What are sterile mare horses?

They are quite rare and are still just called mares, or sometimes spayed mares. Because of the difficulty (and danger) of performing major abdominal surgery on such a large animal, mares that are deliberately sterilised because of hormonal imbalances or for another reason (such as to stop breeding) are usually spayed with a laparoscope. A small cut is made in each side, often under local anaesthetic, and the ovaries are removed but the uterus left in place.