The horse has two ovaries, located behind the kidneys. The ovaries release reproductive hormones that regulate the estrous cycle and sustain pregnancy. Evaluation of ovarian function is done by history, physical examination, rectal examination, imaging with ultrasound, and hormonal testing. Changes in the size of the ovaries can be categorized into three broad categories:

  • Enlargement of one or both of the ovaries: tumors (e.g.: granulosa cell tumor, cystadenoma), hematomas, cysts, pregnancy
  • Small ovaries: hyperadrenocorticism (Cushing’s disease), poor nutrition
  • Abnormal function: persistent luteal follicles, anovulatory follicles