Comparison of Two Methods of Bovine Pregnancy Tests to Determine Embryonic Loss in Beef Cows

Blood tests to determine pregnancy status as early as 28 days post-breeding based on circulating concentrations of pregnancy-associated glycoproteins (PAGs) are currently available for use in the beef industry. The objective of this study is to determine the accuracy associated with determining early embryonic loss based on visual observation of color change and optical density (OD) using the IDEXX bovine pregnancy test and the IDEXX rapid visual test. Beef cattle from 6 different herds were synchronized using a recommended CIDR based protocol. Pregnancy status was first determined by transrectal ultrasonography between day 32 to 42 post-breeding and blood samples were collected from pregnant animals at this time (n = 492). A final pregnancy determination was performed after the end of the breeding season to determine embryonic loss. Each serum sample was examined in duplicate using the IDEXX Bovine Pregnancy Test and the IDEXX Rapid Visual Test. The results from both the bovine pregnancy test and the rapid visual test were analyzed using a microtiter plate reader. Additionally, the rapid visual test was individually scored and evaluated by two technicians unaware of pregnancy status or embryonic loss. The scoring system consisted of yes/no and a numerical value (0-3) based on color compared to negative and positive controls. Data was analyzed using the GLIMMIX procedure of SAS with herd as a random variable. Overall there were 28 (5.7%) animals that lost an embryo. The bovine pregnancy test indicated decreased circulating concentrations of PAGs in animals that lost an embryo (P = 0.01; 2.45 ± 0.11 vs 2.74 ± 0.04 OD). With the rapid visual test both technicians visually scored the animals that lost an embryo lower compared to animals that did not lose an embryo (P < 0.01; 2.77 ± 0.6 vs 2.93 ± 0.01 and 2.78 ± 0.06 vs 2.96 ± 0.03 for technician 1 and 2, respectively). However, of the animals that lost an embryo only two were identified as not pregnant by the rapid visual test, and of the animals that maintained their embryo only one was falsely identified as not pregnant (0.2%). In summary, both bovine pregnancy tests were sensitive at detecting differences in circulating PAGs among animals that experienced embryonic loss, but the majority of these animals would have been classified as pregnant at time of sample collection.