Effects of repeated daily injections of prostaglandin F2alpha on ovaries in mares.

In experiment 1, seven groups of pony mares (2 or 3/group) were given either no injections (controls), or 5 (5X) or 10 (10X) daily subcutaneous (SC) injections of 1.25 mg PGF2alpha beginning on days 1, 7 or 13 post-ovulation. Compared to controls (24.5 days), the interovulatory interval was longer (P less than ..05) for day 7, 10X (33.5 days) and day 13, 10X mares (49.0 days) but was not different for the remaining groups. In experiment 2, nine groups of pony mares (4/group) were given either no injections (controls) or 1 (1X) or 10 (10X) daily SC injections of 1.25 mg PGF2alpha beginning on day 2 of estrus or on days 1, 7 or 13 post-ovulation. Compared to controls (25.0 days), the interovulatory interval was longer (P less than .05) for day 13 post-ovulation, 10X mares (40.0 days) and shorter (P less than .05) for day 1 post-ovulation, 10X mares (14.5 days). The interovulatory interval for the remaining groups was no different (P less than .05) from that for controls. In day 13 post-ovulation, 10X mares, the longer interovulatory interval did not appear to be related to a depression in either peripheral LH concentration (no effect of treatment on LH) or can follicular development (no effect of treatment on diameter of largest follicle). This suggests that circulating levels of gonadotropins were adequate for ovarian follicular development and ovulation and the effect of repeated dialy injections of PGF2alpha in preventing ovulation was likely exerted at the ovarian level directly on the follicle.