Abstract
Reproduction in ruminant species is a highly complex biological process requiring a dialogue between the developing conceptus (embryo-fetus and associated placental membranes) and maternal uterus which must be established during the peri-implantation period for pregnancy recognition signaling and regulation of gene expression by uterine epithelial and stromal cells. The uterus provide a microenvironment in which molecules secreted by uterine epithelia and transported into the uterine lumen represent histotroph, also known as the secretome, that are required for growth and development of the conceptus and receptivity of the uterus to implantation by the elongating conceptus. Pregnancy recognition signaling as related to sustaining the functional lifespan of the corpora lutea, is required to sustain the functional life-span of corpora lutea for production of progesterone which is essential for uterine functions supportive of implantation and placentation required for successful outcomes of pregnancy. It is within the peri-implantation period that most embryonic deaths occur in ruminants due to deficiencies attributed to uterine functions or failure of the conceptus to develop appropriately, signal pregnancy recognition and/or undergo implantation and placentation. The endocrine status of the pregnant ruminant and her nutritional status are critical for successful establishment and maintenance of pregnancy. The challenge is to understand the complexity of key mechanisms that are characteristic of successful reproduction in humans and animals and to use that knowledge to enhance fertility and reproductive health of ruminant species in livestock enterprises.