Technical note: development of a transcervical oocyte recovery procedure for sheep

An oocyte recovery procedure was developed and evaluated to determine whether a transcervical embryo recovery procedure is feasible with our method, which includes estradiol-17beta (E2) and oxytocin (OT) treatments, for dilating the cervix in ewes. On d 6 of an estrous cycle, oocytes were recovered either transcervically or with a laparotomy procedure. In the laparotomy group, ovulation rate was determined during the procedure and was used to calculate the percentage ofoocytes recovered. The laparotomy procedure was a standard uterine flush, and 12 mL of PBS was used to flush each uterine horn. In the transcervical group, the ovaries in each ewe were evaluated ultrasonically to determine ovulation rate. For transcervical recovery, 100 microg of E2 were injected i.v. on d 5 to increase cervical OT receptors, and 100 USP units of OT were injected i.v. 10 to 12 h later to dilate the cervix. Approximately 25 min after OT, ewes were placed in dorsal recumbency in a Commodore cradle, and a modified Foley catheter was passed through the cervix and into the uterus for injection (80 to 210 mL) and aspiration of PBS. The PBS was aspirated with a vacuum pump. The percentage of PBS recovered was greater (P<.01) at laparotomy than with the transcervical procedure (85.8 vs. 36.2%). Despite that difference, oocyte recovery did not differ significantly between the two groups (67% for laparotomy vs. 50% for transcervical; [oocytes recovered/number of corpora lutea] x 100), and there was no evidence that the transcervical procedure damaged the oocytes; the zona pellucida remained intact around all of the oocytes. In conclusion, a procedure that includes E2-OT-induced cervical dilation, passage of a modified Foley catheter into the uterus, and incremental infusion and aspiration of media through the catheter can be used to recover oocytes transcervically from ewes. This procedure may make transcervical embryo recovery feasible for sheep.