Pregnancy in Horses: Stages, Duration, and Challenges

At the sight of a mare with her newborn foal, every rider's heart beats faster.
For the mare to give birth to a healthy foal, it must be optimally cared for during pregnancy and accompanied in the best possible way. But there are a few things to keep in mind here! Feeding, husbandry, and exercise play a special role. All important information and answers can be found here!

How Long Is a Mare Pregnant?

Horses have a relatively long gestation period. On average, a mare is pregnant for 11 months, although the exact time depends on the breed, age, and health of the mare. Usually, the gestation period varies between 320 and 355 days. The pregnancy proceeds in three phases, during which the embryo develops into a foal. 

The first phase of pregnancy 

Since the egg cell of a mare is capable of fertilization for about 8 hours and a maximum of 12 hours, an artificial insemination or a mating act in a natural way, a "natural jump" is necessary for a pregnancy during this period. Once this has occurred, the fertilized egg travels through the fallopian tube to the uterus in 5 to 6 days and attaches to the uterine lining from day 16. 

An ultrasound examination from day 15 or a rectal examination from day 18 can confirm pregnancy. In addition, after 18 days, a veterinarian can detect the fruiting sac, which has now grown to about the size of a chicken egg. After about six weeks, the fruit sac has grown to the size of a fist, and by the third month, it is as large as a loaf of bread. 

Especially in the first 30 days, the embryo may be rejected. For this reason, a second ultrasound examination should be performed two to three months after insemination. 

The middle phase of pregnancy 

If no problems were found during the ultrasound examinations already performed and the mare maintains her good health, the embryo can continue to develop. From the fourth month, the so-called "ball stage" is reached and the first movements of the fruit can be observed. The period between the fifth and eighth month is called the "descent stage", as the uterus descends below the abdominal viscera. 

The last phase of pregnancy

In the last months of pregnancy, the foal is in the growth stage. Now the foal grows to its full size and turns around its longitudinal axis. The foal's head rests between its front legs, which now point toward the birth canal.

Recognize Pregnancy in the Horse

The external signs of pregnancy in the horse are not visible in the first few months. Only the lowering of the uterus in the descent stage and the growing abdominal girth in the growth phase make a pregnancy clear. Nevertheless, nowadays various methods are available for the early detection of pregnancy. 

An ultrasound examination is possible from the 15th day and is usually performed between the 18th and 21st day. This examination should be repeated after 60th to 90th days. In addition, a rectal examination is possible from the 18th day. In addition, a determination of progesterone can be made by a blood test between the 18th and 40th day. The most reliable method for pregnancy diagnosis is the determination of PSMG between the 04th and 100th day by blood examination. Last but not least, a urine test can be done from the 120th day, in which estrogen should be detected.  

Twin Pregnancy and Problems with Pregnancy

In each pregnancy of the mare, two eggs develop in the uterus during the first stage of gestation. In about 95% of pregnancies, one of the embryos is resorbed between the 7th and 11th day. This can be checked with the help of an ultrasound by the attending veterinarian. If one of the embryos is not resorbed and both fertilized eggs continue to develop, a decision must be made with the veterinarian about the further course of the pregnancy. In addition to medical intervention by the veterinarian to eliminate one embryo, abortion may occur at a later time. 

The reason for this is that the mare can only form one placenta during pregnancy and this fills the entire inner surface of the uterus. Consequently, the mare has no room for two placentas and the twin foals must share one. If this is not the case, the twin foals are usually smaller at birth, weaker, more susceptible to disease, and have a lower chance of survival. Consequently, twins are rarely carried to term. 

In each of the stages of gestation, disorders, and termination of gestation may occur. If a disturbance occurs within the first three months, it is referred to as early resorption. Here, the fruit dissolves and is broken down through the bloodstream. If abortion occurs after the third month, this is called abortion of the fruit. In this case, the fruit, which has not yet fully matured and is not viable, is rejected. 

Abortion occurs when the pregnancy is terminated and the fetus is not viable outside the uterus. Abortion can be triggered by infectious causes, such as viruses, bacteria, fungi, or parasites, as well as non-infectious causes, such as twisting of the umbilical cord, malnutrition, changes in the endometrium, impaired placental function, or stress. 

Feeding During Pregnancy

In order for a healthy and strong foal to be born, the mare's attitude and feeding during pregnancy are particularly important. Already before the mating, the current health condition, as well as the weight of the mare, should be checked to avoid complications during the pregnancy. 

After confirmation of good health and pregnancy by the veterinarian, there is no need to immediately change the feed. Until the seventh month of pregnancy, the mare can be fed her "normal" feed.

