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Embryonic mortality: Novel models for predicting the loss
Embryonic mortality (EM) is generally considered to be the primary factor limiting conception rates in cattle and occurs early (< day 28) or late (≥ day 28) during gestation (day 0 = estrus). In cattle, the incidence of early EM is approximately 25% and the incidence of late EM is approximately 3.2 to 42.7% (Vasconcelos et al., 1997; Cartmill et al., 2001a,b; Lamb, 2002). Significant effort has been directed towards understanding the mechanisms resulting in early EM; however, relatively little is known about the causes or mechanisms associated with late EM, most of which occurs around the time of placentation (days 35 to 40). Mechanisms associated with reproductive loss around the time of placentation may be associated with inadequate placental development or function. Binucleate trophoblast cells constitute 15-20% of the ruminant placenta trophoblast population, appear around d 19-20 of gestation in cattle and secrete bPAGs along with other products. Bovine PAGs are commonly used to diagnose pregnancy success in cattle and have recently been reported to be a potential marker of late embryonic mortality in Bos taurus cattle (Pohler et al., 2013). Therefore, we conducted a large experiment to examine the relationship between circulating concentrations of bPAGs in Nelore beef cows (Bos indicus) and late EM. Furthermore, we developed a model to identify animals that will experience EM. Based on positive and negative predicative value analysis, we have identified circulating concentrations of bPAG that are 95 % accurate in predicting EM (between d 28 - d 100) at d 28 of gestation. In summary, based on the experiments, bPAGs seem to be a good marker for predicting EM between d 28 to 100 of gestation and suggest that this model could help elucidate the molecular, cellular, and physiological mechanisms responsible for late EM. Advancements in our understanding of the mechanisms associated with embryonic mortality may lead to development of strategies to overcome these reproductive losses.
Keywords:
cattle, pregnancy, placenta