Last Updated on February 19, 2022 by Allison Price
You notice your mare becoming more cranky as the days get longer and you anticipate more riding time. You should be careful with her pinched ears and difficulty under saddle. She will occasionally stomp her feet and make a lot of noises without any apparent reason. While you may wonder if she is hurt or ill, it’s clear that she’s probably in heat. She exhibits typical mare-like behavior due to increased activity in her reproductive system.
It’s reassuring to know that she will soon return to normal. You might wonder what you can do to help her get through hormonal swings that can lead to physical discomfort and fuel unfavorable behavior. There are many medical treatments that can help. Experts point out the advantages of conscientious management to reduce the stress of estrus. It’s important to understand your mare’s internal workings before you can decide the best course of action for you and your mare.
The Biological Basics
Many species of female mammals have a cycle of reproduction that includes a period of sexual receptivity (estrus) for their reproductive cycles. Horses have a natural breeding season in the spring and the summer. The natural breeding season for horses is the spring and summer. Mares are in estrus for between five to seven days. They experience an inactive period (anestrus) during the winter months.
Charles Love, DVM. Dip ACT. Professor of Equine Theriogenology at Texas A&M University, Charles Love says that normal cyclicity in mares depends on the onset and duration of longer days. The increase in daylight, which is a sign of spring, signals the pituitary gland located at the base the mare’s skull to release what is called follicle stimulating hormone (FSH) into the bloodstream. FSH travels to ovaries where it triggers the formation of a cavity (or follicle) containing an egg (ovum). The hormone estrogen is produced as the follicle develops on an ovary. The hormone estrogen is released when the blood levels reach a certain level. This signals the pituitary to release a second hormone. This hormone, called luteinizing hormone triggers ovulation. The egg is then released from the follicle and sent into the fallopian tube.
After its contents have been released, the follicle creates a temporary structure known as the corpus luteum. It is capable of producing estrogen and progesterone for about 12-14 days. The hormone prostaglandin, which is released from the uterine wall, causes the corpus luteum (which is responsible for conceiving) to be reabsorbed back into the ovary. The estrus cycle is then resumed as the progesterone level drops. However, if the mare does conceive, the progesterone levels drop and the estrus cycle resumes. The corpus luteum is functional, and the progesterone levels remain constant so that the pregnancy can continue.
Dr. Love explained that the mare will be in heat for a few days after ovulating. Then she will lose heat. She may show a variety signs, usually when she is around horses, particularly males, to indicate her willingness to be a stallion. These include lifting her tail and urinating, squatting and “winking”, which is opening and closing her lower vulva, her outside portion, and squatting.
A mare that is ready to breed may exhibit other behaviors than those that indicate she is. However, not all mares will show this behavior. Most common behaviors include tail swishing and kicking, excessive urination, and squealing. A mare may become uncooperative due to pain from a developing foetus, which can lead to reduced performance under saddle.
Dr. Love states that mares can be difficult to heat because of the need to urinate and distractions from other horses. “Some mares may have ovarian pain, and they might actually colic.”
(c) Amy K. Dragoo/AIMMEDIA
A Measure of Control
There are many medications, supplements, and procedures that can be used to suppress or eliminate estrogen. This will ensure that a mare’s behavior and temperament is stable throughout the year, and consistency in performance during training, competition, and in competition. All of these treatments should not be used without consulting a veterinarian who will evaluate the merits and drawbacks of each mare. These are some of the most popular options.
Altrenogest (Regumate) is an FDA-approved synthetic progesterone (synthetic estrogen) that can be prescribed by a veterinarian. The cost for each dose is approximately $23 and can be administered orally, either in feed or directly onto the mare’s tongue with a syringe. It blocks ovulation and increases progesterone levels in the blood. Mares are kept cool as long as it is being administered. Altrenogest can be absorbed easily through the skin, so it is important to take care of it so it doesn’t affect the person giving it. The warning states that you should always use gloves to handle the drug, and to not let it touch skin, eyes or clothing. Altrenogest can cause damage to women’s cycles. Premenopausal women and pregnant women should be cautious when using it.
Medroxyprogesterone Acetate (MPA, Depo Provera) is a synthetic hormone derivative that is used to suppress ovulation. It has not been approved by the FDA for use in horses. A veterinarian can prescribe the drug to reduce mares’ estrus symptoms. Although MPA is not proven to prevent a mare from undergoing heat, studies have shown that injecting the drug can improve a mare’s behavior. (See sidebar “What Role does MPA Play in Competition “). Its long-term effects are unknown.
