Animal Care

Pregnancy in Horses

Horses are mammals, and like all mammals, give birth to live offspring who are nourished for the first part of their life by their mother’s milk. A mare (a female horse) can only produce one foal per year. A mare is capable of producing a foal at about 18 months of age, but it is healthier for mare and foal if the mare is at least four years old, as, by this time, the mare has reached her full size. A mare may continue having foals until she is in her late twenties. A stallion (a male horse) may continue breeding mares into his twenties as well, although the quality of his sperm may decline as he ages.

Foals can stand about 30 minutes after birth. They may nibble grass, concentrate, or hay within a few days after birth, although their mother’s milk will be the main source of nutrition. They may be weaned from their mothers as early as three months after birth, although many breeders choose to leave mares and foals together longer. Although feral horses mate and give birth without the attention of a veterinarian, many problems can be circumvented by having the stallion checked before breeding, and mare checked and cared for properly during the gestation period.

Average Gestation Period

The gestation period in horses is typically between 330 and 345 days, or 11 months. Some mares will be inclined to foal earlier or later than the average, and breeders will get to know these tendencies. Ponies usually have a shorter gestation period than horses. In a natural environment, the stallion will breed the mare in the summer, and foals will be born the next year, in spring and early summer. This ensures that the foals are born when pasture is abundant and the weather is mild.

Mares are considered seasonally polyestrus, which means they go into heat (estrus) and are receptive to a stallion at regular periods during the spring and summer. These seasonal estrus cycles are approximately every three weeks. However, breeders who wish to manipulate the breeding cycle, so foals are born earlier in the year (commonly done in the Thoroughbred racehorse industry) will use artificial lighting to simulate the longer days of spring and summer. The artificial daylight stimulates the mare’s brain to produce the reproductive hormones needed to induce estrus. This allows mares to be bred earlier and in turn have a foal earlier the following year.

Checking For Pregnancy

Beyond the absence of an estrus cycle, mares may not show any visible signs of pregnancy for the first three months. Pregnancy can be confirmed by ultrasound after approximately two weeks after the breeding took place.4 Blood and urine testing can be done two to three months after conception. Alternatively, a veterinarian may be able to manually feel the small embryo in the mare’s uterus approximately six weeks into the pregnancy via rectal palpation.

It’s important to have the mare checked by a veterinarian early in the pregnancy for her health and the health of her foal. Horse twins are rare but can lead to the mare aborting. If the twin foals are carried to term, there is a possibility of losing both. For this reason, it’s often recommended to “pinch-off” one embryo. This is done very early in pregnancy. It’s not unusual for a mare to lose a pregnancy, so it’s recommended to ultrasound, blood, or urine test again after about three months. Things like checking how a mare shakes her head, the look in her eyes, or which way a needle moves when held over her belly are not accurate methods of determining if she is in foal.

Later Stages of Gestation

After about three months the foal will be developing rapidly and start to look like a small horse. After about six months, the mare may start to be visibly pregnant. Mares that have foaled before may show an expanding belly sooner than a maiden mare. Over the remaining months, the mare’s belly will continue to grow as the foal approaches its foaling date. About two weeks before the due date, the mare’s udder will start to expand and start producing sticky yellowish fluid.

After about 315 days of pregnancy, an owner should watch the mare closely for impending signs of foaling. For example, the yellowish fluid will turn into the first milk or colostrum. The udder may drip, and the muscles around her tail head will become more relaxed. Her belly may appear to drop, as the foal positions for birth. At this point, birth is imminent, and the mare must be checked frequently for signs of foaling. Shortly before birth the mare will appear restless, may paw the ground, and check her sides (similar to colic symptoms). She should be stalled in a large, clean stall, preferably ​bedded with straw. The mare may lie down and get up repeatedly but will give birth lying down. First, the amniotic sac may be visible, and then the foal’s front hooves and nose. The foal is normally birthed within a few minutes at this stage.

What Causes Colic?

