Observations on the influence of exogenous gonadotrophins and cloprostenol on ovulation in gilts

We studied the effects of gonadotrophins and prostaglandin (PG) F(2alpha) on ovulation in gilts. Twenty-eight gilts were induced to ovulate using 750 IU pregnant mares serum gonadotrophin (PMSG) and 500 IU human chorionic gonadotrophin (hCG), administered 72 h apart. At 34 and 36 h after hCG, gilts received injections of either 500 mug or 175 mug PGF(2alpha) (cloprostenol), or had no injections. Laparotomies were performed at 36 h (cloprostenol gilts) or 38 h (controls) after hCG injection. The ovaries were examined and the proportion of preovulatory follicles that had ovulated (ovulation percent) was determined at 30 min intervals for up to 6 h. The number of gilts in which ovulation was initiated and the ovulation percent increased (p<0.001) with time, but was not affected by treatment. Many medium sized follicles (