In the last phase of pregnancy, the mare's energy requirements increase sharply, as the growth phase of the fetus now begins. For the foal to grow in the best possible way, the amount of feed must be adjusted and supplemented with the necessary minerals and nutrients. Especially during this time, the mare needs more protein, vitamin A, calcium, phosphorus, zinc, selenium, and copper. Here it is recommended to add a supplementary feed specifically tailored to the needs of the mare. 

In addition to adjusting the amount of feed and the contents of the supplementary feed, which benefits the health of the mare and the care of the foal, some feeds should be avoided, as this can lead to premature abortion in the worst case. In general, frozen as well as contaminated feed should be avoided and attention should be paid to mold in hay and straw. Haylage and silage should not be fed during pregnancy due to increased bacteria levels. Caution should also be exercised when feeding forage with an elevated iodine content. An over-supply of iodine can lead to goiter and malformation of the limbs. 

Riding During Pregnancy

Particularly pregnant mares need sufficient exercise to stay healthy and fit, in addition to proper feeding and regular check-ups by the veterinarian. A complete cessation of activities and a lot of rest in the stable are not part of the natural needs of a pregnant mare. Varied and regular exercise supports the development of condition, muscles, and a healthy metabolism and promotes a birth process that is as free of complications as possible and serves as preparation for the time after birth. In addition to the health benefits for the mare, sufficient exercise also ensures healthy physical development of the foal in the womb.

The daily routine of a mare does not have to be completely changed during pregnancy. Up to the 8th month of pregnancy, a pregnant mare can be ridden "normally". Prerequisites for riding during pregnancy are that it is not a high-risk pregnancy or that there are no other health complications in the mare. In addition, care should be taken not to physically overload the mare and to avoid stressful situations. This is especially important to keep in mind during the first 30 days of pregnancy to avoid termination of the pregnancy. 

A varied exercise program is absolutely essential for a pregnant mare and can be varied to suit her needs.

While jumps and complex dressage exercises should rather be avoided, a relaxed training in all basic gaits or a relaxed cross-country ride is highly recommended. In addition, the use of a walker and work on the lunge line can be integrated into the training plan and support muscle and condition development. For mental variety, skill exercises and ground work are suitable.  

The mare's girth changes especially in the last third of pregnancy, as the foal takes on its maximum size. In the last four weeks before birth, riding as well as lunging should be completely stopped. Regular grazing with conspecifics and walks in hand or as a hand-horse replace riding and still provide a varied occupation and serve as optimal preparation for birth. In addition to the exercise program, continuous contact with the caregiver through extensive grooming sessions of the mare is important. 

Preparation of the Foaling Box

A foaling box is a special horse box that is spatially separated from the other boxes in a stable and that is used by the mare during pregnancy and birth. The foaling box must provide the safest and quietest possible retreat for the mare to create a stress-free environment and allow for a birth that is as free of complications as possible. This principle is based on observations of pregnant mares in the wild leaving their herd before giving birth. The purpose of the foaling box is to create the most natural environment possible and to allow the mare's natural drive "of being alone" during birth.

A suitable foaling box should have about 14 to 20 square meters and have enough room to move so that helpers or the vet can easily support the mare during birth. An appropriately large box also prevents the risk of the mare getting stuck. In addition to size, there are other factors to consider in preparation. The box must have sufficient brightness and fresh air, as well as be dry and easy to clean. The lighting of the box and the stable area should be sufficient to ensure safe monitoring at night. A complementary measure is to equip the box with a video camera and a birth notification system (harness, halter, chip). These digital monitoring options notify the recipient via smartphone when the mare is having problems or preparing for birth and allow 24/7 monitoring.

To ensure the mare can comfortably adjust to her new "living situation" and prepare for the arrival of her foal, it's best to move her to the foaling box six weeks before her due date. This allows for a calm and stress-free transition and gives the mare time to build up antibodies that will be passed on to the foal through her colostrum, which is crucial for the foal's health.

Signs of the Pending Foal Birth

After the mare has been placed in her foaling box, it is really important to pay attention to the physical signs of impending birth. Since the average gestation period of a mare is between 320 and 360 days, it is difficult to accurately time the foaling date. 

The first changes before the onset of parturition are the formation of edema on the lower abdomen, in the udder area, and on the hind limbs. In addition to a swollen vulva and a significantly wider pubic cleft, resin drops form on the udder. Shortly before birth, small amounts of mucus flow out and in many mares, milk flow begins with the onset of labor. 

In addition to the physical changes, other signs of impending birth include restless pacing, restlessness, and nervousness, as well as pawing and twisting of the neck toward the abdomen. If this is followed by lifting of the tail for minutes at a time, profuse sweating, defecation, and constant standing up and lying down, then labor has begun and it won't be long before birth. Now the mare needs a lot of rest regular checks and close observation. A foal birth takes an average of 30 minutes, some mares also need up to 60 minutes.