Pregnancy rates after ewes were treated with estradiol-17beta and oxytocin.

Authors: Lewis, Gregory

Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2010
Publication Date: 3/30/2010
Citation: Lewis, G.S. 2010. Pregnancy rates after ewes were treated with estradiol-17beta and oxytocin. Small Ruminant Research. 25:21-25.

Interpretive Summary: Surgical procedures have been used to successfully collect and transfer sheep embryos. The anatomy of the sheep cervix makes nonsurgical (i.e., transcervical) embryo collection and transfer exceedingly difficult and, to date, considerably less effective than surgical procedures. Even though some of the surgical embryo transfer procedures for sheep have been minimally invasive, they include the use of analgesics, anesthetics, incisions, and sutures. In addition, the number of people who are qualified to perform surgical embryo transfers has limited the use of the procedure worldwide, especially in countries such as the United States where the use of reproductive technologies for sheep is not widespread. Treatment of ewes with estradiol-17beta on day 6 and 400 USP units of oxytocin 10 hours later, on day 7, after the expected onset of estrus has been used to dilate the cervix and reduce the difficulty of manipulating a catheter through the cervix and into the uterus. Cervical dilation may improve transcervical sheep embryo transfer procedures, if the cervical dilation method does not reduce pregnancy rates. Thus, this experiment was conducted to determine whether treating ewes with estradiol-17beta and oxytocin on days 6 and 7, respectively, after the expected day of onset of estrus and mating would affect pregnancy rates on day 25. Neither estradiol-17beta, oxytocin, nor the combination of estradiol-17beta and oxytocin affected pregnancy rates on day 25. These results will be used to design additional studies to determine whether transcervical embryo transfer after estradiol-17beta-oxytocin treatment on days 6 and 7, respectively, will produce acceptable lambing rates.

Technical Abstract: Cervical dilation may improve transcervical sheep embryo-transfer procedures, if the cervical dilation method does not reduce pregnancy rates. This experiment was conducted to determine whether estradiol-17beta-oxytocin treatment, which dilates the cervix in luteal-phase ewes, affects pregnancy rates on day 25. The following treatments were assigned to ewes: 1) diluent + saline (n = 26); 2) diluent + oxytocin (n = 25); 3) estradiol-17beta + saline (n = 22); and 4) estradiol-17beta + oxytocin (n = 24). On day 6 after the expected onset of synchronized estrus and mating, ewes received either a 5-mL intravenous injection of diluent (i.e., 50% ethanol:50% sterile, isotonic saline) or an intravenous injection of 100 microgram of estradiol-17beta in 5 mL of diluent. At 10 h after the initial injections (i.e., morning of day 7), ewes received either a 20-mL intravenous injection of saline or a 20-mL intravenous injection containing 400 USP units of oxytocin. Intravenous injections were via a jugular vein. Jugular blood samples for progesterone assay were collected on days 6, 7, 8 (i.e., Period 1), 16, 18, 20, 22, and 25 (i.e., Period 2) after the expected onset of estrus and mating. Transrectal ultrasonography 25 days after the expected onset of estrus and progesterone concentrations were used to diagnose pregnancy. Because the ewes in this study were destined to be sold as culls, lambing data could not be collected. Neither estradiol-17beta nor oxytocin affected pregnancy rates, and the estradiol-17beta x oxytocin interaction was not significant. The pregnancy rate for diluent + saline was 61.5% (16/26); diluent + oxytocin, 76% (19/25); estradiol-17beta + saline, 77.2% (17/22); and estradiol-17beta + oxytocin, 62.5% (15/24). Progesterone concentration was greater (P < 0.05) in pregnant than in nonpregnant ewes (5.2 ± 0.3 vs. 2.0 ± 0.6 ng/mL). Over all ewes, day affected progesterone concentrations, and the pregnancy status x period interaction was significant (P < 0.01). For pregnant ewes, day and period affected (both P < 0.01) progesterone concentrations. For nonpregnant ewes, day affected (P < 0.01) progesterone concentrations, and the estradiol-17beta x oxytocin x period interaction was significant (P < 0.01). Treatment with estradiol-17beta on day 6 and oxytocin 10 h later, on day 7, after the expected onset of estrus to dilate the cervix and reduce the difficulty of transcervical embryo transfer should not induce luteolysis or disrupt pregnancy in ewes.