Characterisation of pregnancy losses after embryo transfer by measuring plasma progesterone and bovine pregnancy-associated glycoprotein-1 concentrations.

The aim of this analysis was to determine whether pregnancy loss (PL) after embryo transfer (ET) in cattle was related to maternal progesterone (P4) concentrations during and shortly after ET, and maternal bovine pregnancy-associated glycoprotein-1 (bPAG-1) concentrations in plasma at days 25-35 of gestation. Embryos (n=260) were produced either in vivo after superovulation (n=115), or in vitro from oocytes (obtained with ovum pick-up) in co-culture (n=44) or cultured in a synthetic medium (n=101). Overall, PL was 56.9% (148) and no significant differences occurred in calving rate among the three embryo production groups. There was no difference in P4 concentrations on days 7-14 of gestation in the three groups, nor between ongoing and interrupted pregnancies. Between days 25 and 35 of pregnancy, bPAG-1 concentrations were unaffected by embryo production, but in cattle that had PL between days 26 and 120, four bPAG-1 profiles could be detected. Between days 25 and 32, bPAG-1 concentrations were influenced by PL, and concentrations were significantly lower in animals in which PL occurred between days 26 and 120 than in those animals that aborted later or calved at term. Early P4 concentrations suggested that maternal luteal factors were not responsible for PL which appeared to be caused by impaired conceptus development (regardless of embryo type) as reflected by low maternal bPAG-1 concentrations prior to embryonic death.