Predicting Embryo Presence and Viability

Abstract

Pregnancy establishment, followed by birth of live offspring, is essential to all mammals. The biological processes leading up to pregnancy establishment, maintenance, and birth are complex and dependent on the coordinated timing of a series of events at the molecular, cellular, and physiological level. The ability to ovulate a competent oocyte, which is capable of undergoing fertilization, is only the initial step in achieving a successful pregnancy. Once fertilization has occurred and early embryonic development is initiated, early pregnancy detection is critical to provide proper prenatal care (humans) or appropriate management (domestic livestock). However, the simple presence of an embryo, early in gestation, does not guarantee the birth of a live offspring. Pregnancy loss (embryonic mortality, spontaneous abortions, etc.) has been well documented in all mammals, especially in humans and domestic livestock species, and is a major cause of reproductive loss. It has been estimated that only about 25-30% of all fertilized oocytes in humans result in birth of a live offspring; however, identifying the embryos that will not survive to parturition has not been an easy task. Therefore, investigators have focused the identification of products in maternal circulation that permit the detection of an embryo and assessment of its well-being. This review will focus on the advances in predicting embryonic presence and viability, in vivo.

Markers of pregnancy: how early can we detect pregnancies in cattle usingpregnancy-associated glycoproteins (PAGs) and microRNAs?

“…Accurate positive pregnancy diagnosis varied between 60 and 100% for milk progesterone, however detection of non-pregnant animals varied between 81 to 100% (Nebel et al, 1987;Sasser, 1987, Nebel, 1988. Longer luteal phases in some cows, cysts or persistent follicles may play a role in elevated progesterone concentrations during the pregnancy test period that yield false positive results (Pohler et al, 2015a). Some discrepancies exist in evaluating the effectiveness of progesterone testing with regards to embryo loss.…”

“…They concluded that a IFNT-stimulated gene based pregnancy test would be possible for heifers at day 18 but not for cows whose response is more limited based on the current sensitivity of available assays (Green et al, 2010). Unfortunately, ISGs are not unique to pregnancy which limits their use as a pregnancy detection tool to identifying nonpregnant animals (Han et al, 2006;Gifford et al, 2007;Pohler et al, 2015a); however, a resynchronization protocol can be implemented in cows that are identified as non-pregnant which improves operation efficiency (Lucy et al, 2011).…”

“…Between 18 and 22 nucleotides in length, miRNAs play important roles in regulation of gene expression and have been found in biological fluids ranging from serum and amniotic fluid to urine and milk (Reid et al, 2011;Pohler et al, 2015a). MicroRNAs are released from cells of most tissue types in plasma membrane bound extracellular vesicles (EV), especially exosomes.…”

“…Contact between the maternal and fetal interface at the microvilli junction allows migration of BNC's towards the basement membrane to begin Wathes, 1980, Wooding andBurton, 2008). Products of BNC's, including hormones, placental lactogen and pregnancy associated glycoproteins (PAGs), are packaged in secretory granules and enter maternal circulation across the basement membrane (Pohler et al, 2015a).…”

“…Loss of pregnancy may occur at any time between conception and calving; however, some time points are more critical than others. Pregnancy failure affects all cattle; however, high producing dairy cattle are more susceptible to decreased pregnancy rates than dairy heifers and beef cows (Diskin et al, 2011;Pohler et al, 2015a;Pohler et al, 2016a, b). Although fertilization rate in cattle is often greater than 85% (Santos et al, 2004, Diskin andMorris, 2008) there have been reports of differences in fertilization rates in beef and dairy cattle that result in a large amount of reproductive failure (Breuel et al, 1993, Sartori et al, 2002Santos et al, 2004Santos et al, , 2009; however, the focus of this review will be on post fertilization failure and detection.…”