American Association Of Veterinary State Boards (AAVSB) Practice Exam

The key event is a surge of luteinizing hormone from the anterior pituitary. As the maturing follicle secretes increasing amounts of estrogen, this rising estrogen creates a positive feedback on the hypothalamic–pituitary axis, producing a sharp spike in LH release. That LH surge acts on the dominant follicle to cause rupture and release the oocyte—the moment of ovulation. The oocyte completes meiosis I to become a secondary oocyte and is released with surrounding cells. After ovulation, LH also promotes the transformation of the ruptured follicle into the corpus luteum, which begins producing progesterone to prepare the reproductive tract for potential pregnancy. Estrogen’s rise helps prepare the cycle and supports the LH surge, but the actual trigger for ovulation is the LH surge. FSH supports follicle growth earlier but does not directly trigger ovulation.