(248) A Matched Case-control Study to Investigate the Associations Between Different Pregnancy-associated Glycoproteins and Pregnancy Loss in Multiparous Lactating Dairy Cows

Thainá Minela¹; Alisson Santos²; Gabriela Dalmaso de Melo¹; Ky G. Pohler¹; J. Richard Pursley²

1. Department of Animal Science, Texas A&M University, College Station, USA

2. Department of Animal Science, Michigan State University, East Lansing, USA

Abstract Text:

Trophoblast cells positive for pregnancy-associated glycoproteins (PAG) initiate the process of conceptus attachment to the endometrium lining. This process is key to placentation and results in intense disruption to the architecture of the endometrial luminal epithelium. During this process, PAGs are released into maternal circulation and can be quantified with ELISA assays. There are various commercially available assays, utilizing different combinations of antibodies. Characterization of within-cow daily pregnancy-specific protein B (PSPB; a group of PAGs quantified with the bioPRYN assay) revealed that delayed increase and decreased PSPB concentrations in maternal circulation were phenotypes incompatible with successful pregnancy. The current study aimed to investigate whether other PAGs are predictors of pregnancy loss in a selected population. We hypothesized that level and timing of increase in PAG-21 concentrations are associated with pregnancy loss in multiparous lactating dairy cows. To test this, a set of serum samples from multiparous lactating dairy cows (n = 68) were selected from three randomized complete block design studies. The current study was designed as a matched case-control. “Cases” (n = 30) were cows that experienced pregnancy loss up to 36 days in gestation, while “controls” (n = 30) maintained pregnancy during this period. Cases and controls were also matched based on having early (n = 22) or late (n = 38) PSPB increase (< 22 or ≥ 22 days). To aid comparisons, non-pregnant cows (n = 8) were included in the analyses. All cows were artificially inseminated (AI) following synchronization programs. Daily serum samples were collected between days 18 and 28 post-AI. Concentrations of PSPB (ng/mL) were determined in the previous studies with the commercial ELISA bioPRYN. Concentrations of PAG-21 (ng/mL) were quantified with an in-house ELISA that utilized a combination of mono and polyclonal antibodies (Pohler lab, TAMU). Pregnancy status was determined with ultrasound on days 33, 34, or 36 post-AI. Analyses were performed with PROC MIXED and LOGISTIC of SAS 9.4. Data is shown as means±SEM. The concentrations of PSPB were greater in cows that lost (2.5 ± 0.51) or maintained pregnancy (2.9 ± 0.40) in comparison with non-pregnant (0.2 ± 0.08) counterparts starting on day 23 post-AI (P ≤ 0.04). From days 24 to 28 post-AI, cows that lost pregnancy had lower PSPB concentrations than cows that maintained pregnancy (P < 0.01). Compared to non-pregnant cows, cows that maintained pregnancy had greater concentrations of PAG-21 on day 25 post-AI (5.9 ± 0.93 vs. 1.1 ± 0.29; P = 0.04), while cows that lost pregnancy had greater concentrations of PAG-21 on day 27 post-AI (6.8 ± 0.01 vs. 1.2 ± 0.21; P = 0.03). Cows that experienced pregnancy loss had decreased PAG-21 concentrations from days 26 to 28 post-AI compared to cows that maintained pregnancy (P ≤ 0.04). Based on means comparisons with non-pregnant cows, PAG-21 increased in maternal circulation later compared to PSPB (day 23 for PSPB and days 25 and 27 for PAG-21). In conclusion, PAG-21 concentrations were a significant predictor of pregnancy loss on days 26 to 28 post-AI (P ≤ 0.048). The observed temporal divergence between PSPB and PAG-21 profiles suggests that different PAGs may play distinct physiological roles during early gestation in cattle. A later increase in PAG-21 concentrations in maternal circulation, concurrent with the period of placentation onset, makes PAG-21 a candidate marker of proper placenta development and function.