Embryo Transfer: The Last 20 Years
Veterinarian explains some of the trends in embryo transfer use.
by Kasey Brown, associate editor, Angus Journal
STAUNTON, Va. (Oct. 16, 2013) — Embryo transfer (ET) can let breeders improve their herd genetics over time, expand their herd quicker and market individual cow families, said Randall Hinshaw, veterinarian with Ashby Herd Health Service Inc. Speaking at the 2013 Applied Reproductive Strategies in Beef Cattle Symposium (ARSBC) in Staunton, Va., Oct 15-16, he explained some “old truths” from his 30 years of experience in embryo transfer.
The donor is the largest variable in embryo production — not the FSH (follicle-stimulating hormone) protocol, not the practitioner nor the environment, said Randall Hinshaw.
The donor is the largest variable in embryo production — not the FSH (follicle-stimulating hormone) protocol, not the practitioner nor the environment, said Hinshaw. He said it depends upon the follicular wave, and some donors are just suited for superovulation.
The recipient (recip) is the largest variable in the conception rate, not the embryo or the practitioner. However, chance is the largest variable in small groups.
Ultrasound has changed the practice of ET, Hinshaw said. There are many benefits, but the biggest for ET are being able to determine the sex of the fetus, to assess superovulation before breeding, and to understand follicular dynamics.
No matter which protocol is used, there are three tools for synchronization, Hinshaw explained. Prostaglandin administered between Day 5 and Day 20 of the estrous cycle regresses the corpus luteum (CL). Gonadotropin-releasing hormone (GnRH) either resets follicle development or starts the ovulation of a follicle by causing a surge in luteinizing hormone (LH). He noted that donors do not need estradiol anymore, because GnRH does the same thing with similar results. Progestin [melengestrol acetate (MGA) or controlled internal drug release (CIDR®) device] inhibits heat and blocks ovulation. With these tools, it is possible to collect from multiple donors at the same time.
Per collection, he said the average is about eight embryos, though it can range from zero to more than 18.
With frozen embryos, he said to expect 55%-60% pregnancy rates using Grade 1 embryos. Results will be 10%-15% lower with Grade 2 embryos and 20%-30% lower with Grade 3 embryos. Using fresh embryos generally results in pregnancy rates 7%-10% better than with frozen embryos.
Using sorted semen reduces transferable embryos by about 50%, and the availability of sorted semen is bull-dependent. He noted that he has seen better results in virgin heifers, and that splitting embryos improves output. It can also be used with in vitro fertilization (IVF), where a donor’s ovaries are aspirated transvaginally, the oocytes are matured and fertilized in a laboratory dish, and the embryos are then transferred.
Advantages to IVF, it can be done every other week and it works on problem donors. Hinshaw added that valuable semen can be used on multiple donors this way, and he is able to aspirate pregnant cows. However, it is costly, yields lower conception rates, and results in higher pregnancy wastage and more fetal anomalies. Logistics also poses a problem.
Cost of production for ET for one donor can be about $800, with the estimated cost per embryo around $105. With five donors, the cost per embryo is reduced to about $81.
Hinshaw spoke during Wednesday’s ARSBC session focused on current topics in reproductive management. Visit the Newsroom at www.appliedreprostrategies.com to listen to his presentation and to view his PowerPoint slides and proceedings paper. This comprehensive coverage of the symposium is compiled by the Angus Journal editorial team. The site is made possible through sponsorship by the Beef Reproduction Task Force.