Horse pregnancy is a pretty fantastic process that is both exciting and nerve-wracking for horse owners!
I’ve been through the process myself, and my nerves were shot!
If you want to breed your foal, it is not a decision to take lightly, and it is essential to learn as much about equine pregnancy and breeding as possible.
To help you get started, I put together this horse pregnancy stages introductory guide.
READ MORE: How Many Horse Breeds Are There?
How Can You Tell If a Horse is Pregnant
During the first months, when a mare is pregnant is pretty much impossible to tell if she is pregnant by just looking at her. In fact, this can be the situation for several months.
The earliest sign that might make a horse owner look at further tests is if the mare no longer comes into season (estrus).
However, some mares do not show they are in season though this can make it trickier.
If you purposely breed your horse, the standard way to check if a mare is in foal is by doing a transrectal ultrasound. The earliest the ultrasound can detect an embryo is 9-10 days. 
Here’s a cool video on how ultrasound is done on a horse.
@wildirisfarm Ultrasound to see if Stormy is pregnant #horse #fypシ #horses ♬ original sound – Wildirisfarm
However, it is better to wait until day 16.  This is an important time to check mare pregnancy because you must check for twins and deal with the situation before the embryo becomes fixed in the uterus.
While twin foals are adorable, those that survive birth are rare. It is dangerous, even life-threatening, to both the mare and the colt. To put it bluntly, you never want your mare to carry twins.
While twin foals are adorable, those that survive birth are rare.
It is dangerous, even life-threatening, to both the mare and the colt.
To put it bluntly, you never want your mare to carry twins.
Another popular way to tell if a horse is pregnant is to use a blood test. This method is not always accurate but is more reliable once the pregnancy reaches 35 days and up to 100 days.
This test looks at equine chorionic gonadotropin (ECG), which stays elevated in the 35 to 100-day range. 
If you do this test on a mare that is much further along in her pregnancy, such as at over 200 days, it will show no rise in ECG levels and give you a negative result.
The second type of blood test looks at the level of estrogens. However, if this test is done before 80 days gestation, it will likely give you a false negative.
Palpation is the third way a vet can check for horse pregnancy.  A good vet will check the uterine tone and check the cervix is elongated and closed.
READ MORE: Can Horses Live Alone?
Stages of Horse Pregnancy (With Pictures)
There are several equine gestation stages to occur after conception. It is split into three trimesters. I have also included some stages of horse pregnancy pictures to help you see how things develop.
First Trimester Horse Pregnancy Stages
The first trimester in horse pregnancy is from 0 to 90 days. You will see no obvious signs other than the mare no longer having heat cycles. However, some mares still display signs that they are in heat.
During this period, the fetus grows slowly. Here are some great ultrasound images provided by Dr. Patricia Sertich to the MSD Veterinary Manual. They show pregnant mare stages of photos in these early months.
Days 5 – 14 Horse Embryo
At this stage, the embryo is moving around the uterus. The egg sac looks like a black dot in the scan. 
Sonogram of 13-day conceptus – Dr. Patricia Sertich. 
Days 16 – 17 Equine Embryo
This is when the embryo stops moving around and implants itself in the uterus.
Days 24 – 26 Pregnancy Scan Horse
Doing a scan between 24 to 26 days is very important. This is when you can first detect a heartbeat.
Days 35 – 40 Time for Another Scan
At 35 to 40 days of pregnancy, the endometrial cups form. They start creating the hormone ECG, which I mentioned early.
The formation of the cups will prevent the mare from cycling even if the pregnancy has been lost.
This is why it is vital to time to do another scan to see if the pregnancy is progressing or lost.
37-day Conceptus – Dr. Patricia Sertich. 
Days 100 to 120 Retaining Mare Pregnancy
The progestogen is a vital hormone that helps maintain a horse’s pregnancy. At this stage, the placenta is developed, and that, along with the fetus, creates this essential hormone. 
At this stage, the fetus is about the size of a kitten.
READ MORE: Why Do Horses Fall After Mating?
Second Trimester Horse Pregnancy Gestation
Like the first trimester, the unborn foal develops slowly. You might think the fetus is quite large, but it is still fairly small in reality.
Merck Animal Health states that “the fetus grows slowly at approximately 0.2 pounds per day.” 
