By Jerica Rich and George Perry
Early pregnancy diagnosis and being able to identify AI sired calves from calves sired by clean-up bulls is crucial for maximizing herd productivity and increasing economic return from your cows. Current methods for pregnancy diagnosis include: observation for return to estrus, rectal palpation, transrectal ultrasonography, and most recently blood tests for specific antigens. Blood tests to detect pregnancy are of interest because they can be more cost effective, as they do not require the specialized equipment or specialized training. The specific antigens in blood that these tests detect are called pregnancy-associated glycoproteins (PAGs) and they can be used to determine pregnancy status as early as 28 days post-breeding. Pregnancy associated glycoproteins originate from the placenta and can be detected in the cow’s blood after the conceptus attaches to the uterus. Based on this knowledge multiple blood tests for early detection of pregnancy in cattle are now commercially available.
If you are thinking of switching to using blood tests to determine pregnancy a few important questions arise. Will this test be as accurate as a trained professional using transrectal ultrasonography? Will this test detect early embryonic loss? With these questions in mind, a recent retrospective study was conducted at South Dakota State University to determine the accuracy and abilities of these tests. Two commercially available blood tests were analyzed in comparison to transrectal ultrasonography conducted 28-40 days post AI, blood samples were collected at the time of ultrasonography, in a total of 12 herds.
Both blood tests were able to determine pregnancy status at 28 days post-AI, or shortly after the conceptus attached to the uterus. Additionally, these tests were able to separate AI pregnancies from natural service pregnancies when AI pregnancies were at or greater than 28 days and natural service pregnancies were less than 25 days. Both pregnancy detection blood tests were also in very good agreement with transrectal ultrasonography, with the both tests producing results similar to ultrasonography in the percent of cows correctly identified as pregnant or open. Both pregnancy tests were also sensitive enough to retrospectively detect differences in PAG concentrations among animals that experienced embryonic loss. However, most of these animals would have been classified as pregnant at time of sample collection. Therefore, the use of these blood pregnancy tests to predict embryonic loss in cattle is not suggested.
In a production setting several options are available to determine pregnancy status in cattle. The mentioned study demonstrated that commercially available blood tests can be used to determine AI conception rates as early as 28 days post-AI with a single blood sample and without the need for specialized equipment. However, before switching to solely blood-based pregnancy testing it is important to assess the various pros and cons and evaluate whether this truly is the right move for your operation. With blood-based pregnancy tests there is no need to palpate early pregnant cows and heifers, effectively removing the need for specialized equipment. Conversely, by using rectal palpation and/or transrectal ultrasonography many reproductive structures can be monitored to diagnosis other reproductive problems that may be occurring. Furthermore the age of the fetus can be determine to allow for grouping of animals to better manage labor at calving.
Therefore, the most practical application of these blood-based pregnancy test might be for determining AI conception rates (~28 days after AI), and then to follow up by having your veterinarian determine pregnancy after the breeding season has concluded. This way cows can be grouped based on gestational age, additionally at this time other reproductive concerns based on any embryonic loss that may have occurred can be determined. Thus combining this technology with the expertise of your local veterinarian can improve the overall reproductive efficiency in your herd.