EXOGENOUS OXYTOCIN DILATES THE CERVIX IN EWES

Cervical anatomy in ewes usually prevents nonsurgical, intrauterine AI and transcervical embryo transfer (ET), which limits their commercial use in sheep. This study was conducted to determine whether oxytocin would dilate the cervix in ewes and permit passage of a stainless steel rod into the uterus. In Exp. 1, at 44 and 52 h after removal of progestogenated pessaries, ewes were injected i.v. with 0 (saline), 200, 400, or 600 USP units of oxytocin. Immediately before and after treatments, stainless steel rods were used to evaluate cervical dilation and determine whether the uterus could be entered. A rod could not be passed through the cervix and into the uterus in any of the saline-treated ewes. All doses of oxytocin given at 44 and 52 h after pessary removal dilated the cervix and permitted easy passage of a rod into the uterus. At both 44 and 52 h, a stainless steel rod was passed into the uterus in 33 of 43 (77%) of the oxytocin-treated ewes. In 93% (40/43) of these ewes, a rod could be passed into the uterus during either the 44-h or during the 52-h attempt. In Exp. 2, on d 9 after pessary removal, ewes were injected i.v. with oxytocin (400 USP units) at 6 or 12 h after i.v. estradiol-17-beta (0, 100, or 200-mu-g). Cervical dilation was evaluated as in Exp. 1. Dose of estradiol x time of oxytocin affected (P < .01) the proportion of ewes in which a rod could be passed transcervically into the uterus. A rod was passed into the uterus in 83% of the ewes treated with oxytocin 12 h after 100 and 200-mu-g of estradiol-17-beta; maximum success rate was 50% for the other treatments. Results indicate that oxytocin given 44 and 52 h after pessary removal and estrogen and oxytocin given 9 d after pessary removal dilated the cervix in ewes. These treatments may be useful for improving AI and ET procedures in sheep.