Effect of timing of progesterone administration on pregnancy rate after embryo transfer in ovariectomized mares.

Ovariectomized recipient mares were divided into two groups. Group A mares received 300 mg progesterone in oil i.m. daily starting 5 days before transfer of a 7-day embryo. Group B mares received the same dose of progesterone, but starting at least 4 days before donor ovulation. Presence of an embryonic vesicle was determined by ultrasonography; mares were considered to be pregnant if they had normal vesicle development to Day 18. Pregnancy rates were: Group A, 6/8; Group B, 1/12 (P less than 0.01). An additional 4 mares in Group B had a vesicle visible at 14 days which degenerated or did not grow. These results indicate that, for establishment of pregnancy after embryo transfer, there is a need for synchrony of donor ovulation with onset of progesterone administration to ovariectomized recipient mares.

Effect of timing of progesterone administration on pregnancy rate after embryo transfer in ovariectomized mares. Academic Article