Factors associated with pregnancy-associated glycoprotein (PAG) levels in plasma and milk of Holstein cows during early pregnancy and their effect on the accuracy of pregnancy diagnosis

Abstract

Lactating Holstein cows (n = 141) were synchronized to receive their first timed artificial insemination (TAI). Blood and milk samples were collected 25 and 32 d after TAI, and pregnancy status was determined 32 d after TAI using transrectal ultrasonography. Cows diagnosed pregnant with singletons (n = 48) continued the experiment in which blood and milk samples were collected and pregnancy status was assessed weekly using transrectal ultrasonography from 39 to 102 d after TAI. Plasma and milk samples were assayed for pregnancy-associated glycoprotein (PAG) levels using commercial ELISA kits. Compared to ultrasonography, accuracy was 92% for the plasma PAG ELISA test and 89% for the milk PAG ELISA test 32 d after TAI. Plasma and milk PAG levels for pregnant cows increased from 25 d to an early peak 32 d after TAI. Plasma and milk PAG levels then decreased from 32 d after TAI to a nadir from 53 to 60 d after TAI for the plasma PAG assay and from 46 to 67 d after TAI for the milk PAG assay followed by an increase from 74 to 102 d after TAI. Overall, plasma PAG levels were approximately 2-fold greater compared with milk PAG levels, and primiparous cows had greater PAG levels in plasma and milk compared with multiparous cows. The incidence of pregnancy loss from 32 to 102 d after TAI based on ultrasonography was 13% for cows diagnosed with singleton pregnancies, and plasma and milk PAG levels decreased to nonpregnant levels within 7 to 14 d after pregnancy loss. Both plasma and milk PAG levels were negatively correlated with milk production for both primiparous and multiparous cows. We conclude that stage of gestation, parity, pregnancy loss, and milk production were associated with plasma and milk PAG levels after TAI similarly. Based on plasma and milk PAG profiles, the optimal time to conduct a first pregnancy diagnosis is around 32 d after AI, coinciding with an early peak in PAG levels. Because of the occurrence of pregnancy loss, all pregnant cows should be retested 74 d after AI or later when plasma and milk PAG levels in pregnant cows have rebounded from their nadir.

Effect of manipulating progesterone before timed artificial insemination on reproductive and endocrine parameters in seasonal-calving, pasture-based Holstein-Friesian cows

“…Treatment did not affect (P = 0.58) PAG levels; however, PAG levels were greater (P < 0.01) from 25 to 36 d after TAI for cows diagnosed pregnant versus not pregnant 39 d after TAI, and were greater (P < 0.02) from 25 to 36 d after TAI for pregnant primiparous versus pregnant multiparous cows ( Figure 5). Variation in PAG concentrations among individual cows during early gestation (Ricci et al, 2015) may have precluded the detection of a treatment effect. The effect of parity and pregnancy status in the present experiment agree with results from an experiment in which stage of gestation, parity, pregnancy loss, and milk production were associated with plasma and milk PAG levels after TAI in Holstein dairy cows (Ricci et al, 2015).…”

“…Variation in PAG concentrations among individual cows during early gestation (Ricci et al, 2015) may have precluded the detection of a treatment effect. The effect of parity and pregnancy status in the present experiment agree with results from an experiment in which stage of gestation, parity, pregnancy loss, and milk production were associated with plasma and milk PAG levels after TAI in Holstein dairy cows (Ricci et al, 2015). …”

“…Altering P4 before or after AI could in turn alter embryonic growth, thereby affecting maternal recognition of pregnancy or pregnancy loss. It is now possible to indirectly assess conceptus development 15 to 22 d after AI by measuring mRNA expression of interferon-stimulated genes (ISG) in circulating blood leukocytes (Stevenson et al, 2007;Gifford et al, 2008;Green et al, 2010) and by measuring pregnancy-associated glycoprotein (PAG) levels in blood or milk samples beginning approximately 25 d after AI (Green et al, 2000;Ricci et al, 2015).…”

Early pregnancy diagnosis using a commercial ELISA test based on pregnancy-associated glycoproteins in Holstein-Friesian heifers and lactating cows

“…Furthermore, plasma PAG levels in heifers were significantly higher than those in lactating cows. Because PAGs can be detected in milk (27) and there was a negative correlation between plasma PAG levels and milk yield (28), lower plasma PAG levels in lactating cows may be explained by the removal of PAGs from the plasma owing to their excretion in milk.…”

Markers of pregnancy: how early can we detect pregnancies in cattle usingpregnancy-associated glycoproteins (PAGs) and microRNAs?

“…Perhaps even more interesting are the effects of parity and sire on PAG concentrations. Heifers have consistently been reported to have the greatest PAG concentration and as parity increases, mean PAG concentration subsequently decreased in a somewhat linear fashion until the 3 or 4th parity (Lobago et al, 2009;Ricci et al, 2015;Pohler et al, 2016b). Recent work has examined sire differences on PAG concentration due to the paternal influence over trophoblast and placental development.…”