Cellular mechanisms of implantation in domestic farm animals

In order for pregnancy to be established, the conceptus of domestic animals must signal its presence upon arrival in the uterus, a process known as maternal recognition of pregnancy. The conceptus derived signal(s) prevent(s) the structural and functional demise of the corpus luteum to ensure the maintenance of a uterine environment that supports implantation and embryonic development. Implantation is a remarkable event that has been described as a biological paradox because an adhesive interaction is formed between two apical surfaces of epithelial cell types that are typically covered by non-adhesive glycoproteins. In domestic animals (such as pigs, horses, sheep, does and cows), the implantation process is not invasive as it is in most other mammalian species. This review describes the interaction between the conceptus (embryo and surrounding membranes) and the uterine epithelial surface in domestic farm animals and ability of the conceptus to control the lifespan of the corpus luteum to maintain pregnancy.