An investigation into the effects of cow genetic background and pasture-based management system on circulating pregnancy-associated glycoprotein concentrations during early pregnancy.

Cows with greater circulating pregnancy-associated glycoprotein (PAG) concentrations after artificial insemination (AI) are more likely to maintain pregnancy (i.e., less pregnancy loss). The objective was to evaluate the effect of cow genetic background and feeding level on circulating PAG during early pregnancy in seasonal-calving, pasture-based, lactating dairy cows. Three divergent genetic groups (GG) of dairy cows were enrolled: Elite Economic Breeding index (EBI) Holstein-Friesian cows (Elite), representative of the top 5% nationally; average EBI Holstein-Friesian cows (NA), representative of the national average in Ireland; and purebred Jersey (JE) cows, representative of Jersey genetics available in Ireland and used primarily for crossbreeding. The 3 GG were evaluated under 3 contrasting spring-calving pasture-based feeding treatments (FT): control (CTL), low grass allowance (LGA), and high concentrate (HC). A total of 108 cows (36 in each GG and each FT) were initially enrolled. Cows were artificially inseminated following detected estrus at the start of the seasonal breeding period, and if cows did not return to estrus, blood samples were collected on d 23, 25, and 28 after AI (n = 92 samples collected; 16 cows returned to estrus before d 23). Ultrasound examinations for pregnancy diagnosis were conducted on d 30 to 36 after AI (hereafter referred to as d 33); if pregnant, cows were re-examined on d 60 to 66 after AI (hereafter referred to as d 63). Plasma PAG concentrations were measured using an IDEXX kit, and pooled blood from Holstein-Friesian cows that were on d 35 ± 2.4 (mean ± SD) of gestation was used to create a standard curve. Blood PAG concentrations were expressed relative to the concentration in the pooled sample from pregnant cows (% PC). There was evidence of an effect of GG on the PAG profile observed during early gestation. Jersey (n = 21) cows had greater mean (95% CI) plasma PAG concentrations compared with Elite (n = 20) cows but not NA (n = 13) cows: 52.1% PC (39.5%, 66.8%), 32.0% PC (22.5%, 43.5%), and 36.3% PC (24.3%, 51.4%), respectively. There was no effect of FT on circulating PAG concentrations. Across all cows sampled, circulating PAG concentrations were greater in cows that subsequently maintained their pregnancy (n = 54) compared with cows that subsequently had pregnancy loss (n = 9), and concentrations were lowest in cows that had no evidence of pregnancy based on plasma PAG measurements in advance of ultrasound diagnosis on d 33 (n = 29). Overall, the study findings indicate that cow genetic background and feeding treatment had little effect on circulating PAG concentrations during early pregnancy in grazing dairy cows. Pregnancy-associated glycoprotein determination on d 23 to 28 after AI could aid identification of pregnancy status and future risk of pregnancy loss.