Developing replacement heifers that get pregnant and maintain pregnancy

Abstract Text:

Reproductive failure is one of the most substantial barriers to profitability in dairy herds. Management issues, cow infertility, bull infertility, heat stress, embryonic mortality and poor heifer development are all contributing factors to reproductive inefficiency. Developing heifers that successfully establish and maintain a pregnancy, give birth to live offspring and stay in the herd for a number of years is critical. In addition to proper selection of these heifers, minimizing reproductive inefficiency, specifically embryonic mortality (EM) is vital. Embryonic mortality is generally considered to be the primary factor limiting conception rates in cattle and occurs early (< day 25) or late (≥ day 25) during gestation (day 0 = estrus). In cattle, the incidence of early EM is approximately 25% and the incidence of late EM is varied, approximately 3.2 to 42.7%. However, in heifers these numbers are thought to be decreased but still a major issue. 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. 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 pregnancy associated glycoproteins (PAGs) 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 dairy cattle (Pohler et al., 2015). Based on positive and negative predicative value analysis, we have identified circulating concentrations of PAG that are 95 % accurate in predicting EM at d 28 of gestation. This talk will highlight some of the work our group as well as others are focusing on wtih regard to selecting high fertility heifers as well as management strategies to decrease reproductive loss in those heifers using PAG testing.  In summary, based on the experiments and relevant literature, PAGs seem to be a good marker for predicting EM but also may provide a useful tool for selection of high fertility heifers. 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, embryonic mortality