Merck | Multiple Ovulation, Embryo Transfer and In Vitro Fertilization

Multiple Ovulation, Embryo Transfer and In Vitro Fertilization

Embryo Transfer (ET) is an advanced reproductive technology that can help to quickly multiply the genetics of the top females in a cattle herd.

ET involves specific hormonal treatment of donor cows and heifers to cause multiple follicles to ovulate. Following this superovulation, the donors are bred using artificial insemination (AI), and approximately seven days after insemination, embryos are non-surgically collected or “flushed” from the donor’s uterus. These embryos are then transferred into synchronous recipients who will serve as surrogate mothers. The embryos may also be cryopreserved or frozen to be transferred at a later time. The frozen embryos will be maintained in liquid nitrogen storage vessels until they are thawed and transferred into the cattle.

ET is not as widely used as AI but has contributed substantially to the improvement of the dairy-cattle industry since it was first used in the early 1980s. On a worldwide basis, more than 750,000 embryos are produced annually from superovulated donors and more than 450,000 embryos are produced using in vitro techniques1.

Development of commercial embryo transfer in cattle started in the 1970s for the proliferation of desirable phenotypes. However, the University of Guelph introduced the concept of MOET (multiple ovulation and embryo transfer) in 1987, which resulted in increased selection intensity and reduced generation intervals, and thus, increased genetic gains1.

Embryo transfer is now commonly used to produce AI sires from the top producing cows and bulls. The procedure for embryo transfer in cattle requires two key components:

Generating and Obtaining (Flushing) Embryos from the Donor Female.

The selection of each donor female is one of the most important decisions in ET to justify costs. Mating decisions should be made considering the genetic worth and economic value of the potential calves. The ideal donor female should have:

  • Regular estrus cycles beginning at a young age
  • Conceptions that need no more than two inseminations
  • 14 month or lower calving interval
  • Calvings without difficulty
  • No reproductive abnormalities and disease, and no known genetic defects

Embryo donors must receive good nutrition. Ideally, dairy cows should be flushed after peak lactation when the energy balance has returned to positive, and she has adequate energy reserves.

Superovulation allows cows to ovulate more than one oocyte. Although approximately 20 percent of the females do not respond to the superovulation treatment, this technology has helped to increase prolificacy of selected donor cows and to decrease generation intervals2.

Transferring Each Embryo into a Different Female (Recipient), Which Gestates and Gives Birth to that Fetus.

Embryo sexing is conducted on biopsies collected from embryos before transfer or freezing.

moet and ivf

In Vitro Fertilization (IVF) is another reproductive technology that harvests unfertilized oocytes directly from the ovaries of a donor cow or heifer. These oocytes are fertilized one day after aspiration and transferred seven days after fertilization, being cultured in an environment similar to the cow’s uterus. They are then transferred into recipient cows seven days after the recipient’s standing heat or estrus, which is similar to the transfer process for embryos produced by embryo transfer.

In Vitro Fertilization in cattle allows for more offspring from valuable females, similar to ET. IVF extends the reproductive life of cows that do not respond to superovulation treatment or produce only unfertilized eggs, which allows to keep selected cows within a selection program2.

New genomic techniques are increasingly being used to select donors for embryo transfers, which combined with sexing and freezing technologies, is driving a new era of IVF in the dairy sector3.

References

  1. Mapletoft RJ. SA History and perspectives on bovine embryo transfer.2013. Anim. Reprod., v.10, n.3, p.168-173
  2. Bousquet, D., Burnside, E. B. and Van Doormaal, B. J. 2003. Biotechnologies of reproduction applied to dairy cattle production: Embryo transfer and IVF. Can. J. Anim. Sci. 83: 403–407.
  3. Sirard MA. 40 years of bovine IVF in the new genomic selection context. 2018. Reproduction, 156(1):R1-R7.