls. The CM did not affect pregnancy (69%) or lambing rate (64%). The OT treatment decreased (P < 0.05) PSPB pregnancy (59%) and lambing rates (56%) in OT-sham ewes and pregnancy and lambing rates in CM ewes (both 43%). Neither CM nor OT before LAI affected lambing rates to next estrus, indicating no long-term damage to the cervix or uterus. In summary, CM did not affect fertility after LAI, but OT decreased lambing rate independent of CM. If OT will not be usable for TAI, it may still be a tool for training TAI personnel.