Factors affecting ovarian compensation after unilateral ovariectomy in gilts

Two experiments were conducted to identify the temporal limits of an ovarian compensatory response after unilateral ovariectomy (ULO) in gilts and to examine ovarian and hormonal factors that might be related to this response. In the first study, all eight gilts that were unilaterally ovariectomized on d 12, 14 or 16 of an estrous cycle and two of four ULO on d 18 had a significant compensatory increase in ovulation rate per ovary compared with controls. Ovulatory compensation failed to occur, however, in two of four and four of four gilts ULO on d 18 or 19 of an estrous cycle, respectively. In the second study, blood samples were collected from 26 gilts beginning on d 14 of an estrous cycle, and animals were assigned to sham-surgery or ULO on d 17, 18 or 19. Ovarian compensation occurred after ULO on all 3 d of surgery in the second study, but most follicles failed to ovulate and formed large luteinized cysts. The ability to compensate was related positively to the number of medium-sized follicles on the intact ovary at the time of ULO, to an increase in concentrations of follicle-stimulating hormone 12 to 18 h after ULO and to the interval from ULO to the preovulatory surge of luteinizing hormone. In a third experiment, interruption of the ovulatory mechanism and development of cystic follicles similar to those observed in the second study were induced simply by physical manipulation of the d 19 preovulatory ovary while contralateral untouched ovaries ovulated normally.