How do they breed horses? A great question and one that can get more complicated than you might think.
By breeding my own horses and doing extensive research, I’ve learned that there is so much more to it than simply leaving them to it, especially when it comes to valuable sport horses.
I wanted to put together an easy-to-follow overview to share what I’ve learned, so let’s dive right in!
- There are 5 ways to breed horses
- ICSI is the most expensive horse breeding option
- Mares and stallions must be managed correctly and in good health
- Artificial insemination is the most common horse breeding technique
How Do They Breed Horses
When it comes to horse breeding, you will see that producing that beautiful foal involves a lot of thought well before conception.
As science progresses, the methods one can use to breed horses also move forward and becomes more complicated.
Methods of Mating
There are five main ways horses are bred. The specifics of each method can vary slightly, and the costs can vary extensively. Which method of mating you choose will depend on your budget, the horse breeds involved, and the goal.
So, are you ready to dig deeper into how horses are bred? First, let’s look at one of the most common horse breeding methods used for sport horses.
CHECK: HORSE MATING BEHAVIOR
1. Artificial Insemination
Artificial insemination is an extremely popular breeding process for sport horses. It gives horse breeders much more choice and access to top stallions around the world.
It does, however, increase the cost. The cost will vary depending on where you live, but you can expect to pay $500 or more per cycle plus the stud fee.
It is great if your mare gets pregnant on the first try, but it can commonly take more than one cycle, which quickly increases the cost.
So how do you artificially breed a horse? First, mare owners need to choose the stallion and decide if they want to use fresh, chilled, or frozen semen.
You then need to track your mare carefully, which involves regular scans from the vet to time the AI process as best as possible. When the mare is ready, a vet will then insert the semen into her uterus.
Fresh semen has the best success rate but requires quick work and excellent communication between the horse owner, vet, and stallion owner. 
When you use AI, the mare and stallion never meet. In fact, they could live hundreds, even thousands of miles apart. AI is used for many horse breeds, including the American Quarter Horse, warmbloods, and Arabian horses.
For Thoroughbred racehorses, AI is not allowed if you want to register with the Jockey Club for horse racing. One reason for this rule is that it helps keep genetic diversity.
To see a vet using artificial insemination, check out this video. Though if you are squeamish, you may not want to watch.
2. Embryo Transfer
In the last few years, embryo transfer for sport horses has been used more and more by horse breeders. This is a more complicated breeding process than AI. First, the mare is artificially inseminated, but then after a few days, she is flushed.
The goal of the flush is to remove, hopefully, an embryo. If there is an embryo, it is then implanted into another mare. That mare, the surrogate, will then carry the foal and nurse it when it is born.
Using this way requires a vet that specializes in breeding. It also adds more to the cost. It is a good way to get a foal from a really good mare that is still competing or for horses that, for some reason, can’t carry their own pregnancy.
It also means that it is possible for mare owners to get more foals from good horses as more than one embryo can be taken a year as opposed to the maximum of one foal if the mare carries a foal herself.
ICSI (Equine Intracytoplasmic Sperm Injection) is the most recent advance in horse breeding and also the most expensive. It does have some advantages but is best used for particularly special horses.
This method takes an oocyte from a mare and injects it will a single sperm. All this is done in a lab. It is then hoped that the sperm will fertilize the oocyte and create an embryo.
Once the embryo develops, it is then placed in the donor or surrogate mare. It can also be frozen for future use.
This method opens up doors to using stallions that are deceased with very little frozen semen left or for those with poor fertility. You would only use this method to breed mares in order to access particularly talented stallions or breed extra special horses that have a specific genetic diversity.
The University of Colorado describes the process as follows:
“The ICSI procedure involves micro-injection of a single sperm cell into the cytoplasm of a mature oocyte, which physically causes fertilization. The fertilized oocyte is returned to an incubator and allowed to develop into an embryo, which usually occurs within 6-8 days.” 
See ICSI at work in this cool video.
4. Natural Cover
Natural cover is when a mare is brought to a stallion, and they meet in person. You still need to track the mare’s cycle and present her to your chosen stallion at the right time so she will accept him.
This method is more natural than the ones I mentioned above, as the horses are allowed to mate as they would normally but in a controlled environment.
Both the mare and stallion are controlled during the process to reduce any risk of injury. Natural cover is the only way Jockey Club thoroughbreds are allowed to breed.
5. Running a Stallion With Mares
Running a stallion with mares is the closest to how horses breed in a natural environment. A group of mares is turned out with a single stallion who will mate with them when they are accepting.
I’m personally not a fan of this method despite its appealing, more natural way, as it is too risky for the animals involved. But many people will use this way to breed horses, and it has the highest success rate in getting a pregnant mare.
