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

Abstract

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.

Traversing the ovine cervix – a challenge for cryopreserved semen and creative science

“…Although they found no detrimental effect of oxytocin on fertilisation rate, the transcervical technique per se appeared to reduce fertilisation rate. In contrast, Stellflug et al (2001) found no adverse effect of experimental cervical manipulation on fertility in laparoscopically inseminated ewes, but lambing rates were decreased by oxytocin-induced cervical dilation. Using a brass bulb tip to decrease cervical trauma and to guide the inseminating pipette, WulsterRadcliffe and Lewis (2002) found no adverse effect of transcervical insemination on fertility.…”

“…Such a conclusion is in keeping with the adverse effect on conception noted by King et al (2004) following systemic oxytocin administration before cervical insemination using frozen-thawed semen and the absence of a deleterious effect of the oxytocin on conception when the cervix was by-passed by laparoscopic intrauterine insemination. It is also in keeping with the data of Stellflug et al (2001), which imply that a combination of exogenous oxytocin and cervical manipulation accentuates the oxytocinmediated impairment of fertility following cervical insemination. Thus, King et al (2004) suggested that, when using oxytocin for enhancing cervical dilation and os cervix activity, it may be advantageous to replace a single relatively large bolus dose of oxytocin, which results in an extended period of elevated oxytocin concentrations, with a series of smaller doses that more closely mimic, in number, amplitude and duration, the pulses in plasma concentrations that occur during natural oestrus (Sheldrick and Flint, 1981;Wathes et al, 1986;Gilbert et al, 1991).…”

Plasma levels of cortisol and oxytocin, and uterine activity after cervical artificial insemination in the ewe

“…Therefore, it is tempting to speculate that a secretion of OT altering the contractile rate of the uterus for a long period is detrimental to fertility in a number of species, including the ewe. For example, it has recently been shown that the administration of OT at the time of AI does not improve pregnancy rates, and tends to reduce fertility [36,40,45]. Furthermore, there is evidence that in an attempt to enhance sperm transport, such an OT treatment in the ewe considerably diminishes the number of spermatozoa recovered in the fallopian tubes after insemination [27].…”

Mechanical and Pharmacologic Applications of Artificial Insemination in Ewes

“…Sayre and Lewis (1997) observed no undesirable effect of oxytocin on ovum fertilisation rate. Stellflug et al, (2001) show a negative effect of oxytocin but not of the transcervical insemination procedure. Fertilization rate decreases in the treatment of oxytocin-cervical manipulations.…”

“…The cervical manipulation seems to unfavorable an effect on fertility after AI, because the oxytocin treatment is not harmful. It likely to affect the sperm survival in the reproductive tract of sheep, or some issues of sperm capacitation (Stellflug et al, 2001). Perhaps, manipulation of the cervix may affect sperm transport within the reproductive tract, or a stressed cervix may produce a spermicidal compound (Hawk et al, 1981).…”