Embryo Transfer in Sheep and Goats
The amount of embryo transfers done in small ruminants are a fraction of those recorded for cattle. Globally, almost 900,000 embryo transfers were reported for cattle in 2012, while only 12,458 were reported for sheep and 1,013 for goats. In addition to commercial and market factors limiting the production of embryos in small ruminants, current embryo transfer techniques in sheep and goats almost exclusively consist of surgical and/or laparoscopic methods for embryo collection and transfer.
Donor and recipients are synchronized using progestagens with an injection of PGF2α given on the day the intravaginal progestagen device is inserted. Because of the additional superovulation hormonal treatment donor females receive, recipients come into estrus earlier than donor ewes and does; therefore, the progestagen source (typically an intravaginal device) in recipients is removed 12 hr before it is removed in donors.
FSH is commonly used to superovulate small ruminants. As in cattle, FSH is commonly administered twice daily in a series of decreasing doses administered over 3 days (eg, day 1 = 5 and 5 mg; day 2 = 3 and 3 mg; day 3 = 2 and 2 mg). On the last day of FSH treatment, the progestagen source is removed and a luteolytic injection of PGF2α given. Estrus is typically detected by vasectomized bucks/rams; artificial insemination should take place 12–24 hr after estrus is detected or 45–50 hr after progestagen removal. Intracervical or transcervical artificial insemination is difficult and requires advanced training and practice. Increased pregnancy rates are obtained by laparoscopic artificial insemination, because it allows the semen to be deposited in the cranial aspect of the uterine horns.
Surgical embryo collection is still very common, but laparoscopic and nonsurgical transcervical catheterization procedures are consistently improving and yielding good results, albeit still lower than those obtained with surgical methods. Embryos are collected 7–8 days after estrus.