EMBRYO TRANSFER IN SHEEP AND GOATS

In response to the physiological demands governing the feasibility of embryo transfer (ET) in small ruminants, the techniques involved are constantly improving, as we intend to show in the following selective review. Whatever the aim, ET is dependent on sufficient yields of viable embryos from donors. The first Step in ET, superovulation, may be induced with various gonadotrophins, the most appropriate being the pituitary extracts known as FSH-P Three days of stimulation with decreasing doses of follicle stimulating hormone (FSH) with increasing luteinizing hormone (LH) content ensures mean ovulation rates of 11.1 in the ewe or 14.2 in the dairy goat, including 20% and 10% non-responses (< 5 corpora lutea (CL)), respectively. In the ewe, prior antigonadotrophic pretreatment results in a significant gain in ovulation rate due to the elimination of non-responses. In the goat, however, the responsiveness to repeated exogenous stimulation is impaired by the immune reaction. As a consequence of superovulation, there is a decrease in spermatozoal survival and/or transport within the donor genital tract which seems to condemn cervical artificial insemination. In the ewe, deposition of 100 x 10(6) fresh spermatozoa in utero 49 h after progestagen sponge removal results in the recovery of 77% viable embryos versus 87% when insemination occurs 32 h after the onset of oestrus. In the goat following deposition in utero of 100 x 10(6) frozen/thawed spermatozoa 45 h after the end of progestagen treatment, the mean fertilization rate is 71% but it reaches 87% for females having their LH surge 15 h before the Al takes place. In this species, the definition of an efficient standardized timing for Al implies a better synchronisation of ovulations. Compacted morulae and/or blastocysts are recovered 5-6 d (sheep) or 6-7 d (goat) after fertilization. Because of the impenetrable cervix, retroflushing of the uterine horns with phosphate buffered saline (PBS) requires a transperitoneal approach. After laparotomy, first recovery rate reaches 72-75% but repeatability is limited, in contrast, laparoscopic recovery, although less efficient in first collection (63%), has been successful up to 7 times. Cryopreservation of pre-hatched embryos is confined to bovine-inspired technology. Using 1.5 mol.l-1 ethylene-glycol as a cryoprotectant and 20% FCS (foetal calf serum) added to PBS-F1 (phosphate buffered saline-F1) medium we obtained 85-90% reanimated embryos, as confirmed by 65% total survival following transfer At least as effective as surgery but easier and quicker, laparoscopic transfer of 2 embryos in each synchronised recipient leads to 65% total survival (80% fertility and 80% surviving embryos in fertile recipients). In conclusion, ET technology which is mainly limited by the productivity of current treatments in term of usable embryos, allows 4-5 products (direct transfer) or 3 products (through deep frozen storage) per donor treatment.