In Vitro Production of Bovine Embryos

The natural reproductive cycle in cattle typically results in the birth of one calf per year at best.  Therefore, assisted reproductive techniques (ART) as in vitro production of bovine embryos are used to enhance the reproductive efficiency of animals (Plourdea et al., 2012).

Therefore these procedures have gained increasing importance in the livestock and food industry as they facilitate the production of offspring with superior genetic conditions (Gonçalves et al., 2001; Camargo et al., 2006; Rodríguez-Martinez, 2012), leading to improved animal health and higher quality of the final product.

However in vitro embryo production (IVP) involves various ART procedures that vary among laboratories and species.

Therefore it essentially comprises the following steps:

1. in vitro collection and maturation (IVM) of female gametes (oocytes),
2. preparation and capacitation of male gametes (spermatozoa),
3. in vitro fertilization (IVF) process, either through the co-culture of gametes or assisted microinjection of a spermatozoon into the oocyte,
4. embryonic culture (EC) to allow zygotes to reach the desired developmental stage, typically the blastocyst stage.

The transfer of embryos, referred to as “in vivo” (ET), involves a classic technology developed over three decades ago.

This method includes the superovulation treatment of a donor cow, aiming to induce the release of not just one or two oocytes, as occurs physiologically, but up to 10-15 times more.

Subsequently, the cow is inseminated, and seven days later, embryos at the 7-day stage (morula or blastocyst) are extracted.

They are termed “in vivo” embryos as they remain in the donor cow throughout until recovery, at which point they are immediately transferred to a recipient (fresh transfer) to continue gestation until parturition.

However, they may be frozen and preserved for later transfer (post-thaw transfer).

Ultimately, this technique, whose dissemination and application increased until the late ’90s, has stabilized in Europe since the beginning of the last century.

Between 1999 and 2009, an average of 477 superovulations were performed annually in Spain, resulting in 2,300 “in vivo” embryos.

In 2010, 17,855 donors were flushed in Europe, yielding a total of 119,342 transferable embryos.

This stagnation is partly attributed to the fact that, despite significant efforts invested in improving each step (donor selection, synchronization and superovulation, flushing technique, embryo assessment, recipient selection and synchronization, evaluation of recipients, and transfer technique), the percentage improvements in results are now very limited.

Until 2010, the yield remained around 4.8 transferable embryos in the bovine species.

Challenges such as non-responsive females to superovulation treatments, the need to respect rest periods between consecutive collections, and the requirement for donors to be in perfect gynecological condition hinder substantial improvement in ET results compared to the present day (Herradón et al., 2007).