Embryonic wastage is rampant in cattle during early stages of pregnancy, particularly the first few weeks of gestation, a time recognized for significant remodeling of the embryo. Of particular interest to this laboratory are the first two lineage specification events, trophectoderm (TE) and primitive endoderm (PrE) specification, occurring between days 6 and 8 of gestation. The TE is responsible for uterine attachment and production of interferon-tau (IFNT), the factor of maternal recognition of pregnancy in ruminants. The PrE forms the yolk sac, which provides nutrients to the developing embryo. It is probable that developmental miscues during these differentiation events are responsible for the high rate of pregnancy loss, however, information on these early lineage processes is lacking in ruminants. The objective of the first study was to improve the current methods for detecting IFNT in biological samples. A novel interferon stimulatory response element (ISRE)-reporter assay was created, and provides adequate quantification to measure IFNT. Additionally, it has a shorter completion time than previous bioassays, and does not require the use of a live virus. The second study describes the development of a PrE cell line derived from bovine embryos. The PrE outgrowths can be produced at high rate, and can be maintained in a continuous culture system for about 6 weeks. As a true bovine PrE cell line does not currently exist, these lines hold great potential for the study of early development. Collectively, these studies improve knowledge of bovine embryogenesis, and provide insights that may be used to limit the pregnancy failures occurring in this species.