Indications for ovariectomy in the mare include removal of benign tumors or to achieve behavioral modification related to estrus. Many surgical approaches and techniques have been described. They include removal under general anesthesia in dorsal recumbency (positioned on the back), standing through the flank, or removal through the vagina with a crushing-type instrument. With the advent of laparoscopic (keyhole) surgery, all other techniques have become relatively dated simply because the laparoscopic approach is minimally invasive, avoids the risk of general anesthesia, greatly improves visualization and access to the base of the ovary and its blood supply (pedicle), and provides a cosmetically superior result with decreased convalescence.
The most common reasons for ovariectomy is removal of benign tumors affecting the ovary called a granulosa thecal cell tumor (GTCT). These tumors are discovered because behavioral aggressive, even stallion like tendencies, are identified toward other horses and people.
Additionally, ovary removal can attenuate persistent signs of estrus (being in season), when other forms of medical and hormonal therapies have been attempted. There is some controversy and difference in opinion regarding the success of this procedure to provide modification in behavior.
Diagnosis is based on recognition of aggressive clinical signs, ovarian palpation and ultrasound and confirmation with blood work evaluating circulating elevated levels of estrogen, testosterone and inhibin.
Postoperatively, the mare is maintained on antibiotics and anti-inflammatories for 2–5 days. The CO2 gas that is used to insufflated or expand the abdomen can sometimes cause a low-grade inflammatory response within the abdomen which may lead to low grade transient fever. This is usually short-lived and resolves within 48 hours. Food is gradually reintroduced over the next few days. Incisions heel within two weeks and horses return to work typically within one month.