Effects of prostaglandin F2alpha on the oestrous cycle and pregnancy in mares.

Several experiments indicated that prostaglandin F2alpha (PGF2alpha) has luteolytic and abortifacient properties in mares. A single subcutaneous injection of 1-25 mg PGF2alpha on Day 6 of dioestrus was as effective as 10 mg PGF2alpha in inducing luteolysis. Oestrus and ovulation appeared to be synchronized when a single injection of 1-25 mg PGF2alpha was given on Days 7, 10 or 13 after ovulation but not on Days 1 or 4 after ovulation or on Day 2 of oestrus. Intramuscular administration was as effective as subcutaneous administration and 1-25 mg PGF2alpha was the minimal effective systemic dose to induce luteolysis. Administration of PGF2alpha into the uterus or directly into the CL did not improve the luteolytic efficacy of the intramuscular injection of PGF2alpha. All thirteen mares aborted following injections of 2-5 mg PGF2alpha at 12-hr intervals; an average of 3-7 injections were given before abortion occurred.