© American Dairy Science Association, 2007. Accuracy of a Pregnancy-Associated Glycoprotein ELISA to Determine Pregnancy Status of Lactating Dairy Cows Twenty-Seven Days

To determine the accuracy of a pregnancy-associated glycoprotein (PAG)ELISA in identifying pregnancy sta-tus 27 d after timed artificial insemination (TAI), blood samples were collected from lactating Holstein cows (n = 1,079) 27 d after their first, second, and third post-partum TAI services. Pregnancy diagnosis by transrec-tal ultrasonography (TU) was performed immediately after blood sample collection, and pregnancy outcomes by TU served as a standard to test the accuracy of the PAG ELISA. Pregnancy outcomes based on the PAG ELISA and TU that agreed were considered correct, whereas the pregnancy status of cows in which preg-nancy outcomes between PAG and TU disagreed were reassessed by TU 5 d later. The accuracy of pregnancy diagnosis was less than expected when using TU 27 d after TAI (93.7 to 97.8%), especially when pregnancy outcomes were based on visualization of chorioallantoic fluid and a corpus luteum but when an embryo was not visualized. The accuracy of PAG ELISA outcomes 27 d after TAIwas 93.7, 95.4, and 96.2 % for first, second, and third postpartum TAI services, respectively. Statistical agreement (kappa) between TU and the PAG ELISA 27 d after TAI was 0.87 to 0.90. Pregnancy outcomes based on the PAGELISA had a high negative predictive value, indicating that the probability of incorrectly ad-ministering PGF2α to pregnant cows would be low if this test were implemented on a commercial dairy. Key words: transrectal ultrasonography, pregnancy-associated glycoprotein, pregnancy diagnosi