Role of progesterone in mobility, fixation, orientation, and survival of the equine embryonic vesicle.
Luteal progesterone was removed by an injection of prostaglandin F2alpha or bilateral ovariectomy on Day 12 of pregnancy in pony mares. The embryonic vesicle remained mobile in the uterus until loss occurred on Days 13, 13, 15, or 19 in four prostaglandin-treated mares and Days 15, 17, 19, or 26 in four ovariectomized mares. Exogenous progesterone given daily, starting on Day 12, maintained pregnancy until Day 40 in five of five prostaglandin-treated and three of four ovariectomized mares. During two-hour mobility trials on Day 14, embryonic vesicles in mares without luteal or exogenous progesterone (n=9) moved to a different uterine segment less frequently (mean number of location changes per two-hour trial: 7.2+/-1.0 vs 10.4+/-1.1, P<0.05) and were observed more often in the uterine body (14.9+/-2.9 vs 8.9+/-1.3, P<0.10) compared to vesicles in mares with a progesterone influence (n=15). Of mares that still had a vesicle present on Day 18, fixation occurred by Day 17 in all (12/12) mares under the influence of luteal or exogenous progesterone but failed to occur in the three mares that were not under progesterone influence. Progesterone replacement was started on Day 16 in three mares that received prostaglandin F2alpha on Day 12 and still had a vesicle on Day 16. The vesicle was maintained and continued to develop in all three mares, indicating that the vesicles were viable four days after PGF2alpha treatment. However, fixation tended to be delayed (P<0.15) and orientation of the embryo proper was altered (P<0.005) compared to mares that were continuously under the influence of progesterone. The results demonstrated the importance of luteal progesterone to mobility, fixation, orientation, and survival of the embryonic vesicle.
Kastelic
J P
JP
Department of Veterinary Science, University of Wisconsin, Madison, WI 53706, USA.
Adams
G P
GP
Ginther
O J
OJ