Trophoblastic vesicles and maternal recognition of pregnancy in mares.

Research has indicated that trophoblastic vesicles (TV) formed from Day-14 equine conceptuses would prolong luteal maintenance in mares after surgical transfer to the uterus at Day 10 after ovulation. The current study assesses TV as a further model for maternal recognition of pregnancy in mares. The objectives of the study were to determine the ability of TV to prolong luteal maintenance in mares, their effect on endometrial production of prostaglandin F (PGF) in vitro, and their ability to secrete polypeptides in vitro. In contrast to our previous study (Ball et al., 1989b), transfer of TV from Day-12 or -14 equine conceptuses to recipient pony mares at Day 10 or 12 post ovulation did not significantly prolong luteal maintenance compared to sham-operated control mares. Prolonged luteal maintenance was noted in 1/10 control mares and 1/15 mares that received TV. Trophoblastic vesicles from Day-14 conceptuses significantly reduced production of PGF by Day-14 pregnant endometrium in vitro. However, intact Day-14 conceptuses failed to reduce PGF secretion in the same culture system. TV secreted an array of polypeptides that were similar in molecular weight range to those produced by intact conceptuses or conceptus fragments at Day 12 or 14. Although this study failed to confirm our earlier finding that TV prolong luteal maintenance in recipient mares, this study does indicate that TV may be a useful model for evaluating maternal recognition of pregnancy in mares.