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. Laparoscopic (keyhole) removal of ovaries has become a popular alternative as it 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 of aggressive behavior, including stallion like tendencies, 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 elevated levels of anti-mullerian hormone, testosterone and inhibin circulating in the bloodstream.
Postoperatively, the mare is maintained on antibiotics and anti-inflammatories for 2–5 days. Occasionally low-grade fevers result from the inflammatory response resulting from the surgery. 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 (Figure 4).