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Induction of Abortion in Mares with Prostaglandin F₂¹

University of Wisconsin, Madison 53706

Abstract

Two experiments were conducted to determine if prostaglandin F₂ would cause abortion in mares and to develop a PGF₂-treatment regimen for inducing abortion consistently. In Experiment 1, 22 pony mares, approximately 40 to 150 days pregnant, were randomly assigned to three groups which were given a single injection of one of the following doses of PGF₂ (number of mares): 0 (7), 1.25 (7) or 2.50 mg (8). In Experiment 2, 13 pony mares, approximately 80 to > 300 days pregnant, were given 2.50 mg PGF₂ at 12-hr. intervals until abortion occurred.

In Experiment 1, a single injection of 0, 1.25 or 2.50 mg PGF₂ terminated pregnancy in 0 of seven, three of seven and four of eight mares, respectively. Incidence of abortion was not related to stage of gestation. The interval from injection to abortion was 3, 4 or < 21 days for mares given 1.25 mg PGF₂ and 6, 7, 9, or < 21 days for mares given 2.50 mg PGF₂.A single injection of 1.25 mg or 2.50 PGFZa did not significantly alter rectal temperature or produce any other discernible side effects (e.g., anorexia, :diarrhea, colic or sweating).

In Experiment 2, 13 of 13 mares aborted following injection of 2.50 mg PGFZa at 12 hr. intervals. An average of 3.7 injections (range 1 to 7) were given before abortion occurred; the mean interval from first injection to abortion was 38.6 hr. (range 2 to 79 hr.). One mare did not return to estrus or ovulate following abortion; seven of 13 mares ovulated during the first post-abortion estrus and 12 of 13 mares ovulated during the second postabortion estrus. The mean number of injections before abortion occurred and the mean interval from first injection to abortion was not significantly related to stage of gestation. However, mares that were 80 to 90 days pregnant had a shorter (P < .05) interval from abortion to first estrus (2.0 days) than did mares that were 160 to 180 (25.3 days) or > 300 days pregnant (15.9 days). Similarly, mares that were 80 to 90 days pregnant had a shorter < .05) interval from abortion to ovulation ,,<.5 days) than mares that were 160 to 180 (38.0 days) or > 300 days pregnant (29.3 days).

¹ From the Department of Benerinary Science, University of Wisconsin, Madison 53706. Supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison and by Grant No. 630-0505A from the Ford Foundation and by Public Health Service Training Grant No. 5-TO1-HD-00104-08. Part of these data were presented at the 65th Annual Meeting of A.S.A.S. in Lincoln, Nebraska, July 29 — August 1, 1973. The prostaglandin F₂-tham salt was a gift from Dr. James Lauderdale, Upjohn Company, Kalamazoo, Michigan.

² Predoctoral Trainee, Endocrinology-Reproductive Physiology Program, University of Wisconsin, Madison.