Things To Consider When Breeding Horses
Two of the most important things to consider before using any horse as a breeding animal are why you want to do it and does the horse have the right qualities to produce what you’re looking for.
As cute as foals are, you shouldn’t just breed your mare because you love her or pick any stallion. It is important to match the stallion and mare to improve them in conformation, temperament, and ability.
At the end of the day, you want a nice foal that will not have health issues and will make a safe riding horse. This gives them a much better chance at a happy life and reduces the risk of them ending up in the slaughter chain.
You should implement some selective breeding and avoid using a grade horse. A grade horse has no lineage recorded and is usually the result of a lack of breeding thought.
That’s not to say those horses don’t make fantastic riding animals, but they often have less than ideal conformation, and you have no way of knowing if they carry genes that can cause issues.
If you have a mare or stallion that is good enough to breed, there are a few more things you need to consider, so let’s take look.
If you are following a good breeding process, you will only be using suitable breeding animals. This means that checking the performance record of sport horses is an essential part of the process.
For racehorses, you want to check the racing performance record.
These records should be above average. While it is still common to breed mares that have no performance record, these mares still have a high standard of lineage and qualities.
Overall Health Of The Mare
First, let’s start with the mare. To be a quality breeding animal, she needs to be in overall good health, have decent hooves, be up to date with vaccinations and worming, and be an appropriate age, especially for a first foal.
The mare should be a mature horse of at least 3 years old. If a mare is older, in her teens, and has never had a foal, she has more risk of complications and is harder to get in foal.
Once you know that the mare is healthy, you need to do a breeding soundness exam. This is done by a vet who will check if the mare’s reproductive system is healthy enough to carry a pregnancy.
You will also need to track the mare’s cycle and when she ovulates to know when she is ready to breed.
You should always do this as there can be hidden infections or other issues that can prevent a mare from getting pregnant. Many of these can be fixed by a vet, and doing this exam will save you time and money in the long run.
Overall Health Of The Stallion
Not only does the mare need to be healthy, but so does the stallion. This requires special management practices to ensure fertility is maximized.
A vet can carry out fertility tests on the stallion’s semen to see sperm numbers and motility.
Feeding and Management
Feeding and management also play an important role in how horses are bred. During horse breeding season, a stallion needs high-quality feed at the same rations you would give to a horse in hard work. 
The stallion also needs exercise and plenty of time grazing outside in a sturdy, safe paddock. This also applies to mares. While mares don’t need ridden work, the effects of exercise include a healthier pregnancy and foaling.
Mares do not need extra feed if they keep their weight and health on a ration that non-breeding horses get. It is only in the last three months of pregnancy that mares are given supplementary feed, as this is when the foal develops the most in utero.
Tracking The Mare’s Estrous Cycle
As I mentioned above, you will need to track the mare’s cycle. This includes some things that you can observe on a day-to-day basis, such as when she is in season (heat), and other things, such as scans, that the vet must do.
Tracking the cycle will help you spot any reproductive issues and know when the mare is ready for AI or live cover.
Decide The Best Time To Breed
The best time to breed is when you have a healthy mare and the right time of year. Most foals are born in the spring. This allows for them to spend most of their time outside, which is very important for growing foals.
It also means both the mare and her baby can graze on grass as much as possible, improving their overall health.
Since the gestation period for a mare is 11 months of pregnancy, breeding from April to June is the best time.
What is hand breeding a horse?
Hand breeding a horse is the same as natural cover. The mare and stallion meet to breed but they are both handled by people to keep the environment as safe as possible.
What is the most common way to breed horses?
The most way to breed horses is artificial insemination, followed by natural cover.
How long is a horse pregnant for?
A horse has a period of 11 months of gestation. The days of pregnancy can vary depending on the mare, but the average is 345 days.
I hope this guide has helped you learn more about ‘how do they breed horses’. As you can see, a lot of thought and care goes into the process when done correctly.
Science has given us ways to access stallions that might no longer be available. When you start to dive deeper into horse breeding, you can really go down a rabbit hole. Genetics and choosing the best pairings are really interesting.
If you have any questions, leave them in the comments. I’d love to hear from you!
- Surgeons RV. Artificial Insemination (AI) [Internet]. Rossdales Veterinary Surgeons. 2020. Available from: https://www.rossdales.com/services/sport-and-leisure-horses/breeding-services/artificial-insemnation-ai
- Equine Intracytoplasmic Sperm Injection (ICSI) [Internet]. csu-cvmbs.colostate.edu. [cited 2022 Oct 7]. Available from: http://csu-cvmbs.colostate.edu/academics/bms/equine-reproduction-laboratory/Pages/equine-intracytoplasmic-sperm-injection.aspx
- Horse Breeding Basics – Extension Horses [Internet]. horses.extension.org. Available from: https://horses.extension.org/horse-breeding-basics/
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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