Anecdotal evidence suggests that dried raspberry leaf can reduce the symptoms of estrus. It can be used as a daily feed supplement. The herbal remedy, which isn’t subject to regulatory scrutiny, has been used for years by women to aid in the maintenance of a healthy pregnancy. It contains antioxidants and nutrients that are believed to relax muscles spasms and improve uterine tone. Although raspberry leaf won’t stop mares from escaping heat, its effects can help with moodiness.
Some mares may experience a suppression of estrus by intrauterine marbles. A veterinarian inserts one sterilized glass marble into the uterus within 24 hours of ovulation. The marble is approximately 35 millimeters (just under an inch) in size, and tricks the body into believing it’s an embryo. This causes the uterine membrane to change its secretion to preserve pregnancy. Although the success rate for intrauterine marble is variable, it is relatively affordable. The cost of the vet’s farm visit and the cost for the marble can add up to several hundred dollars for a implantation that lasts from six months to one year. After the marble has been removed, the mare will resume her normal cycle. It is not recommended to use the marble for more than a year as it can cause complications such as uterine infection or inflammation of the lining. It is possible for pieces or the entire marble to be embedded in the uterine liner. A mare might also expel the marble unnoticed by her owner.
Ovariectomy (spray) is an option for severe ovarian pain that cannot be managed. The mare is under sedation while the ovaries are removed. This procedure is costly and can result in hemorhage or infection. The mare may not be able to conceive permanently, but she could still experience hormone-related behavior problems, as estrogen is made from other sources than the ovaries.
“There have been anecdotal reports that ovariectomy can improve the quality of life.” Dr. Love adds, “Remember that once you remove your ovaries, they cannot be put back.” Owners should be aware that a mare might exhibit heat signs to some degree after ovaries have been removed. This is an unintended consequence.
Dr. Love provides guidance on how to decide the best course of action for a mare that is adversely affected due to estrus. He suggests determining “if the mare performs well in heat.” If the answer is yes, then the problem may be heat-related. However, if the mare doesn’t improve when she is out of season, then you should investigate other causes such as ovarian pain or ulcers, and/or rider inexperience. Frequent urination is another sign of heat in mares. This could be due to stress.
(c) Shannon Brinkman
A Focus on Behavior
John Michael Durr is a professional hunter/jumper rider and eventer who believes that mare management or any other horse requires a deep understanding of the horses. He has worked with many mares, and his own strategy for managing them. He says that the main focus of his approach is to keep a consistent training and managing routine that allows him get to know his mares better so he can quickly identify problems and find the best solution.
John Michael states that keeping mares on a regular routine will help keep them calm and increase the likelihood of you noticing any changes in their behavior or health. I keep an eye out for any signs of [gastrointestinal] problems in competing mares and treat them as necessary. Because they may be more sensitive than a gelding to an uncomfortable saddle, bridle or saddle, I make sure they have the right tack.
John Michael will not give medication to a mare to regulate her cycle unless she exhibits inconsistencies on the ground or under saddle. He gives an example of his experience with Esprit De la Danse (aka Dani), a Canadian Sport Horse mare that he was able to even at the three-star level. When she was in season, she became so attached to her barn friends that she would whine and pace for them rather than eat. She lost weight as a result. She was also constantly distracted which made it difficult for her to follow a consistent training program. OvaMed was prescribed by the mare’s veterinarian after a thorough physical exam. This FDA-approved generic replacement to Regu-Mate helped reduce her stress and attachment issues during estrus.
John Michael says that although she was still sensitive, the medication helped her to be consistent in her behavior. He also created what he calls a “quantifiable system” to help him plan for her unpredictable episodes of fretfulness and how to prevent them from happening again. His approach is to allow mares to have a break from the medications that suppress their cycles. It’s important to me that they have a healthy and regular cycle. They can take the meds off if they feel a little tired from all the events.
John Michael pays attention to the behavior of his horses and does what he feels is necessary to keep them calm. He mentions that he makes sure that the mares have a safe and comfortable place to rest when they travel. This helps reduce stress and increases their ability to cope with the demands of competition. He says that while traveling is difficult for mares, he also notes that while stallions have all the accommodations they need when shipping, the same considerations must be made for mares.
He won’t place a mare next a stallion in a trailer, particularly if she is in season. To reduce attachment drama, he won’t ship a mare to her best friend. He also takes steps to minimize distractions in a mare’s stall by reducing foot traffic and giving her plenty of hay.
