236 SUPEROVULATION IN SHEEP WITH REDUCED INJECTION FSH/eCG PROTOCOLS FOLLOWED BY TRANSFER OF FRESH OR VITRIFIED EMBRYOS

Abstract

The aim of this experiment was to compare a single FSH/eCG, or double FSH-0.5% hyaluronan/eCG injection protocol with a multiple FSH/eCG injection protocol on the superovulatory response and embryo production in sheep. In addition, the effect of vitrification of these embryos on the pregnancy rate following embryo transfer was evaluated. Eighty Dohne Merino ewes received an 8-day CIDR-S device (0.33 g P4; Zoetis, Florham Park, NJ, USA) plus 10 mg of FSH i.m. (Folltropin-V; Vetoquinol, Lavaltrie, QC, Canada) and 400 IU of eCG i.m. (Pregnecol; Vetoquinol) in 3 treatment groups. Group 1 (n = 21) received a single 10-mg FSH injection in saline and 400 IU of eCG in saline 2.5 days before CIDR withdrawal. Group 2 (n = 23) received 6.7 mg of FSH in hyaluronan (MAP-5, 50 mg; Vetoquinol) and 400 IU of eCG in saline 2.5 days before CIDR withdrawal and 3.3 mg of FSH in hyaluronan 0.5 days before CIDR withdrawal. Group 3 (n = 36) received 7 injections (am, pm) of FSH in saline (2.5, 2.0, 1.5, 1.5, 1.0, 1.0, 0.5 mg) starting 2.5 days before CIDR withdrawal and 400 IU of eCG in saline at the first injection. Ewes were inseminated with semen collected from 1 of 5 rams at 36 to 40 h after CIDR withdrawal. Donor ewes were slaughtered 6 days after AI (Day 0), CL were counted and ova/embryos were collected. Viable embryos were transferred in singles into Day 6 synchronised recipients as either fresh (n = 128) or following vitrification/thawing using the CVM (CryoLogic, Blackburn, VIC, Australia; n = 97; Fry et al. 2005 Reprod. Fertil. Dev. 17, 243). Pregnancy was diagnosed by ultrasound scanning on Day 45. Data for CL and transferable embryo were analysed by the Kruskall-Wallis test and differences between groups determined by the Dunn test. Data for pregnancy rates was compared by chi-squared analysis. The mean number of CL in Groups 2 and 3 were both significantly higher than that in Group 1 (12.3 and 12.0 v. 8.5; P < 0.05). Similarly, the total number of embryos/ova recovered in Groups 2 and 3 were significantly higher than for Group 1 (8.3 and 7.0 v. 5.0; P < 0.05). Group 3 produced more viable embryos than either Group 2 or Group 1 (4.6 v. 2.7 and 2.1; P < 0.05); however, data were skewed by the extensive use of semen from one ram in Group 2 that had a low fertilization rate (28%). The transfer of vitrified/thawed embryos resulted a nonsignificant (P > 0.05) 10% decrease in pregnancy rate compared with fresh embryos (66% v. 76%). In conclusion, the administration of the sustained release FSH-MAP-5 in a 2-injection protocol in sheep was as effective as a multiple FSH injection protocol in inducing an ovarian response but more research is required to elucidate the effect of FSH-MAP-5 on embryo quality. The successful vitrification of sheep embryos provides a promising technique for the storage and transport of embryos in large-scale sheep embryo transfer programs.