NewsHow long is a horse pregnant? The quick answer is between 10 and 12 months, or around 326 and 354 days (although there have been cases where gestation for a mare has gone as long as 365 to 370 days). The majority of mares only give birth to one foal each pregnancy, while twins may sometimes happen. But if you’re thinking of breeding your horse, there’s a lot more to know.
Mares are seasonally polyestrous. In plain English, this indicates that the mare behaves somewhat similarly to a cat in that she goes through many cycles at the same time. Mares cycle at times of prolonged sunshine, much like cats. This is supposed to be an evolutionary adaptation that guarantees the mare will give birth in the spring, when conditions are most favourable. Given these factors, a mare can only have one pregnancy a year and will usually only have one foal in a given year.
The Mare’s Cycle is Key
In order to manage mares well in general and to arrange a successful breeding, it is essential to understand the mare’s cycle. Mares are light sensitive because they are seasonally polyestrous. This implies that when the amount of sunshine increases, her cycles will begin by becoming less melatonin-dependent.
Important dates for horse breeders to keep in mind are:
- June 21 marks the Summer Solstice, the year’s longest day and the height of the natural mating season.
- On September 21, there will be an equal amount of light and dark, and the mares will start shutting off as fall approaches.
- December 21 marks the Winter Solstice, the shortest day of the year, when mares are in their darkest anestrus.
- March 21 marks the Spring Equinox, a day of equal light and darkness, and mares are in the Spring Transition stage.
These dates are, of course, approximate. As the commencement of cyclicity is likely mediated in part by a neurotransmitter also involved in prolactin release, temperature may potentially affect this. The gonadal axis’ opioid inhibition may also be lessened, which is considered to contribute to how the breeding season begins. Around the Summer Solstice, which is also the animal’s natural mating season, normal horse cycles begin.
The duration of the mare’s gestation cycle may also be impacted by seasonal factors. Early-breeding mares (often during the first quarter) sometimes carry their fetus a little bit longer than anticipated. Mares that breed later in the year—during the longer days of spring and summer—might have shorter gestation periods. 2 A mare’s gestation duration may also be affected by other variables, such as whether the foal is a colt or a filly. Colts may have gestation periods that are two to seven days longer than those of fillies. Additionally, body weight affects gestational length; smaller mares often bear their babies for a longer period of time than heavier mares.
When the longer days of spring and summer arrive, some breeders of performance horses may periodically alter a mare’s reproductive cycle by exposing her to artificial light. This causes the mare to go into heat earlier, which allows the foal to be born earlier in the year, often an advantage for the owners and managers of performance breeds.
Gestation Stages
Mares experience three trimesters of pregnancy. Conception marks the start of the first trimester, which is typically over by two weeks. 3 It is crucial to have the mare’s health and the health of her foal checked by the vet throughout the first trimester.
The veterinarian may use an ultrasound to establish the foal’s viability and find the foal’s heartbeat at around 25 days. If it is one of those really uncommon cases, twins may also be verified at this point. If twins are discovered, the veterinarian could inquire as to whether the owner or management wants the second embryo removed to improve the chances of the remaining one surviving. Twins may occasionally be aborted by mares during the first six weeks of pregnancy, which would clearly make the pregnancy unviable and result in the loss of both foals. Upon ultrasound screening at three months, the foal starts to resemble a horse; distinctive traits may be seen, and the gender of the foal can be identified. 3
Around day 114.3, the second trimester starts. The mare may start getting shots and a dewormer at this time. In order to provide the rapidly developing foal the nourishment it needs, the mare’s diet should be boosted. By six months, the mare will begin to show.
At Day 226, the mare is in her third trimester. The frequency of the vet appointments need to be increased at this point. Up to the seventh month, you may keep up with your regular workout. Maintaining the mare in a relaxed and stress-free environment as she approaches giving birth is crucial. Major changes should be avoided since they may make the mare uneasy.
Leading Up to Foaling
On average, the day of conception should occur between days 326 and 354. Some breeders utilize test kits to assist predict the day of foaling, which may be helpful, particularly if it’s the mare’s first foal and the mare’s foaling procedure is unknown. 2 The mare is likely to exhibit signals that her body is preparing to give birth in the days leading up to delivery. Her udder can seem full and start to drop milk. As the foal gets ready to emerge, her tummy will seem lower than in previous weeks.
For the mare’s comfort, a large stall with plenty of straw, fresh water, and hay should be supplied. The mare will probably paw the ground and become restless as she starts to give birth. While giving delivery while lying down, she may sometimes go up and down. 2,3 The amniotic sac and then the head and legs will likely be the first parts to become apparent. The horse usually gives birth a few minutes after the amniotic sac becomes apparent. 3
Labor and Delivery
More than 85% of mares give birth at night, which is likely a survival strategy that enables the foal to be prepared to gallop alongside the mother once daybreak approaches. The mare will be tense throughout the early stages of labor. She could kick at her stomach and start nesting. During foaling, mares often perspire; this is known as the mare “heating up.” Wrap the tail and clean the perineum. This phase often lasts for an hour.
Typically, the second stage of labor lasts between 15 and 25 minutes. The foal’s front hooves, nose, ears, and other features should gradually become visible. 2 The research strongly advises that it should be established that the foal is breathing, even if the wise horse owner or breeder will have a veterinarian there. This may be induced by gently massaging the foal’s nostrils with a blunt item. If necessary, aggressively rub the foal with a cloth. 3 
Photo Credit: Equine-Reproduction.com, LLC
Iodine should be used to disinfect any biologics, among other advice and cautions. 2 It is suggested against cutting the foal’s umbilical chord right away after birth, as is done with humans. Some scientists think that after delivery, a certain quantity of blood enters the foal via the umbilical artery.
The foal was delivered during the third stage of labor. According to the literature, if the placenta is not delivered after three hours, it should be treated as an emergency and seen by a veterinarian. The foal should be able to stand within an hour and show signs of being able to breastfeed within two. The mare herself should usually require no post-partum care.
Emergency Situations
The amniotic sac becoming red during the second stage of labor is one of the most frequent foaling crises. The amnion (also known as the amniotic sac), a white membrane enclosing the foal, is the first to emerge during a typical foaling. In a few rare cases when the placenta has prematurely disengaged from the uterine wall, the amnion will include blood, giving it a deep crimson look. The foal’s death is a possibility in this extreme circumstance. 4 With “breech births” (as opposed to the typical caudal presentation), additional potential issues may develop, although an experienced horse veterinarian should be able to manage any of the aforementioned issues or any unanticipated situations with reasonable ease.
1Eilts, B. Equine Seasonal Cyclicity. In: therio.vetmed.lsu.edu Aug 2010.
Karen S. Johnson 2. How long do mares stay pregnant? Mom.me, 21 November 2017, accessed 7 October 2018. Animals www.animals.mom.me/long-female-horses-pregnant-10…
3 Expectant Mare: Ensuring the Pregnant Mare’s Health and Well-Being. American Association of Equine Practitioners, 7 Oct. 2018. www.aaep.org/horsehealth/expectant-mare-assuring-…
4 www.ogec.com.au .
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