Ovarian response to hCG in the postweaning sow

Five non-cyclic postweaning sows were given intramuscularly 1,000 IU of hCG on day 2 (4 sows) and day 36 (1 sow) after weaning. Single or multiple follicular cysts were developed in ovaries in all cases. Plasma E2 fluctuated at low levels in 4 of 5 sows resulting in silent heat. The sows which exhibited neither estrus nor ovulation after hCG administration did not display any preovulatory LH surge, and plasma progesterone levels remained low (< or = 1 ng/ml). These results suggest that abnormal follicular growth or impairment of the ovulation process as a consequence of unsatisfactory LH release after hCG treatment in swine with ovarian inactivity may promote the formation of ovarian cysts.