Horses can have colic for innumerable reasons and even with veterinarian care, the cause can go undiscovered. It’s important to remember that colic is a symptom, not a disease in itself. So because it is a symptom of another problem, there is no one sure-fire treatment that will alleviate all colics. Some colics might be just a “tummy ache” from a change in the weather or a mental upset. Or, colic symptoms may indicate a far more serious, even life-threatening problem.

Common Causes of Colic

The distress that a horse is in while it colics indicates that something is going wrong with the digestive system. Here are some common reasons your horse may be exhibiting colic symptoms.

  • Changes in feed
  • An accumulation of sand in the caecum is called sand colic
  • Ingesting fungus from moldy hay
  • Ingesting foreign objects can all trigger colic symptoms.
  • Some owners claim nervous horses can experience a change in management
  • Senior horses in response to rapid air pressure changes may develop spasmodic colic. (No conclusive clinical information supports this claim).

Impaction Colic

Impaction colic can happen more commonly during the winter months when horses or ponies are fed hay and have only frigid water to drink. But if a horse is chronically dehydrated, this type of colic can happen at any time. The combination of dry feed and dehydration can be disastrous. Because the horses don’t drink enough water the food forms an obstruction in the intestine. A horse that eats its bedding or accidentally gorges on grain can suffer from impaction colic. (Overeating grain or fruit can also cause laminitis or founder.)

Parasite Damage

Parasite damage or load can cause a horse to exhibit colic symptoms. The parasites irritate the intestinal tract as they cause damage. Horses with a parasite load, or who have just been dewormed because they have a heavy parasite load may colic. Parasites can also cause damage to the intestines that can lead to ongoing problems. This is why it is so important to keep internal parasites in check with an effective, regular deworming program.

Kidney stones may also cause colic symptoms. Anything that goes awry with the internal organs may make the horse appear colicky.

Cold Water

Colic can be caused by too much food eaten too quickly, or drinking a large amount of cold water. Especially if the horse has EGUS, it may be colicky after eating or drinking a large amount. When the weather is cold, keep your horse’s water above frigid temperatures with a heated bucket, a trough heater, or by carrying out hot water to mix with the cold. This will prevent a cold shock to its belly. And, if your horse drinks more in the winter, it’s less likely to suffer impaction colic.

Intestinal Twists

Twisted intestines and telescoped sections of intestines occur and the cause is unclear. Some people believe it happens when a horse rolls, it can cause a loop of intestine to loop, telescope, or twist. Some feel it’s more likely to happen with big barreled horses or mares who have had several foals. Fatty deposits on the intestines can cause them to flip or twist. Some horses have had multiple surgeries to correct twists. It’s not known the exact reason this happens.

Nursing Foals

Foals live on their mother’s milk for the first weeks of its life. The first milk it receives shortly after birth contains important immune-building qualities. By the time a foal is about two months old, it will need to eat grass and is often fed special concentrates made for foals, because its mother’s milk will no longer supply enough nutrition to support its rapid growth.

Domestic horses are usually weaned early, at about three to six months, while feral horses may wean much later. Mares are often bred shortly after they give birth, so in early pregnancy, are nursing a rapidly growing foal. Occasionally, a mature horse will still try to nurse, and be very attached to its mother, but this is largely due to poor management by its owners, rather than any need on the horse’s part.


Foals may be weaned at any time between three months and a year. Once weaned, the foal may be referred to as a weanling. During this time, they continue to grow rapidly. While it’s best to start handling a foal from birth, training in hand can begin and it’s necessary to teach a weanling ground manners. They will not be ready to ride until they are more mature. Some people start as early as two years, while most prefer to wait until the horse is about four years of age.

Usually, the term foal is used to refer to a very young horse, but you’ll sometimes hear an adult horse referred to as another horse’s, either it’s sire or dam’s foal. The word colt is sometimes used to refer to a baby horse, but this is incorrect as a colt is always a male foal.


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