Mares with granulosa tumors most often display wicked habits such as squealing, biting kicking and exhibiting stallion-like behavior. Mares that have developed cresty necks and voice changes most often retain the characteristics after surgery. Less dangerous mares, but those with irritable, fussy or silly periods every month may be regarded as a nuisance in terms of show, race or ranch work. If a mare is valued, but not for breeding purposes, spaying may provide the necessary alternative to produce a more solid performer. A non-surgical treatment for mares with undesirable estral behavior is the administration of an oral synthetic progesterone, Regumate.
Progesterone is the calming female hormone responsible for maintenance of pregnancy.
Regumate's inhibiting effect on the occurrence of the estrous cycle might provide temporary help during a prospective broodmare's show or race career. If more permanent measures are required, the mare owner must look to surgical alteration. Dr. Robert K. Shideler of Colorado State University's Veterinary Teaching Hospital outlined three methods of removing the ovaries. Major abdominal surgery under general anesthesia is the most expensive method involving the longest recovery period, yet may be the only option available to horse owners in many locations. The ventral midline incision made from the umbilicus toward the udder gives the practitioner easy access to the ovaries.