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

The difficulty of cervical penetration severely limits the use of transcerv ical AI (TAI) in sheep, and trauma from cervical manipulation (CM) may redu ce fertility after TAI. We investigated the effects of cervical dilation us ing exogenous oxytocin (OT) to facilitate TAI and its effects on reproducti ve variables after laparoscopic AI (LAI). Estrus was synchronized by insert ing pessaries impregnated with 6 alpha -methyl-17 alpha -hydroxyprogesteron e acetate (60 mg) for 12 d. In Exp. 1, we determined whether OT and CM befo re LAI affected the interval from pessary removal to ovulation and fertiliz ation rate. Crossbred ewes (n = 16) were assigned to 1) saline-CM or 2) OT- CM. In Exp. 2, effects of OT and GM on lambing rates were evaluated with wh ite-faced ewes (n = 220) in a 2 x 2 factorial experiment: I) 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 late r. In Exp. I, ewes received i.v. either 400 USP units of OT or 20 mL of sal ine at 30 to 60 min before LAI, and CM was administered as for TAI. Beginni ng 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 C M interaction in Exp. 1 was not significant. For Exp. 2, approximately 25 m in before sham CM or CM, 200 USP units of OT or 10 mL of saline was injecte d 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 treatm ent 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 C M nor OT before LAI affected lambing rates to next estrus, indicating no lo ng-term damage to the cervix or uterus. In summary, CM did not affect ferti lity after LAI, but OT decreased lambing rate independent of CM. If OT will not be usable for TAT, it may still be a tool for training TAI personnel.