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The spayed mare Reine with her owner Jennifer O’Bray Photo courtesy Jennifer o’Bray


winter. The hormonal status of the spayed mare will mostly likely be that of a mare in winter. A mare in winter anestrous (a sexually inactive period) and a spayed mare will have no progesterone or estrogen in her bloodstream.”


On the other hand


Dr. Yarbrough suggests trying Regu-Mate first.


If the synthetic progesterone causes changes in the mare’s behavior, the mare is a candidate for spaying. Unlike other species, horses show sexual receptivity because they lack progesterone and receive high levels of estrogen. The dominate follicle builds, ovulates, releases the egg and what is left is the corpus luteum that produces progesterone which makes the lining of the uterus thick for implantation and for a healthy pregnancy.


The corpus luteum produces progesterone until the placenta takes over production. If the egg is not fertilized, the corpus luteum dies, progesterone production stops and she displays sexual behavior. “We encourage people to try for 60 to 90 days


to determine if the signs are related to hormonal fluctuations,” says Dr. Yarbrough. “Generally we tell people that if the mare gets better on Regu-Mate, you can expect 90% of what you saw on the Regu-Mate when you spay.” The expectation will not be 100% because the elevated


progesterone level of Regu-Mate has a sedative effect. Secondly, after an ovariectomy, the mare may still be affected by hormonal influences from the uterine body.


Final Thoughts Dr. Pavicic reminds people considering the procedure, “There has to be a clear reason to do it. You can’t go into it lightly. Due diligence has to be done. Investigate and determine why she might behave the way she does. Rule out physical problems like a cyst. And if you go ahead with the operation and then sell the mare, you have the obligation to tell the people who buy her.” Removing a mare’s ovaries is a permanent method of


changing her estrous cycle and possibly her behavior in a positive manner. She will likely be the personality she was before the surgery, but in a consistent manner.


56 July/August 2011


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