Delayed blastocyst development is associated with altered metabolism and proteome in male and female bovine embryos†

Developmentally delayed embryos are associated with reduced implantation potential and live birth rates; however, inherent causes of delayed development are not well understood. Metabolism during preimplantation development is responsible for the production of energy and biosynthetic material to support growth, and disturbances to these pathways can reduce embryo viability. The present study utilized electrochemical microsensors to determine differences in rates for oxygen consumption, extracellular acidification, and hydrogen peroxide production between normal and slow-growing, male and female bovine blastocysts. In addition, pooled samples of blastocysts were subjected to proteomic analysis to determine differences in the abundance of proteins associated with metabolism between the sexes and developmental timing status. In comparison to blastocysts developing over a normal timespan, blastocysts forming 1-2 days later had a higher oxygen consumption rate, differences in abundance of electron transport complex proteins, and reduced abundance of biosynthetic enzymes when compared to blastocysts developing during a normal timeline. Embryo sex resulted in unique differences in metabolic enzyme abundance with potentially different contributions to delayed development. In addition, male and female blastocysts had differential protein abundances, indicating differences in metabolic pathway activity. Therefore, embryos that took longer to reach the blastocyst stage of development appeared to have an imbalance between energy production and biosynthetic activity, which could differentially impact male and female embryos.