Estrus,Ovulation,Progesterone and Luteinizing Hormone after Prostaglandin F 2α in Mares 1

Abstract

Summary

After a control estrous cycle, 10 mg PGF_2α was deposited in the uterus in six mares (300-500 kg; 3-20 yr) at 7-9 days after ovulation. Blood plasma progesterone fell from 13.6 to 5.8 ng/ml within 12 hr and to 0.9 ng/ml at 48 hr after PGF_2α, estrus began in 2.2 days and ovulation occurred at Day 5.8 of estrus. The estrus after PGF_2α persisted longer than estrus in control cycles (7.5 vs 5.2 days; P < 0.05), but the interval from ovulation to the end of estrus was unchanged (1.6 vs 1.5 days). An increase in blood plasma LH began the day before estrus and continued past ovulation; LH declined beginning 2 days after ovulation and continuously for 8 days. A control estrous cycle after the PGF_2α cycle resembled in every measurement the control cycle before PGF_2α, indicating no carry-over effect of PGF_2α. Subcutaneous injection of 15 mg PGF_2α 7-9 days after ovulation also caused luteolysis, estrus, and ovulation — resembling in every detail the comparable events after intrauterine PGF_2α. We conclude that PGF_2α given sub-cutaneously or into the uterus is a powerful luteolysin with no carry-over effect on subsequent control estrous cycles in mares.