Pregnancy diagnosis in cattle using pregnancy associated glycoprotein concentration in circulation at day 24 of gestation

Cattle producers are limited to day 28-30 of gestation as the earliest time point for accurate pregnancy diagnosis due to the effectiveness of ultrasound and chemical based methods, including commercially available pregnancy associated glycoproteins (PAG) tests. The objective of the current studies were to determine if early gestation circulating PAG concentrations at day 24 could be used to diagnose pregnancy in dairy cattle undergoing embryo transfer. In vitro produced embryos were transferred into Holstein x Gir cows and heifers on day 7 following ovulation. Study 1 utilized only cows (n = 101) determined to be pregnant on day 24 of gestation by progesterone concentration, as well as CL and PAG presence. In study 2, animals were not predetermined to be pregnant and both heifers (n = 111) and cows (n = 242) were used. In both studies, blood was collected at day 24 for PAG analysis as well as day 31. Final pregnancy confirmation occurred on day 60 via transrectal ultrasonography. Serum PAG concentrations were quantified using an in house PAG ELISA. Following timed embryo transfer (TET) in study 1, of the 101 cows diagnosed as pregnant on day 24, 80 cows were identified as still pregnant on day 31 of gestation (77%). Study 2 had a pregnancy rate at day 31 of 33.7% of total embryos transferred. Mean circulating PAG concentration at day 24 differed (P < 0.001) between animals diagnosed pregnant and non-pregnant at day 31 in both studies (study 1, 2.964 ± 0.262 ng/mL vs 0.946 ± 0.168 ng/mL and study 2, 1.962 ± 0.261 ng/mL vs 0.731 ± 0.109 ng/mL). Concentration of PAG between pregnant and non-pregnant cows in study 1 and 2 was significant, however, pregnant heifers in study 2 (1.562 ± 0.266 ng/mL) had concentration of PAGs that only had a tendency to differ compared to non-pregnant heifers (non-pregnant, 0.799 ± 0.290 ng/mL; P = 0.0669). Only animals that were pregnant at day 31 were analyzed in late embryo mortality analysis (heifers, n = 54; cows, n = 159), defined as pregnancy loss between day 31 and 60. Between day 31 and 60, 39 (12 in study 1 and 28 in study 2) animals experienced late embryo mortality. Circulating concentrations of PAG were not significantly different (P > 0.05), in either study, at day 24 of gestation in animals that maintained pregnancy until day 60 compared to animals that lost pregnancy between day 31 and 60 (late embryo mortality, LEM). In summary, early gestation circulating PAG concentration may have application in diagnosing pregnancy at day 24 of gestation and more work is needed to determine the potential of early gestation PAGs in predicting embryo loss in dairy.