In vitro production significantly reduces metabolic differences among bovine embryos

Although the in vitro production of bovine embryos now exceeds in vivo production, the quality of in vitro-produced embryos remains inferior. Metabolomic analysis of the spent culture medium used for embryos is considered a relevant source of markers for subsequent developmental capacity, genetic status and sex. However, little is known about the sources of variability in this metabolome and their respective significance.

We compared bovine embryo spent culture media from in vivo developed (IVD) and in vitro produced (IVP) embryos, and analyzed how they varied with embryo stage, grade and sex.

Embryos were produced in vitro under two different conditions: SOF medium supplemented with 1% fetal calf serum or IVF Bioscience media, or developed in vivo. They were recovered at Day-6 and cultured individually for 26 hours. The culture medium was analyzed using 1H-NMR spectroscopy, and the embryos were staged, graded and sexed.

In vitro production significantly reduced inter-embryo variability of the 24 metabolites measured. The mean variance of metabolite content was 5 to 10 times lower in IVP than in IVD embryos (depending on the IVP conditions). IVD embryo stages and grades at the start or end of the culture period contributed to 8% to 18% of variability in the media content, but only 1% of variability for IVP embryos. IVD embryo stage at the start of culture significantly impacted metabolite content. IVD embryo sex did not globally impact composition of the spent culture medium, but the kinetics of decrease of about half of the metabolites differed between male and female blastocysts.

Standardization of the metabolic properties of IVP embryos invites new questions regarding the impact of embryo biotechnology. Differences in metabolism between male and female IVD embryos are highly transient during the morula-blastocyst stages.