Not much happens during this time, and you have to worry about keeping your mare healthy, not overfeeding her for ‘two,’ and ensuring she gets plenty of time out in the paddock for no less than 6 hours a day. 
Third Trimester Foal Gestation
The third trimester is when the foal does most of its growth. In these last three months of gestation, growth speeds up a lot.
The foal will gain as much as one pound each day!  A the time of birth, the foal will weigh around 10 percent of the mother’s weight.
During this period, you need to consider changing how you feed your pregnant mare, as now her nutritional requirements are increased.
The third trimester begins at day 226 of pregnancy and lasts until birth around day 340. At around day 270, a horse fetus (some ponies will differ) is around the size of a German Shephard.
However, birth can occur before or after day 340. The safe zone is day 320 of gestation. Foals born before 320 days are usually not viable. 
ALSO CHECK: Horse Sexes Explained
7 Horse Pregnancy Symptoms You Should Know About
Early horse pregnancy can give you little to no indication that it is occurring by just looking at the outside of the mare.
It can take several months before you see any visible signs. The most accurate way to check equine pregnancy early is by ultrasound examination.
However, you will see some, all, or even none of the following horse pregnancy signs as things progress.
#1 The Estrus Cycle Stops
The first sign that a horse is pregnant is that it no longer comes into season. They stop displaying signs of heat, such as urinating small amounts, lifting their tail, and the individual horse’s behavior changes.
Keep in mind some mares will still show estrus symptoms even if they are pregnant.
#2 Behavior Changes
While this is not one of the most accurate signs of pregnancy in horses, she might display personality changes. A sweet mare might become more moody or vice versa.
My mare, a complete cuddle bug who loves other horses, got very protective of her space. However, this only occurred in her third trimester.
Check out this video of a moody pregnant mare.
@moniquedey Honestly so scared everytime I have to catch her 😅 #moody #angryhorse #horsesoftiktok #pregnanthorse ♬ original sound – Monique Dey
At that stage, she would squeal and try and kick any horse that so much as tried to sniff her.
This behavior only started to occur for my mare late in pregnancy. At that stage, she had a pronounced pregnant belly.
Another behavior change is the mare will no longer show any interest in a stallion, and she may even react aggressively towards him.
# 3 Progesterone Hormone Increase Sign of Horse Pregnancy
When a horse is pregnant, the levels of the hormone progesterone increase in the body. You can only know this by taking a blood test which isn’t always accurate.
Here is an excellent video on how to know if your horse is almost due.
@myequestriandream Do you know the signs that a horse is about to give birth? #horse #horsebirth #babyhorse #pregnante #pregnantehorse #fyp ♬ desparado by rhianna – dali 🕊
#4 Stomach Growth
A mare’s stomach will grow as the pregnancy progresses. It might just look like the horse is getting very fat to an untrained eye!
However, the pregnant belly is usually not noticeable until a few months after conception.
RELATED: How Many Stomachs Do Horses Have?
#5 Udder Development During Pregnancy
Udder development is a symptom of equine pregnancy. In the last few weeks of gestation, the udder will get bigger as it prepares to produce milk.
If the udder begins to develop too early, there could be a serious problem, like placentitis, so always call a vet immediately if this happens too soon.
#6 Waxing Udder and Dripping Milk
Just before foaling, a mare’s udder might start dripping milk. It is not ideal if too much milk is dripping, which means essential colostrum can be lost.
Also, in almost all cases, you will see what is called ‘waxing.’ This is a golden-like substance that appears at the end of the teats and looks similar to melted candle wax.
Here’s a video of what the udder looks like.
@georgiaaa25 She’s getting ready to have her baby 🤗 #pregnant #mare #horse #foal #fyl #pregnantmare ♬ Hey Jesus loves you so much repent and turn to him – Gabriel Storm
Waxing can occur a few hours before foaling or for a couple of days.
This is one of the last symptoms of horse pregnancy, and if you didn’t know your mare was pregnant, you won’t have much time to prepare as foaling is imminent.
#7 No Symptoms of Pregnancy
I mention this here as one ‘symptom’ is not a symptom! Female horses are tricky, and some hide their pregnancy well, giving you little to no indication that they are in foal at all!