A Tale of Two Sisters
Roslyn Johnson is an event horse breeder from Grantville, Georgia. Roslyn has seen firsthand that there is no single solution to managing a mare’s heat cycle. Each mare is unique and should be treated accordingly. As an example, she shares her experiences with two of her homebred mares.
Full sisters Flo (14 years old) and Kite (12 years old) are seven-eighths Thoroughbreds and one-eighth Irish Sports Horses. Both were young horses and started under saddle together as children. They also learned the same training programs. Both have evented to the Intermediate level. Roslyn says that the only difference between their childhoods is how Flo was treated as a foal. Roslyn acknowledges that Flo, the farm’s first homebred mare, was spoiled and “mareish” from the beginning. Roslyn says Kite was raised more disciplined and is “one of the sweetest mares you will ever meet.” She is a hard worker and is consistent.
Roslyn recalls that Kite was always a good sport, even in estrus. But Kite became a problem one day during a competition. At age 7, she began to display cranky and opinionated behavior that was completely uncharacteristic of her. She refused to do what she wanted and was able to get rid of her rider. She was unable to walk and the vets checked her for any lameness.
Roslyn was still worried about Kite’s unusual behavior, even though Kite was correctly pronounced. She trailered Kite to Alabama’s John Thomas Vaughan Large Animal Teaching Hospital. An ultrasound revealed that Kite had an abnormal behavior due to an enormous follicle inside one of her ovaries.
Kite has been receiving Regu-Mate since the episode. She is happy with the results. Flo, her sister, is also on the medication because she is also prone to oversized follicles. Roslyn says that Flo’s behavior is now better.
Roslyn stressed, like medical professionals, that the importance of a thorough veterinary evaluation is essential to determine if mare-ish behavior is caused by estrus. Roslyn also owns an event mare who experienced physical discomfort during her cycles and began to receive Regu-Mate. Unexpectedly, her temper became worse. The treatment was stopped and the mare’s behavior was monitored. After she did not improve, a veterinarian exam revealed that she had a compensatory strain in the back. Her injury was treated and she has not needed hormonal medication since her last cycle.
This episode demonstrates the importance of an objective approach to mare care and estrus. It will help you determine if your mare needs medical intervention during heat or not. This will help you make changes to the way you care for your mare and show that you are concerned about her well-being.
(c) Amy K. Dragoo
What role does competition play?
The debate in the equestrian world is centered on the question of whether or not the main substances used to control mare estrus and in some cases the behavior and breeding of stallions and horses can be used in competition. Altrenogest (MPA) and medroxyprogesterone Acetate (MPA), are used by some owners, riders, and trainers to create a safer environment. This is especially true for stallions that have to deal with potentially dangerous behavior. Others feel the drugs offer a safer alternative to excessive longing to calm horses before an athletic performance. However, competition bans a variety of drugs that can calm horses. What does the major equine sport regulation organizations think about altrenogest or MPA?
The International Equestrian Federation (FEI) bans the use altrenogest in male horses, and MPA in all horses competing in competition. These drugs are not currently regulated by US Equestrian (USEF). The organization did discuss this at its January 2017 annual meeting. The organization discussed this at its annual meeting in January 2017. Altrenogest treated mares did not become heat. However, MPA treated mares showed an increase in luteinizing hormonal, follicles, and ovulated. However, mares treated with MPA also showed an increase in luteinizing hormone and ovulated more than mares that received a placebo. Researchers concluded that MPA has no biological effect on mares’ estrus cycles and that any improvement in behavior must be due to some other effect.
US Equestrian based its findings on the information provided, and concluded that further information was needed before making a decision. The Board of Directors approved the recommendation of its USEF MPA Panel at its 2017 mid-year meeting. This panel will continue to analyze and research the effects of the drug on competition horses. Geoff Teall is the trainer/judge, Elisabeth Goth is USEF Vice President, Laura Graves, Olympian 2016 and Kent Allen, DVM, is the Chair of Veterinary Committee.
A disclosure form, found on the US Equestrian site, must be completed for all horses (mares, mares, and stallions) who receive the medication within three months from the competition start date. This form records the date and dosage of MPA. This data will be used in conjunction with further investigation by the MPA Panel to help us better understand MPA’s effects on competition horses.
Murray Kessler, President of USEF, says that “as promised”, we are studying the use MPA in competition horses. USEF places animal welfare as a top priority, just like our members.
I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!