Comparison of Two Serum Pregnancy Tests in Detection of AI Versus Natural Service Pregnancies in Beef Herds

Pregnancy-associated glycoproteins (PAGs) are produced from the bovine trophoblast and can be detected in the blood of pregnant cows. The objective of this study was to compare the accuracy of blood tests compared to transrectal ultrasonography in determining AI pregnancies in beef cattle. Beef cows and heifers from 6 different herds (n = 460) were synchronized using a recommended CIDR based protocol. All cows were maintained separate from bulls for 10 to 15 days after AI. Pregnancy status was determined using transrectal ultrasonography between 28 and 40 days following AI, and at this time blood samples were collected from all animals. 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 (BPT) and the Rapid Visual Test (RVTOD) were analyzed using a microtiter plate reader. Additionally, the Rapid Visual Test was individually scored and evaluated by two technicians unaware of pregnancy status. The scoring system consisted of yes/no (RVTY/N) and a numerical value (0-3) based on the color compared to negative and positive controls (RVTscore). Cohen’s kappa statistics were calculated to assess the agreement between each test and transrectal ultrasonography. Agreement was extremely high for the BPT (0.86), RVTscore (0.85), and RVTY/N (0.86). However, there was only good agreement for RVTOD (0.64) when the OD threshold was set at any reading darker than the negative control. There was no difference (P = 0.79) in the sensitivity (pregnant correctly diagnosed pregnant) of the assays (97%, 97%, 97%, and 96% for BPT, RVTOD, RVTscore, and RVTY/N). There was a difference (P < 0.01) in the specificity (nonpregnant correctly diagnosed nonpregnant) of the assays (88%, 64%, 87%, and 90% for BPT, RVTOD, RVTscore, and RVTY/N) and in the overall percent correctly identified (93%, 84%, 93%, and 93% for BPT, RVTOD, RVTscore, and RVTY/N). In conclusion, both the Bovine Pregnancy Test and the Rapid Visual Test were effective at accurately determining pregnancies >28 days after AI and were in extremely high agreement with transrectal ultrasonography. In addition these assays were able to separate AI pregnancies from natural service pregnancies when AI pregnancies were >28 days and natural service pregnancies were <25 days. However, if a plate reader is used with the Rapid Visual Test a greater threshold reading for pregnancy needs to be used to increase the accuracy of the assay.