Predicting pregnancy loss
Pregnancy loss is the pits! The high frequency of pregnancy loss in dairy herds is now realized more than ever before and is extremely frustrating. When pregnancy diagnosis by palpation was the standard practice, commonly done at 35 to 45 days post-insemination, the period of highest risk for embryonic mortality had mostly passed. Not knowing otherwise, it was generally assumed that open cows simply had not conceived.
Nowadays, it is increasingly common to use techniques and tools that allow for earlier pregnancy diagnosis. Diagnosing pregnancy early is beneficial for identifying open cows and allowing for reinsemination strategies that will help minimize days open and increase profitability. However, as more and more herd managers work with these approaches, they are realizing how many of the "open" cows were actually pregnant for a short period of time but lost the pregnancy during early embryonic development—an understandably disturbing realization.
Approximately 30 percent of pregnancies are lost before birth (O'Connor, 2006). The highest percentage of this loss occurs before day 28 of gestation, the time when ultrasound and various chemical tests can be used for pregnancy diagnosis. This early loss may be attributed to problems with embryo development.
Though at a lesser frequency, still more loss occurs after the first month of pregnancy. Frequencies reported in the scientific literature range from 3.2% to 42.7% (Pohler et al., 2016). After day 30, pregnancy failure may relate less to embryo quality and more to development and function of the placenta. Many of the chemical tests designed for early pregnancy diagnosis (e.g. BioPRYN, DG29, IDEXX) measure glycoproteins that are produced by the placenta and circulating in the bloodstream.
A recent research study was conducted with more than 400 pregnant, lactating Holstein cows in Brazil. Ultrasound on day 31 following timed insemination was used to determine pregnancy status. Four weeks later, on day 59 of pregnancy, 12% had lost their pregnancy. An additional 7% lost their pregnancy at later stages before calving. For any herd manager, losing 19% of pregnancies that were originally confirmed is troubling. Of most interest in this study, however, was that circulating concentrations of pregnancy-associated glycoproteins (PAG) on day 31 were higher in the cows that kept their pregnancy between day 31 and 59 (Figure 1). Exploring further, researchers found that it would have been possible, with 95% accuracy, to predict some of the future pregnancy loss by setting a minimum PAG threshold on day 31 (Pohler et al., 2016).
Figure 1.
Relationship between pregnancy-associated glycoproteins (PAG) concentration on day 31 and maintenance of pregnancy until day 59.
How might this information help with management of a dairy herd? In the future, it is certainly possible that diagnostics will be refined enough so that results falling into a "recheck" category will include "high risk" cows that are currently pregnant but should be closely monitored for pregnancy over the following weeks. If a pregnancy is lost, every day counts in managing to re-establish pregnancy so that she may continue to have many productive days in the herd.
