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Breeding Mare: How Do You Breed Horses

Breeding horses isn’t just an art; it’s a science where every decision can influence generations. With over two decades in the equine breeding industry, my journey has unveiled the intricate dance of genetics, timing, and care essential for success.

If you’re navigating the complexities of breeding your mare, this article is your compass.

From selecting the right stallion to understanding the nuances of mare care, we’ll guide you through each step.

How to Manage Your Broodmare Well

Breeding horses isn’t just about putting a mare and stallion together. It’s a specific part of vet care focused on helping horses reproduce.

Even if your mares and stallions are healthy, there’s no guarantee they’ll have a foal. It’s especially true for first-time mares, older ones, or those that find it hard to get pregnant. Working closely with a vet and following a plan for each mare can really help improve your chances of adding a new foal to your stable in the spring.

Step 1: Checking the Mare’s Health Before Breeding

Check the Mare's Overall Health

Start by making sure the mare is healthy. Check if her hooves are in good shape, if she’s up to date on shots, and if she has any parasites by doing a fecal egg count. Also, see if she’s at the right weight and needs any dental work.

It’s important for broodmares to have a Body Condition Score (BCS) between 5 and 7 before they’re bred. You should be able to feel the mare’s ribs but not see them. Also, look out for any health issues like PPID or insulin problems that might make breeding harder.

Go over the mare’s history of getting pregnant, any uterus issues, or times she didn’t stay pregnant.

For live cover breeding, check what the breeding place requires. They might want your mare vaccinated against certain diseases like rhinopneumonitis to keep the stallion safe. Keep her vaccinations up to date, even when she’s pregnant.

To lower the chance of the mare losing the baby, the experts recommend giving her a vaccine against herpesvirus-1 at five, seven, and nine months into the pregnancy. On farms where lots of horses are bred, they might vaccinate even more often, but that’s not the usual way to do it.

Step 2: Conducting a Breeding Soundness Exam

Breeding a mare involves close collaboration between the owner and the vet. A crucial step in this process is the breeding soundness exam, which vets perform to identify and address any issues before breeding.

Consider your budget and discuss with your vet the various tests available. Sometimes, a mare may only need a thorough breeding soundness exam after failing to conceive after several attempts.

This evaluation is particularly critical for mares who have difficulty conceiving or are older. Its purpose is to pinpoint problems or provide insights, enabling the owner to make well-informed decisions.

For mares without known breeding issues, the vet begins by examining the reproductive anatomy, paying special attention to the perineal conformation. Poor perineal conformation increases the risk of contamination, which can be mitigated by procedures like Caslick’s, where the vulvar lips are sutured together, then opened for breeding and foaling.

The exam also assesses the mare’s estrous cycle and examines her ovaries using transrectal palpation and ultrasound. These techniques can detect uterine or vaginal abnormalities, such as excessive fluid indicating inflammation or inadequate uterine clearance.

Ultrasound exams are standard practice, offering a detailed view that aids in managing the breeding process. It’s essential for understanding the mare’s reproductive health and guiding further testing.

Mares with a history of reproductive challenges, including those with “baggy, saggy” uteruses, often undergo additional tests to evaluate for inflammation and infection. This is especially true for older mares, those that have birthed multiple foals, or have had previous uterine inflammation, as they may face higher risks of post-breeding inflammation.

A biopsy of the uterine lining can reveal conditions like inflammation, scar tissue, and enlarged lymph vessels. This test allows the vet to assess the mare’s chances of conceiving and carrying a pregnancy to term.

In cases requiring further investigation, a hysteroscopic exam may be performed. This involves using a small camera to inspect the uterus for abnormalities such as foreign bodies, scars, or microbial growths.

The insights gained from the breeding soundness exam enable the vet to recommend specific management practices or treatments to optimize the mare’s chances of successful breeding.

Step 3: Getting the Mare Ready for Breeding

After your vet takes care of any breeding issues, you need to check that your mare is ready to breed. Most mares are ready in the warmer months, but some can be ready any time of the year.

Some breeders, like those in horse racing, aim to have their mares give birth early in the year. To do this, they get their mares to start their cycle in winter, when they normally wouldn’t. Using special lights or hormone treatments can help kickstart this process.

When the days get longer, or we use artificial light or hormones, the mare’s body reduces melatonin. This change triggers the release of a hormone called GnRH. GnRH tells the brain to make two other hormones, FSH and LH, that help the ovaries get ready.

The mare’s ovaries will keep making and losing small egg pouches called follicles until one big one takes over. This big one produces enough of a hormone called estrogen to start the mare’s breeding cycle. Then, LH makes this big follicle release its egg. This process moves the mare from not being in cycle to starting her cycle, usually taking about 60 days to get to the first ovulation.

Step 4: Monitoring the Mare’s Estrous Cycle

The mare’s estrous cycle lasts about 21 days, with a fertile period of five to seven days early in the cycle. The critical moment for breeding, ovulation, occurs in the final 24 to 36 hours of this fertile window.

Aiming to breed as close to the time of ovulation as possible is key for increasing the chances of successful conception.

