Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/27/2000
Publication Date: 3/1/2001
Citation: Journal of Animal Science. 2001. v. 79. p. 568-573. Interpretive Summary: Artificial insemination (AI) in sheep is not widespread because the unusual anatomy of the cervix in ewes makes passage of a pipette into the uterus very difficult. A feasible transcervical AI method for sheep must include a method for coping with the anatomy of the cervix without inducing trauma. Injected oxytocin dilates the cervix and facilitates transcervical, intrauterine AI, but lambing rates have been variable and mostly low. This study was conducted to determine whether an oxytocin treatment could be used to assist transcervical passage of an AI instrument and to determine whether this affected the outcome of AI. Cervical manipulation, associated with transcervical AI in sheep does not seem to affect fertility after laparoscopic AI or lambing rates after the subsequent estrus in ewes that did not conceive to AI. However, injected oxytocin used to facilitate transcervical AI decreased lambing rate. Nevertheless, oxytocin-induced cervical dilation may aid in training of AI personnel. Because cervical manipulation alone does not seem to reduce lambing rates, transcervical AI in sheep still seems to be a promising procedure. Perhaps lower doses of oxytocin will still facilitate transcervical AI and not reduce fertility.
Technical Abstract: Difficulty of cervical penetration during transcervical artificial insemination (TAI), limits its use in sheep. Trauma of cervical manipulation (CM) may explain low fertility after TAI. We investigated effects of cervical dilation using exogenous oxytocin (OT) to facilitate TAI and its effect on reproduction after AI to a synchronized estrus. In Exp.1, we determined whether OT and(or)CM before laparoscopic AI (LAI) affected interval from pessary removal to ovulation and fertilization rate (FR). 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: 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 all ewes were bred by LAI 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 to detect ovulation time by ultrasonography. Treatments did not affect(P > 0.05) combined ovum/embryo recovery(69%), but OT-CM decreased FR(59 vs 47%;P < 0.05). OT tended to reduce interval to ovulation (OT, 62 h vs saline, 66 h; P < 0.06). For Exp. 2, 25 min before sham CM or CM, 200 USP units OT or 10 mL saline were injected i.v. and followed by LAI after sham CM or CM. At 10 to 12 d after AI, ewes were mated to Suffolk rams. Lambing rate was 62% in saline-sham ewes. CM did not affect lambing rate (64%). OT decreased (P < 0.05) lambing rate (56%) in OT-sham and in CM ewes (43%). Neither CM nor OT affected lambing to next estrus after AI. Oxytocin assisted TAI appears to warrant further investigation for sheep.