Development of a new radioimmunoassay by using antiserum against pregnancy-associated glycoprotein II : concentrations in holstein dairy cattle .

Bovine pregnancy-associated glycoproteins (boPAG) can be classified into two main subfamilies: the boPAG–1 and the boPAG–2 groups. RIA systems allow quantifying boPAG-1 molecules in pregnant cattle. Concerning boPAG-2, as no radioimmunoassay was developed, its quantification in peripheral blood of pregnant cows remains to be investigated.
The present work aimed to develop a new heterologous RIA allowing the measurement of boPAG-2 concentrations in bovine species.
A total of 77 Holstein dairy cows were used for this study. They were bled at Days 45, 90, 120, 150, 180, 210 after AI, at parturition and at Day 30 postpartum. Polyclonal antiserum against boPAG-2 (AS438) was raised in New Zealand rabbits. Due to the instability of boPAG-2 molecule, we used boPAG-1 (67 kDa) as standard (dilutions ranging from 100 to 0.8 ng/mL) and for iodination with 125-I isotope. The optimal dilution for primary AS438 was 1:1,1500.
Mean concentrations of boPAG-2 increased continuously from Day 45 of pregnancy (0.78 ± 0.07 ng/mL) reaching a peak at Day 210 (32.78 ± 3.02 ng/mL). Thereafter, they decreased until parturition (7.73 ± 0.59). Lower PAG concentrations were observed at Day 30 postpartum (3.62 ± 0.31 ng/mL).
In conclusion, boPAG-2 profile differed from boPAG-1. In general, concentrations of boPAG-2 reached lower values, with no dramatic increase being observed at peripartum period. Due to the lower postpartum concentrations, it is expected that this new RIA can be available for pregnancy diagnosis of cows inseminated in early postpartum, minimizing the risk of false positive concentrations due to the previous pregnancy.