New Technologies for Pregnancy Determination

How to Use Them to Better Manage Your Herd

By George Perry, Ph.D. Texas A&M University

As feed costs increase, the expense to maintain non-pregnant cows through the winter also increases, and these expenses must be paid for by the calves that are born and weaned the following year. For example, in a herd of 200 cows and winter costs of $500 per cow; 12 non-pregnant cows kept through the winter would cost an additional $6,000. This would increase the cost for each of the 188 calves born by $31.92. Thus, at minimum, pregnancy status should be determined on all cows following the breeding season.

Pregnancy diagnosis has traditionally been performed by a local veterinarian using rectal palpation. However, many advances in pregnancy determination have occurred over the last few decades, and other methods to determine pregnancy include transrectal ultrasonography and blood sampling. Each technique has its benefits and its limitations; therefore, each method should be evaluated based on your operation and your access to each technology.

Methods Of Pregnancy Determination

Rectal palpation

Rectal palpation (the time-honored method) has been used by veterinarians since the early 1900s.14 A skilled veterinarian can determine a pregnancy between 30 and 35 days after conception2 and can accurately estimate the age of the fetus.8 This method is performed by manually feeling through the rectal wall for the amniotic vesicle, fetus, placentomes, or a “membrane slip.” This method gives immediate results, but accuracy is dependent on the skill of the veterinarian. There can be incidences of embryonic loss due to rectal palpation, but these losses vary tremendously between technicians.1

Transrectal Ultrasonography

Transrectal ultrasonography technology has become more routine as the portability and durability of equipment has increased. Similar to rectal palpation, a probe is inserted into the rectum and placed over the uterus. The probe emits sound waves that bounce back differently depending on the density of the object (fluid appears black and bone appears white). A skilled clinician can detect a pregnancy as early as 27 days after conception.3,5 As with rectal palpation, results are known immediately. Furthermore, a skilled clinician who is properly trained can determine age, viability (presence of a heartbeat), and gender of the fetus.5,10 Similar to rectal palpation, accuracy is dependent on the skill of the clinician, and there are additional upfront costs of the equipment.

Chemical Pregnancy Determination

Recognition of the fetus by the dam occurs around day 15 to 16 after insemination12 through a chemical signal, but this chemical signal is not detectable in the circulating blood. However, when the embryo begins to attach to the uterus, binucleated cells in the placenta migrate and fuse with the epithelial cells that line the uterus.15 These binucleated cells synthesize proteins that are released into the maternal blood supply. One of the protein types synthesized is pregnancy-associated glycoproteins (PAG). These PAG proteins can be detected in maternal circulation beginning approximately 25 days after conception.7 Multiple laboratory and one chute-side test is available to determine pregnancy status based on presence of PAGs in maternal circulation. Unlike the previous methods (rectal palpation and transrectal ultrasonography) where a skilled clinician is required, a chemical test only requires a blood sample be collected.

One question that is often asked is how accurate are chemical pregnancy detection methods, and why do they sometimes

Key Points

• Methods for determining pregnancy status exist and include; rectal palpation, transrectal ultrasonography, blood sampling, and observation for return to estrus.

• Rectal palpation and transrectal ultrasonography give immediate results, but the accuracy is dependent on the skill of the veterinarian.

differ from palpation and/or ultrasonography? To answer the first part of the question, commercially available assays are very accurate at detecting PAGs in circulation above a specific threshold. The bigger question is why can they differ from palpation and/or ultrasonography? As has been mentioned previously, accuracy of palpation and/or ultrasonography is based on the skill of the technician. A large study comparing different commercially available PAG tests to transrectal ultrasonography performed on the same day are present in Table 1.9. As reported, high levels of agreement (> 90%) occurred between all tests, but why the disagreements? Ultrasonography is not perfect, and embryos can be missed. Thus, ultrasonography can call an animal open when in fact she is pregnant, and PAG assays can detect PAGs and call her pregnant. In addition, PAGs have a long half-life, and thus can be detected in circulation after an embryo dies. If an embryo dies and is not visualized by ultrasonography, a PAG assay can still call the animal pregnant for a period of time.6 False Negatives occur when PAG concentrations are not in sufficient quantities to call an animal pregnant, but an embryo or embryonic tissue is visualized on the ultrasound. Recent research has indicated that animals with decreased circulating concentrations of PAGs on day 30 have increased incidence of embryonic mortality.13 Variation among PAG assays occur in how they are read (human error) and which PAG or PAGs are being detected. In short, no test is perfect. When we compare imperfect tests, there will be discrepancies between them, but when comparing commercially available PAG assays to a welltrained technician, agreement between them is very high.

Utilizing Pregnancy Status To Better Manage Your Herd

• Chemical or blood tests require the ability to collect a blood sample. (303) 539-9300

Everyone is aware of the traditional reasons for determining which cows are pregnant at the end of the breeding season: timely culling of open cows, selling animals that conceived late in the breeding season, decreasing winter feed costs, etc. However, when we think about pregnancy determination as a reproductive technology and how it can impact overall herd management, there are several reasons to not only determine which cows are pregnant but also when they conceived during the breeding season.

There are definite advantages to grouping cows based on expected calving date, such as the ability to focus time and labor,