Molecular Regulation of Post-Hatching Embryo Development: Implications for Early Pregnancy Losses in Livestock Species.

Pregnancy loss (PL) remains a major limitation to reproductive efficiency in livestock, with a substantial proportion originating during early embryo development, particularly between blastocyst hatching and implantation. This developmental window encompasses complex processes of lineage differentiation and morphogenesis. Accumulating evidence indicates that intrinsic defects in embryonic development, most notably within the epiblast, are key contributors to PL, especially following in vitro embryo production. Mechanistic investigation of this period has historically been limited by reliance on resource-demanding in vivo approaches. In this review, we summarize current knowledge on the molecular regulation of early embryo development in ungulates and the factors associated with PL during the post-hatching period. We further synthesize recent advances in molecular technologies, extended embryo culture systems, and three-dimensional endometrial models that are transforming the study of post-hatching embryo development in livestock species. Collectively, these advances provide a foundation for refining assisted reproductive technologies and developing predictive strategies to mitigate PL, thereby enhancing reproductive efficiency and sustainability in livestock production systems.