The diagnosis of congenital anestrus is based on the age of the animal and exclusion of all other possible causes (including chromosomal defects, endocrine disorders, and previous oophorectomy). Because cyclicity in queens is determined by photoperiod, lighting conditions should be appropriate for several months before congenital anestrus is diagnosed and exogenous hormones are administered. One reported method to induce estrus in cats is FSH at 2 mg/cat, IM, once daily until signs of estrus appear (not administered for >5 days).
Acquired anestrus may result from previous oophorectomy, exogenous hormonal treatment (including glucocorticoids), profound hypothyroidism, or ovarian disease (cysts or neoplasia). Diagnosis is based on history, physical examination, biochemical evaluation, ultrasonography, and laparotomy.
Prolonged estrus may be caused by ovarian cysts that produce estrogen, functional ovarian tumors, or exogenous estrogens (including human transdermal hormone replacement therapy). Exogenous hormones should be discontinued. Laparotomy with histopathology is usually indicated, because medical attempts at inducing ovulation (human chorionic gonadotropin, FSH, GnRH) are usually unrewarding. Prolonged diestrus can result from luteal cysts in the ovary. Medical manipulation with prostaglandins is usually unrewarding, and ovariectomy with histopathology is indicated.