Plasma pregnancy-associated glycoprotein and progesterone concentrations in pregnant Assaff ewes carrying single and twin lambs

Ovine pregnancy-associated glycoprotein (oPAG) and progesterone (P4) concentrations were monitored weekly during the last three months of gestation and the first month postpartum in plasma of twelve Assaf ewes. The oPAG levels were determined with a heterologous RIA using bovine PAG as standard and tracer and rabbit antiserum against oPAG. The P4 levels were measured with a radioimmunological procedure with a sensitivity to less than 0.1 ng/ml. The oPAG profiles in ewes carrying a single lamb and in those carrying twins were very similar from week 9 of gestation to lambing. Ewes which had twins presented numerically higher oPAG concentrations from week 12 to lambing, but that difference was only significant (p<0.05) at week 21. Ewes carrying twins presented higher (P<0.05) P4 concentrations from weeks 12 to 20 of gestation than those carrying a single lamb, but afterwards there was no difference. No correlation was found between P4 and oPAG concentrations at each stage of gestation studied in any group. After lambing, P4 levels dropped rapidly in one week, whereas oPAG decreased in four weeks to basal values in both groups of ewes. No relationship (P>0.05) was found between oPAG concentrations and lamb birth-weight at any week of gestation considered in this study. However, the lamb birth-weight was positively correlated (P<0.10) with the P4 concentrations from weeks 9 to 19 of gestation. Results indicate that number of fetuses could influence the oPAG production in ewes during the last three months of gestation.