Knowing when a mare is in heat is essential for planning the timing of breeding, whether naturally or through artificial insemination (AI). To identify when a mare is ready, observe her behavior around a teasing stallion. Indications of heat include interest in the stallion, vulvar winking, adopting a breeding stance, lifting her tail, and frequent urination. On the other hand, a mare not in heat may pin her ears back, clamp her tail down, act aggressively, or ignore the stallion entirely.

Step 5: Choosing the Right Time to Breed Your Mare

After your mare starts her cycle, it’s time to pick when to breed her. It’s usually better to wait for later heats than the first one because they often lead to higher chances of pregnancy. If you’re breeding a racehorse, you’ll probably want the foal born near January 1.

Whether you choose live cover or artificial insemination (AI) affects your timing:

  • Fresh Semen: This is most effective but needs to be used right away.
  • Cooled Semen: This can last about 36 to 48 hours, so you should aim to have the mare ready to ovulate about 24 to 40 hours after you inseminate her.
  • Frozen Semen: This is the hardest to time right. You need to do the insemination within six hours before or after she ovulates, which can be a bit tricky and might not work as well.

Using cooled semen means you need to know when the stallions are collected and how the semen is sent—like by plane or overnight shipping. This helps you line up the insemination with the mare’s ovulation time, making sure everything’s ready when the semen arrives.

Step 6: Syncing Breeding Time with Ovulation Using Vet Techniques

If you’re looking to get a mare pregnant quickly or just want to keep track of her cycle, your vet can use a trick called “short-cycling.” This is useful if you’re breeding her again right after she’s had a foal. The vet gives her a special medicine that makes her ready to breed sooner than usual, cutting down the waiting time that normally lasts about 14 to 17 days. How soon she’s ready depends on how big the egg-carrying part (follicle) is when she gets the medicine, usually about six days after the egg is released.

  • If the follicle is about 25mm, she’ll be ready to breed in four to five days, and then it takes another three to four days for her to release an egg.
  • If the follicle is bigger, like 35mm, she’ll be ready in two to three days, and will release an egg in another two to three days after that.

There’s also a way to make sure she releases an egg right when you want her to. This involves giving her another kind of medicine. Think of it as a way to make sure everything goes as planned.

Once she starts showing she’s ready, it’s good to check on her a lot. The more you look, the better you’ll understand her cycle. For mares that need special timing, like when using frozen semen, you might even check three times a day to learn exactly when the best time to breed is.

When you know the best time to breed, have your vet take care of the breeding, whether it’s the natural way or using artificial insemination. If the vet notices any fluid in her uterus, it might mean there’s a problem that needs looking into.

Read: The Most Expensive Quarter Horse

Step 7: Helping Mares Clean Out After Breeding

After breeding, a mare’s body gets rid of stuff it doesn’t need, like dead sperm and other debris. Usually, nature takes care of this, especially if a mare breeds a few times.

But, when we breed horses in a controlled way, sometimes this natural cleanup doesn’t work as well. This can cause inflammation if the mare’s body doesn’t contract right or if the cervix doesn’t open properly to let fluids out.

Mares that have had a lot of foals might have a harder time with this cleanup. Their uterus can sag, making it tough for fluids to get out because of gravity. Younger mares don’t usually have this problem because their uterus is in a better position to clear things out.

Moving around helps mares clean out naturally after breeding. If needed, giving medicine like oxytocin, doing a special cleaning called uterine lavage, or even acupuncture can help the uterus contract and clean out. For mares that have a hard time because their cervix won’t relax, there are medicines to help with that, too. This is really helpful for older mares or those that haven’t had foals and have a tight cervix.

Step 8: Confirming Pregnancy

Once your mare has been bred, the crucial next step is to find out if she’s pregnant. Around 14 to 15 days after she ovulates, your vet can perform an ultrasound to see if the breeding was successful.

If it turns out the mare isn’t pregnant, your vet will investigate the reasons behind it. Understanding why can help fix any problems, getting everything ready for another breeding attempt.


In the realm of horse breeding, patience, knowledge, and a deep respect for the process define the path to success.

Our journey through the nuances of equine reproduction reveals that blending science with intuition leads to the most rewarding outcomes.

Whether you’re a seasoned breeder or just beginning, remember that every mare and stallion brings a unique set of traits to the lineage they create. Embrace the challenges, celebrate the victories, and always prioritize the well-being of your horses.

Armed with the insights shared, you’re now better equipped to embark on your breeding endeavors with confidence and a sense of purpose. Forge ahead, and may your passion for horse breeding flourish.

Picture of Dr. Noman Tariq

Dr. Noman Tariq

Dr. Noman Tariq, a seasoned veterinarian with a DVM from ARID University and an MPhil in Animal Nutrition from UVAS, specializes in equine health. His deep passion for horse nutrition and well-being drives his work, offering invaluable advice for horse owners. Dr. Tariq's expertise ensures horses lead vibrant, healthy lives.
You can read my full bio here

Breeding Mare: How Do You Breed Horses