NewsHow long do horses give birth? Well, the short answer is 10 to 12 months, or from approximately 326 days to 354 days (although there have been cases where gestation for a mare has gone as long as 365 to 370 days). Most mares only carry one foal per pregnancy, although twins do occur on rare occasions. But if you’re thinking of breeding your horse, there’s a lot more to know.
Mares are ovulatory year-round. To put this in lay terms, it means that the mare is something like a cat in that she will experience several cycles during a particular season. 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 circumstances, a mare can conceive just once a year and typically gives birth to only one foal each 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.
Naturally, these dates are a rough estimate. Temperature can also influence the onset of cyclicity as this is likely to be regulated in part by a neurotransmitter also involved in prolactin secretion. 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.
Some breeders of performance horses occasionally manipulate a mare’s breeding cycle, using artificial light to stimulate the longer days of Spring and Summer. This results in the mare going into heat sooner, which permits the foal to be born earlier in the year, which is often advantageous for performance breed owners and managers.
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. At three months, the foal begins to look like a horse upon ultrasound examination; key features can be detected, and the gender of the foal can be determined. 3
Around day 114.3, the second trimester starts. During this time, the mare can begin to receive a dewormer and vaccinations. The mare’s feed should be increased to provide the needed nutrition to the fast-growing foal. The mare’s first showings will happen at six months.
The mare is in her third trimester as of Day 226. 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. As the mare nears giving birth, it is important to keep her in a comfortable and stress-free environment, avoiding any major changes which might cause the mare to be anxious.
Leading Up to Foaling
On average, the day of conception should occur between days 326 and 354. There are test kits some breeders use to help anticipate foaling day, which can be useful especially if it’s the mare’s first foal, the mare’s foaling process 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.
The mare should be provided with a large stall with a lot of straw, fresh water and hay for her comfort. 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
Most mares (greater than 85%) foal at night, which is probably a survival adaptation that allows the foal to be ready to run with the mare once daylight arrives. 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 Although the prudent horse owner or breeder will have a veterinarian in attendance, the literature strongly suggests that it should be determined that the foal is breathing. 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. The literature indicates that if the placenta is not passed within three hours it should be considered an emergency requiring a veterinarian’s attention. Within one hour, the foal should be standing, and should demonstrate the ability to nurse within two hours. Typically, the mare herself shouldn’t need any 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 Other potential problems can arise with “breech deliveries” (versus the normal caudal presentation), but the seasoned equine veterinarian should be able to handle any of the above or other unforeseen circumstances with relative 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…
3Expectant Mare: Assuring the Health and Well-Being of the Pregnant Mare. 7 October 2018. American Association of Equine Practitioners. www.aaep.org/horsehealth/expectant-mare-assuring-…
4 www.ogec.com.au .
About NexGen Pharmaceuticals
The nation’s top veterinary compounding pharmacy, NexGen Pharmaceuticals, provides both sterile and non-sterile compounding services. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
In order to provide better veterinary patient care, our pharmacists are also urged to establish close working ties with our veterinarians. Such relationships foster an ever-increasing knowledge base upon which pharmacists and veterinarians can draw, making both significantly more effective in their professional roles.
Disclaimer
This blog post’s material is generic in nature and is meant to serve as a reference guide. It does not cover all possible uses, actions, precautions, side effects, or interactions of the medications shown, nor is the information intended as medical advice or diagnosis for individual health problems or for making an evaluation as to the risks and benefits of using a particular medication. If you have any health issues, you should visit your veterinarian for diagnosis and treatment. The Food and Drug Administration (“FDA”) has not reviewed the information or representations and has not given its approval for the drugs to be used in the treatment, diagnosis, or prevention of illness. NexGen Pharmaceuticals prepares custom medications under the guidance of a veterinarian. The veterinary medications made by NexGen Pharmaceuticals are not meant to be administered to animals raised for human consumption.
Regarding the effectiveness, appropriateness, or suitability of any particular dosing, products, procedures, treatments, services, opinions, veterinary care providers, or other information that may be contained in this blog post, NexGen Pharmaceuticals, LLC makes no recommendations, endorses, or claims. NEXGEN PHARMACEUTICALS, LLC IS NOT RESPONSIBLE NOR LIABLE FOR ANY ADVICE, COURSE OF TREATMENT, DIAGNOSIS OR ANY OTHER INFORMATION, SERVICES OR PRODUCTS THAT YOU OBTAIN THROUGH THIS BLOG POST.
