Livestock have long been regarded as a potential source of donor organs to alleviate the global organ shortage for transplantation. Sheep have a similar anatomy to humans, providing the standard model for demonstrating biocompatibility and performance of biological heart valves to obtain regulatory approval for their use in transplantation. Like most mammals, sheep cells contain two well‐characterized carbohydrate epitopes, galactose‐α1,3‐galactose (α‐Gal) and N ‐glycolylneuraminic acid (Neu5Gc), which are absent in humans. Formation of these xenoantigens is catalyzed by two enzymes, namely α1,3 galactosyltransferase (GGTA1) and CMP‐Neu5Gc hydroxylase (CMAH), respectively. Towards generating new sheep models, we used Cas9‐mediated genome editing in both male and female ovine fetal fibroblasts to knockout (KO) both alleles of CMAH and GGTA1 . Selected double KO (DKO) fibroblast strains were used for somatic cell transfer cloning to produce blastocysts that were transferred into gestational surrogate ewes. Following the transfer of 128 male and 40 female cloned blastocysts, six male and eight female lambs were born; however, none of the males survived. Molecular analyses of cells from the five surviving ewes confirmed their compound heterozygous state, resulting in a functional DKO phenotype and subsequent immune rejection of embryonic tissues during natural breeding with wild‐type rams. This new DKO sheep model better mimics the human immune status, offering greater physiological relevance for preclinical testing of biological heart valves, alleviation of red meat allergy syndrome due to the presence of dietary xenoantigens, and a widely culturally acceptable alternative source of certain donor organs.

Background: The study of early mammalian embryonic development is the basis for the cultivation of embryonic stem cells (ESCs), assisted reproductive technology (ART), and understanding and preventing early embryonic developmental defects. Metabolism is the most fundamental physiological activity of embryonic development. Studies have shown that specific metabolic pathways and metabolites play key roles in embryonic development. These roles involve the regulation of signal transduction in addition to the provision of energy to the organism. Aim of Review: This review examines the factors affecting the critical moments of embryonic development, such as oocyte maturation, zygotic gene activation, cell compaction, and two genealogical differentiations. It also presents the characteristics of embryonic metabolism at this time. This review aims to provide new insights and approaches for improving early mammalian embryonic development by clarifying the relationship between embryonic metabolism and its developmental processes. Furthermore, the review emphasizes embryonic metabolism as a potential indicator for assessing the level of embryonic development in vitro, providing a new basis for assessment in assisted reproductive technologies. Key Scientific Concepts of Review: This review is focused on three main key concepts. First, we demonstrate known regulatory mechanisms of embryonic development to enhance the potential of early embryonic development. Second, we elucidate the potential role of metabolic processes and their products in early embryonic development. Third, we provide new foundations and perspectives for the study of the early embryo from the perspective of cellular metabolism.