The Effect of Unilateral Ovariectomy on Plasma Gonadotropin Levels, Estrus and Ovulation Rate in Sheep

Abstract

The phenomenon of compensatory hypertrophy of ovarian weight and ovulation rate following unilateral ovariectomy was used to examine a possible role for the gonadotropins, LH [luteinizing hormone] and FSH [follicle stimulating hormone], in affecting follicle growth and ovulation rate in the ewe. During the breeding season FSH levels increased (P < 0.05) during the period 5 1/2 to 12 h following unilateral ovariectomy performed on either day 14 or 16 of the estrous cycle. When unilateral ovariectomy was performed on day 14 ovulation rates were fully compensated at the next estrus, whereas compensation in ovulation rate was incomplete when unilateral ovariectomy was carried out on day 16. Twelve to fourteen days after the estrus following laparotomy, ovarian weights (less the weight of corpora lutea) had increased (P < 0.05) in both groups. Both ovarian weight (12-14 days after laparotomy) and FSH levels (within 24 h of laparotomy) did not increase significantly over controls when unilateral ovariectomy was performed during the anestrous season. Ovulation rate can be determined within the 3 days prior to the onset of estrus. Support is given to the hypothesis that FSH levels, particularly around day 14, are important in determining ovulation rate at the next estrus.