My mare urinates or squirts every time my daughter rides her in practice and competition on poles and barrels. She has even slowed down so she can urinate when running, and it slows her performance down. We have tried marbles and have now tried an implant. No change other than the mare's attitude and cycles have improved for her. We do not know how to control the urinating issue, as she has just gotten worse in the last two years.

Certainly, urination, or “throwing off,” is a common sign of estrous behavior in mares (commonly referred to as being “in heat”). Typically, mares cycle every 21 days, with estrous behavior lasting five to seven days of that period. For performance horses that exhibit unwanted estrous behavior, such as your mare is doing, a drug known as Regu-Mate® (altrenogest) is typically administered orally daily to lessen such behavior. While marbles or implants may also be common, these are much less effective than Regu-Mate® treatment. Regu-Mate® must be prescribed by your veterinarian. You may also wish to consider having your mare spayed (having her ovaries removed). This would entirely eliminate any estrous behavior, although rendering her unable to carry a foal. Still, for many mares not destined for the broodmare band, this is a good option. Your equine veterinarian can provide you additional information on spaying, should you decide to consider it.
You may also wish to consult your veterinarian if you believe this behavior may not be due to her estrous cycle. Other conditions such as bladder or kidney issues may also cause problems with frequent urination.