I found this video on how to tell if your horse is pregnant pretty helpful. Take a look.
How to Take Care of a Pregnant Horse?
You don’t need to change much for your mare at the start of pregnancy.
So long as she gets plenty of time in the paddock, proper nutrition for an average horse, and good hoof care, you should have nothing else to worry about.
Check out this video of a diet for a pregnant mare.
@keequine Mama gets whatever mama wants 💁🏼♀️ We are SO close to her due date y’all! 🥰 #pregnantlife #horsetok #pregnantmare ♬ bee – Burbank
You should also keep her vaccinations and worming up to date. However, some wormers are not safe for pregnant mares. This can go for some vaccinations as well.
So always speak to an equine reproductive vet about this!
Light activity is suitable for a pregnant mare, and you can even keep riding in the early months, but nothing too intensive.
When the mare enters the third trimester, the rapid fetus growth means your mare will need more nutrition. She will require an increase in vitamins, minerals, and food.
There are special feeds formulated for pregnant mares as well as supplements.
If you are unsure, it is a good idea to consult a vet, talk about your specific circumstances, and develop a nutritional plan for this stage of pregnancy.
CHECK: What Do You Use to Breed Horses?
Caring for a pregnant horse is a learning experience that is best carried out with lots of knowledge. To help you on the right track, here are some of the most common questions I’ve come across.
How many months is a horse pregnant for?
On rare occasions, a horse is pregnant for 11 months, sometimes 11.5 months, or even a year. It is both anxiety-inducing and exciting while you wait through those 11 long months of pregnancy!
Can you ride pregnant horses?
You can ride pregnant horses, but you must take care and not overwork her and stop riding in the last trimester.
What does a pregnant horse look like?
A pregnant horse will look very similar to a fat or obese horse. Many will begin to look like their stomach has dropped down. In early pregnancy, the horse will look like any other horse.
What time of day do horses give birth?
Most horses give birth in the middle of the night. This is because they are prey animals in the wild world, and it was safer under cover of darkness for a mare to have her foal.
Check out this video on how horses give birth.
@brrobinette #horsebirth #birthinproblems #foalsoftiktok #foalemergency #vettok #foalcast ♬ I Just Want to Be the One You Love – Cryst
I hope you are now off to a great start learning about horse pregnancy. There is so much to learn, and it is a fascinating topic.
Have any of my readers bred their foal? I’d love to hear all about your experience.
- 1. Pregnancy Determination in Horses – Management and Nutrition. Veterinary Manual. https://www.msdvetmanual.com/management-and-nutrition/management-of-reproduction-horses/pregnancy-determination-in-horses
- 2. Equine Reproduction From Conception to Birth | AAEP. aaep.org. Accessed March 28, 2022. https://aaep.org/horsehealth/equine-reproduction-conception-birth#:~:text=All%20horses%20should%20be%20examined
- 3. How Can I Tell if a Mare is Pregnant? The Horse. Published December 13, 2017. Accessed March 28, 2022. https://thehorse.com/149581/how-can-i-tell-if-a-mare-is-pregnant/
- 4. Foal Care | Pregnancy | Merck Animal Health USA | Merck Equine. www.merck-animal-health-equine.com. Accessed March 28, 2022. https://www.merck-animal-health-equine.com/programs/mare-care/pregnancy
- 5. Pregnant Mares and Foaling. Severn Edge Vets. Accessed March 28, 2022. https://www.severnedgevets.co.uk/blog/pregnant-mares-and-foaling
- 6. Intro – Length of Gestation. www.ansci.wisc.edu. Accessed March 28, 2022. http://www.ansci.wisc.edu/jjp1/equine/parturition/intro.html
- 7. How to Palpate a Mare for Pregnancy. NexGen Pharmaceuticals. Accessed March 28, 2022. https://nexgenvetrx.com/blog/equine/breedingproducts/how-to-palpate-a-mare-for-pregnancy/
Siun is an all-around animal lover, with a passion for horses. She grew up in the United States, competing in the hunters, equitation, and jumpers. Now living in Ireland, she competes with her own showjumping horses. She is experienced in the care and training of horses, as well as teaching riding lessons. She loves to combine her love for horses with her work. When not working, Siun will be found at the stables, rain or shine.
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