212 EFFECT OF OVULATION STATUS ON PREGNANCY RATES IN RECIPIENT GILTS TRANSFERRED WITH CLONED EMBRYO TRANSFER

Abstract

This study was conducted to determine the optimal stage of the estrus cycle to achieve the highest pregnancy rates in surrogate recipient gilts receiving somatic cell nuclear transfer (SCNT) embryos. Potential surrogate gilts over 7 months of age were checked at Day 21 of their estrus cycle for their estrous status by observing external signs: vaginal fluid, vulva redness, vulva swelling, and standing response to back pressure. Viscosity of vaginal fluid was evaluated and classified as none, medium, and strong. Vulva redness and swelling were respectively assessed as none or shrink, medium, and strong. Back pressure was estimated by an immediate move, standing less than 10 s, and standing over 10 s. Ovulation status was observed when surrogates had SCNT embryos transferred into their oviducts, and then ovulation status of each surrogate was classified depending on the follicular diameter, as follows: preovulation (PO – 17 surrogates; follicular diameter of PO was 3 to 5 mm), just prior to ovulation (JPO – 20 surrogates; follicular diameter of JPO was 6 to 8 mm), ovulating (IO – 12 surrogates; ovulation mark with JPO follicles), just after ovulation (JAO – 14 surrogates; ovulation mark without follicles), and after ovulation (AO – 24 surrogates; ovaries showed only corpora lutea). Real-time ultrasonograpy was used for pregnancy diagnosis by observing amniotic vesicles. All data were subjected to analysis of variance (ANOVA) and protected least significant difference (LSD) test using general linear models in a statistical analysis system (SAS Institute, Inc., Cary, NC, USA) program to determine differences among experimental groups. The first pregnancy diagnosis was done on Day 30 after ET and then repeated in 2-week intervals until Day 114. SCNT embryos transferred into JPO surrogates gave better pregnancy rates (9/20, 45%) than others (4% to 11%) on Day 30 after ET (P < 0.05). These results suggest that ovulation status of surrogate gilts is an important critical factor for pregnancy. This information indicates that surrogate gilts implanted with SCNT pig embryos just prior to ovulation can achieve optimal pregnancy rates. In conclusion, the JPO surrogate selected should strongly show all parameters (vaginal fluid, vulva redness, vulva swelling, and standing response to back pressure) for the preparation of surrogates.

This study was supported by the bio-organ production research grant (No.06020602) of the NLRI.