Relationship between plasma progesterone and pregnancy-associated glycoprotein concentrations during early pregnancy in dairy cows

The relationship between the concentration of plasma progesterone (P4) during embryo attachment or at recognition of pregnancy, and that of pregnancy-associated glycoprotein (PAG) was assessed in dairy cows. The outcome of artificial insemination (AI) was classified as positive (AI+), negative (AI 12), or late embryonic mortality (EM) by measuring circulating PAG concentrations and by ultrasonography. Based on P4 concentrations at either day 21 or day 15, AI+ and EM cows were classified into \u2018low\u2019 (P4 concentrations mean) P4 groups. In both experiments, the threshold of P4 concentration between the \u2018low\u2019 and \u2018high\u2019 groups was approximately 6 ng/mL. PAG concentrations were lower in the \u2018low\u2019 group only when P4 concentrations were below the threshold. The study findings suggest that a possible P4 threshold exists below which PAG secretion may be impaired