Reproductive Care For Mares

By Nancy Brannon

As mare owners are planning for next year's foals, Dr. Carla Sommardahl, D.V.M., Clinical Associate Professor-Equine Medicine in the Large Animal Clinical Sciences Department at The University of Tennessee College of Veterinary Medicine provides some important information about breeding and reproductive care for mares.

First, there are some genetic precautions to consider, particularly breeding "lines" and in-line breeding. "Inbreeding in any species is not healthy," said Dr. Sommardahl. "It can be very detrimental to the animal. But in horses, it is not uncommon to breed dams to fathers, cousins to cousins. People are trying to breed for good traits, but along with these they get bad traits. There are not many known genetic diseases in horses and only a few can be tested in the parents prior to breeding. There are other undesirable traits that are inherited, such as, conformation defects, but there is no way to test for them. The foals inherit 50% of their genes from each parent; therefore, the good traits and the bad traits of each parent may be passed on." 

In American Quarter Horses (QH) and horses with QH bloodlines, there are several genetic diseases that available tests can detect: whether an animal has the genetic disease, is a carrier, or is free of the genetic mutation, based on a DNA sample from blood or hair. "HYPP – hyperkalemic periodic paralysis is one of these diseases," Dr. Sommardahl explained. "HYPP is caused by a defect in a muscle sodium channel so that the muscles are hyperexcitable and then become weak. Some horses have tremors; some fall over depending on the severity of the condition. It can affect the heart muscle, resulting in death." Another genetic disease found predominately in the American Quarter Horse is Hereditary Equine Dermal Asthenia (HERDA) which is a disease that affects the skin causing hyperextensible skin, scarring and lesions on the back of affected horses. Polysaccharide Saccharide Storage Myopathy (PSSM) is another inherited disease affecting horses with Quarter Horse bloodlines and is a muscle disease causing signs typical of tying-up. 

"In Arabian horses and Arabian crosses," she said, "the most well known genetic disease is an immunodeficiency in foals called SCID." Severe combined immunodeficiency (SCID) is a genetic condition that results in the death of a significant number of Arabian foals. The condition is inherited as an autosomal recessive trait and was first identified in 1973, and in1997 an estimated 2.5% of Arabian foals died from this condition. Clinical signs show in the development of opportunistic infections, usually of the respiratory tract. Foals with this immunodeficiency inevitably die before five months of age. Cerebellar Abiotrophy is another inherited disease that mainly affects Arabian horses; it causes degeneration of the cerebellum portion of the brain. A genetic test is now available for both of these diseases to determine if your mare or stallion is a carrier or is clear of this genetic mutation. 

Along with these known inherited genetic diseases that can be screened for, there are many family lines and breeds that may be predisposed to other medical conditions. Make sure you know the family medical history of the mare and stallion before choosing the mating and consult your veterinarian.

General health care for mares being bred should include the following.

Reproductive exams

"I recommend a good general physical examination and a general reproductive health check for mares whether they are young or old. This includes rectal palpation and ultrasound of the internal structures of the reproductive tract. It is important to assess the pelvic and vulva conformation of the mare. The mare's conformation can affect her risk of contamination of the vulva, which can lead to infections in the uterus. Any trained veterinarian can do this general reproductive examination along with a general physical examination. If the mare is in good health, then her chances of getting pregnant and carrying the foal to term are good," Sommardahl said.

"The natural breeding season for mares is late April to August, when they start having fertile heat cycles. Mares go through a spring transitional period which is associated with increasing daylight length. Many mares will show normal signs of a heat cycle or estrus during this spring transitional period and may even be receptive to a stallion; therefore, you cannot rely on the behavior of the mare to determine if the heat cycle is fertile. Many people want to breed earlier because they want the foal to be born as close to January first as possible. Most mares will not have fertile heat cycles until late March unless they have been put under lights in the fall or early winter. Horse owners should consult their veterinarians regarding when would be the best time to breed their mares. The veterinarian will be able to determine where she is in her cycle at that point in time. If owners are not concerned about the birth date of the foal, then they should wait until late spring." 

After breeding, the mare will need regular care from the owner and veterinarian. "Have the veterinarian do a pregnancy exam on the mare 15-18 days after she has been bred. That is the earliest time that the fetus can be detected. It is also important to check for twins and this is the safest time to do something about that situation if she does have twins. Mares are not made to carry twins and usually both will be aborted later in the pregnancy. The sooner twins are detected, the easier it is on the mare," Sommardahl said. 

"After the first pregnancy check at 15-18 days, then another should be done at 30 days. The first trimester is very important, just as it is in humans. It is during this first trimester that the mare is most likely to abort or reabsorb the fetus. This is usually a result of something wrong with the fetus or just one of those things that occurs. If a mare continually loses foals during the first trimester, then the veterinarian should examine the mare for hormonal problems or an infection in the uterus.

"After this point, we usually don't need to check the mares again until fall unless the mare has a history of problems during pregnancy. If this is the case, then she will need regular pregnancy checks, especially with middle-aged or older mares who are more at risk of carrying the foal to term. We will also check mares if the develop a vaginal discharge or have any other health problems that may affect the pregnancy. Mares don't require regular pregnancy checks or fetal examinations like humans. Although it would be nice to evaluate the foal's development, the ultrasound machines available today are not designed for this type of examination and do not allow deep enough visualization of the entire fetus in most mares," Sommardahl said.

