Validation of pregnancy associated glycoproteins-based ELISA kits to determine early pregnancy status in lactating Nili-Ravi buffaloes

The objective of the current study was to evaluate pregnancy-associated glycoproteins (PAGs) based enzyme-linked immunosorbent assay (ELISA) kits utilizing whole blood, serum, or milk samples for diagnosis of early pregnancy status in lactating Nili-Ravi buffaloes. Dairy buffaloes (n = 174) of mixed parity, 4-6 years of age, having mean (± standard deviation) days in milk 165 ± 87, and body condition score of 3.26 ± 0.34 were randomly enrolled in this study. Buffaloes were exposed to penile deviated bulls with 12 h interval for estrus detection during peak breeding season and eventually bred naturally at their respective standing estrus (day 0). Blood and milk samples were collected at days 24, 28, and 35 post-breeding to run a rapid visual pregnancy test® (RVPT) as a buffalo-side test or ELISA-based assay in the laboratory to detect early pregnancy status. Transrectal B-mode ultrasonography was performed to diagnose pregnancy at day 35 post-breeding and used as a gold standard to validate results of RVPT or ELISA-based tests. The RVPT is a visual readout test for pregnancy detection and had sensitivity (77.9 vs. 89.7 vs. 93.3%), specificity (77.9 vs. 89.7 vs. 93.3%), and accuracy (84.5 vs. 90.1 vs. 94.2%) at days 24, 28, and 35 post-breeding, respectively. The PAGs were assayed using ELISA kits in serum and had sensitivity (77.9 vs. 89.7 vs. 93.3%), specificity (84.2 vs. 87.7 vs. 93.9%), and accuracy (82.1 vs. 88.4 vs. 93.7%) at days 24, 28, and 35 post-breeding, respectively. Similarly, PAGs were also analysed using ELISA kits in milk samples and had sensitivity (77.6 vs 89.5 vs 95.0%), specificity (89.1 vs 91.9, vs 93.9%), and accuracy (85.1 vs 91.1 vs 94.3%) at days 24, 28, and 35 post-breeding, respectively. Overall, the Kappa values in this study exceeded 0.85 at day 35 post-breeding using RVPT or ELISA-based test kits in serum or milk samples, indicating a high level of agreement between PAGs detection method and gold standard for pregnancy diagnosis. The pregnancy outcomes based on ELISA-based PAGs detection at day ≥28 post-breeding had a high negative predictive value, indicating that the probability of incorrectly administering prostaglandins to pregnant buffaloes would be low if these tests were implemented on a commercial dairy herd. Taken together, it is concluded that PAGs-based determination of pregnancy using RVPT or ELISA in blood, serum, or milk samples can be used effectively for pregnancy diagnosis at ≥28 days post-breeding with more than 90% accuracy in Nili-Ravi buffaloes.