Surgery improves mare behavior

New research suggests that removing a mare’s ovaries can have a positive effect on her behavior.
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Colorado State University study suggests that removing a mare’s ovaries can have a positive effect on her behavior.

Horse with pinned ears

After the mares underwent standing laparoscopic surgery to remove both ovaries, their owners reported a 95 percent improvement in behavior.

The researchers reviewed the cases of 27 mares referred to the university clinic for generally poor behavior that was not associated with any stage of the estrus cycle. The most common complaints were “disagreeable demeanor,” and “aggression toward other horses.” The study mares showed no signs of granulosa cell tumors, growths on the ovaries commonly associated with undesirable behaviors, during palpation and ultrasound examination.

After the mares underwent standing laparoscopic surgery to remove both ovaries, their owners reported a 95 percent improvement in behavior, including a reduction in aggression toward other horses. The lowest improvement category was “frequent urination” with 83 percent improvement. Overall, 82 percent of owners say they were “very satisfied” with the outcome of the surgery.

The researchers note that bloodwork done at the time of surgery revealed no association between hormone levels and each mare’s behavior. However microscopic examination of the ovary tissues did yield evidence of early-stage granulosa cell tumors in 33 percent of the mares. This, the researchers say, suggests that the tumors are likely underdiagnosed.

Click here to learn how the seasons affect "marish" behavior. 

The researchers stress that it’s important to rule out other possible physical causes for poor behavior—such as ulcers or poor training—before considering an ovariectomy for a mare.

Reference: “Ovarian histopathology, pre- and post-operative endocrinological analysis and behavior alterations in 27 mares undergoing bilateral standing laparoscopic ovariectomy,” Canadian Veterinary Journal, February 2020. 

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