Feeding and nutrition

"For general care, the mare does not need anything special regarding her feed, nutrition, or environment in the first 5-6 months. In the last five months (pregnancies last 11 months), she may need more nutrition-wise, more calories and protein. But don't over feed the mare; the feeding regimen depends on the condition of the mare. In the first 5-6 months, feed what she needs for her body type and work load. Keep her in good condition, but, again I emphasize, don't over feed her. The owner's veterinarian can help with guidelines on feed and nutrition.

"Good quality pastures and grass hay should be the basis of the diet. Choose a reputable feed and feeds that are made for horses. Many companies, such as Purina, do a lot of research to improve their feeds and the quality of nutrition for horses. Nutrena and Triple Crown are also good, as are most Co-Op feeds. If the feed is safe for a cow, it may not necessarily be safe for a horse," she explained. Cattle and horses have vastly different digestive systems. "Look for consistency in feed, that every bag of feed has the same nutrient content. There are a lot of herbal supplements and 'remedies' on the market that can be problematic. If you use them, make sure they are tested and safe for pregnant mares."


"Prior to breeding the mare should be up-to-date on all her vaccinations. Then during pregnancy, the vaccine recommended is equine herpes virus, which causes abortions if contracted during pregnancy. This should be given as a killed vaccine starting at 3 months and then repeated at 5, 7, and 9 months of pregnancy. Then, 4-6 weeks prior to foaling, we recommend a booster of all vaccines that are safe for pregnant mares. There is a 4-way shot which includes tetanus, influenza, eastern and western equine encephalitis (WEE, EEE). Other combination vaccines may include the West Nile virus and herpes virus. It is important to make sure that the vaccines used are safe for pregnant mares. Vaccinating at this time will help insure that adequate levels of antibodies against these diseases will be present in the colostrum or first milk of the mare."


"Mares should have access to good shelter and good quality drinking water at all times. There should be no new stresses in their environment. There is no right or wrong way to keep mares, either in stalls or out in the pasture. Maintain the environment that she's used to, while making sure she has access to shelter and shade in the hot summer months and/or colder months. Observe her regularly, and check her daily during the last trimester for any visible problems. Check her general attitude and appetite, looking for normality. As time gets closer to her due date, gestation is an average 340 days, observe her more regularly and begin preparing a place for her to foal."


"Two weeks prior to foaling, prepare a place for the mare to foal. It can be a stall, a small paddock, or any place away from other animals. Watch her more closely, especially if this is her first time or you don't know her patterns. Mares are usually consistent in their foaling patterns. Mares deliver rather quickly, too. Once you see labor has begun, the foal should be out within 30-45 minutes. The onset of labor is usually the time their water breaks or you notice contractions. Once the water breaks, the clock starts ticking. Most mares don't have problems foaling, but if you don't see active progress, call your veterinarian immediately. 

"If you see something coming out besides the foal, call the veterinarian. The foal should come first, not the placenta. If the opposite happens, this is abnormal. If this is your first time, then you may want to have an agreement with your veterinarian to call him/her once you see foaling has started. That way, when the veterinarian arrives, he/she can help with any problems in the mare and give the newborn foal a check-up. 

"We recommend a routine foal check-up at 24 hours after birth to make sure the foal is healthy and has ingested adequate colostrums by measuring its antibody levels in the blood. Owners may put chlorahexadine solution (Nolvasan®) or 2% betadine solution on the navel or umbilical stump to disinfect the area. Be sure not to use tincture of iodine; this will burn the area. Don't cut the umbilical cord once the foal is born; it will break on its own. However, if it is wrapped around the neck or causing an immediate problem, then it should be torn rather than cut to prevent excess bleeding. The foal should stand and nurse within 2-4 hours after birth. If the foal is not standing within this time, and seems weak or sick, call the veterinarian.

"Mares should pass the placenta within 2-3 hours after foaling. If it doesn't pass, it can cause serious problems in mares. Save it in a plastic bag for the veterinarian to check to be sure that the entire placenta was passed when he comes to check the foal," Sommardahl said.

Common problems

Avoid fescue hay or pasture for pregnant mares. "Check with your extension agent or someone knowledgeable about grass content in hays so you know if the hay you are feeding contains fescue. If you do have hay or pasture containing fescue, the mare is probably going to be OK on that in the first 4-6 months of pregnancy. But in the last part of her pregnancy, the mare should have fescue-free hay and pasture.

"The problem is a fungus that infects fescue grass during growth and remains in the hay." The fungus is Acremonium coenophialum, an endophytic fungus present in tall fescue grass and seed. "It is hard to find fungus-free hay or pasture because the fungus travels by air and can infect a whole field that may have once been fungus-free. It is hard to control because heat and humidity are ideal growth conditions for it. 

"Even with all the information there is available about feeding fescue to pregnant mares, it is still a problem. Every year we see mares without milk or foals with dysmaturity. Dysmature foals are carried to term, but have immature characteristics. This is related to placentitis, which causes placental thickening. When this occurs, the foal does not get enough nutrients from the mare because the placenta is too thick."

Read informational articles about mares and foaling in reputable publications. "The web site," the web site of the American Association of Equine Practitioners, "has some excellent information. But there is also a lot of misinformation, too, especially on the web. Beware of opinions; make sure the article has time-tested research information and the advice is not just a fad. Always question what you read, get a second opinion – ask your veterinarian." 

The UT College of Veterinary Medicine Continuing Education offers educational seminars for horse owners. The next Horse Owners Seminar will be held on March 12, 2011. For more information, contact Barbara Campbell, UTCVM Meeting Manager

"Preparing your mare for breeding," a PowerPoint presentation by Dr. John Henton, Past Director of Continuing Education, can be downloaded at:

For information about Large Animal Clinical Sciences Department at UT College of Veterinary Medicine visit:

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