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Luteolysis Following a Single Injection of Prostaglandin F₂ in Sheep¹

University of Wisconsin, Madison 53706

Abstract

Twenty-eight ewes were assigned randomly to seven groups (four ewes each) and six of the groups were injected, intramuscularly on day 8, with one of the following doses of prostaglandin F₂ (PGF₂): 0 (vehicle only), 1, 2, 4, 6, or 8 mg (Experiment 1). Ewes in the remaining group were untreated. In a second project (Experiment 2), four groups of ewes (four ewes each) were given intramuscular (IM) and intrauterine (IU) injections on day 8 as follows: 1) vehicle IM, vehicle IU (controls); 2) 2 mg PGF₂ IM, vehicle IU; 3) 6 mg PGF₂ IM, vehicle IU; or 4) vehicle IM, 2 mg PGF₂ IU.

In Experiment 1, injection of either 6 or 8 mg PGF₂ IM shortened (P < .05) the mean length of the treatment estrous cycle and the interval from day 8 to return to estrus. Mean lengths of these two end points were not significantly different among the other five groups (control, 0, 1, 2, or 4 mg). Length of the post-treatment estrous cycle was not significantly altered by PGF₂ treatment.

In Experiment 2, average corpora lutea (CL) weight was less(P < .05) for each of the groups treated with PGF₂ than for the control group. However, the average CL weight was less (P < .05) in ewes given 6 mg PGF₂ IM (group 3) or 2 mg PGE₂ IU (group 4) than in ewes given 2 mg PGE₂ IM (group 2). Average CL weight did not differ significantly between group partial 3 (6 mg IM) and 4 (2 mg IU). The luteolytic effect of PGF₂ was more pronounced when given locally (IU) than when given systematically (IM).

¹ From the Department of Veterinary 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-T01-HD-00104-08.

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