Many trainers and riders believe that some performance mares have a decrease in performance when they come into heat. Today we are going to talk about options for controlling heat to help with their behavior. Generally, mares are on a 21-day cycle with mares being in heat about 5 to 7 days of this period. Some mares show no abnormal symptoms as far as performance while others are very difficult to train or show when in heat due to behavioral changes. However, it is important to make sure the changes are due to estrus and not another problem, and this can be difficult to determine in some cases. 

It is important to have your equine vet perform a complete lameness and neurological exam to be sure there is no other problem. Any kind of pain with the back or legs could cause the same symptoms. Even low-grade tying up could be involved. Mares with ovarian tumors will exhibit stallion-like behavior, so a reproductive exam is a must. Controlling estrus in these horses is difficult and most options are ineffective. Removing the ovaries will generally cure the problem, although some mares without ovaries can still show heat. Also, removing the ovaries prevents any future breeding. The most commonly used treatment is daily administration of Regu-Mate, a progestagen compound that is somewhat effective but must be given daily and is expensive. Another treatment to prevent heat is to place a large glass marble in the uterus to make the mare’s system think she is pregnant. Although this treatment was effective in one study, it has actually had limited success in practice. Growth implants for cattle have also been used to control heat in mares, although studies have shown them to be mostly ineffective for this purpose.