Review: Some challenges and unrealized opportunities toward widespread use of the in vitro-produced embryo in cattle production

Abstract

The embryo produced by in vitro oocyte maturation, fertilization, and embryonic development is an important resource for genetic improvement and has the potential to improve female fertility and to be programmed to produce offspring with superior ability for health and production. The cultured embryo is also an important component of several realized and potential technologies such as gene editing, somatic cell nuclear cloning, stem cell technologies and gamete generation in vitro. Full realization of the opportunities afforded by the in vitro-produced embryo will require overcoming some technical obstacles to cost-effective implementation of an embryo transfer program. Among the research goals for improving the penetration of embryo transfer in the cattle industry are development of methods to increase the supply of oocytes from genetically elite females, enhance the proportion of oocytes that become transferrable embryos, improve the fraction of embryos that establish pregnancy after transfer, reduce pregnancy wastage after pregnancy diagnosis, and identify culture conditions to optimize postnatal phenotype.

Keywords: Assisted reproduction; Embryo culture; Embryo transfer; In vitro production; Oocyte maturation.

Fig.1.

Overview of the procedures for embryo transfer in cattle using in vitro-produced embryos. None of the steps shown here have been optimized. Among the major bottlenecks to optimization of the system are insufficient supplies of oocytes, low rates of production of transferrable embryos from matured oocytes, lower than expected rates of pregnancy establishment, and high loss of pregnancies before calving. The figure was produced using biorender.com.

Fig. 2.

Importance of the period of oocyte maturation and fertilization for the establishment of competence of an embryo to develop to the blastocyst stage. Effects of the in vitro environment on oocyte maturation, fertilization and embryonic development were assessed for the percent of embryos developing to the blastocyst stage and the survival of the blastocysts after vitrification and thawing. Events occurring in vitro are indicated by the petri dish while events in vivo, either in heifers or sheep, are shown by the animal icons. The figure was produced using data from Rizos et al. (2002) and is reproduced from Hansen (2020b) with permission of Annual Reviews.

Fig. 3.

Selected experiments that illustrate (A) pregnancy rate at day 30 of gestation following embryo transfer vs following artificial insemination (total n = 2 874), (B) pregnancy rate at day 30 to day 35 of gestation following transfer of a multiple ovulation embryo transfer (MOET) or in vitro-produced (IVP) embryo (total n = 1 189), and (C) pregnancy rate at day 41 of gestation following the transfer of a MOET or IVP embryo (total n = 8 295). Recipients were lactating dairy cows (A and C) or crossbred beef cows (B). Abbreviations: TAI = timed artificial insemination; TET = timed embryo transfer. Results for A, B, and C are from Oliveira et al. (2019), Pontes et al. (2009), and Ferraz et al. (2016), respectively.

Fig. 4.

Pregnancy loss after initial pregnancy diagnosis in cows as affected by the type of pregnancy. Pregnancy loss was calculated for the period indicated above each set of bars. Recipients were lactating dairy cows (A–C) or crossbred beef cows (D). The total number of cows that were initially pregnant was 143 (A), ~427 (B), 2 845 (C), and 814 (D). Abbreviations: AED = automatic estrous detection device; ET = embryo transfer; IVP = in vitro produced; MOET = multiple ovulation embryo transfer; TAI = timed artificial insemination; TET = timed ET. Results for A, B, C, and D are from Stewart et al. (2011), Marques et al. (2020), Pereira et al. (2016), and Pontes et al. (2009), respectively. Note that the study indicated in B used a mixture of IVP and MOET embryos.

Fig. 5.

Programming of 205-day adjusted weaning weight in Brahman calves by addition of choline chloride to culture medium for in vitro-produced embryos. Abbreviations: Cho = choline; Veh = vehicle. The increase in weaning weight due to choline, which was significant, averaged 20 kg (a 9% increase). Data are from Estrada-Cortés et al. (2021a).