The Complete Guide to Horse Breeding – 8 Facts, Behavior and Cycle

Do you know that 57% of the horse breeders earn approximately $100k per year? Horse breeding has been an essential phenomenon since the medieval ages as it increases a horse’s traits.

All About Horses: A Kid's Guide to Breeds, Care, Riding, and More!
  • Halls, Kelly Milner (Author)
  • English (Publication Language)
  • 80 Pages - 06/29/2021 (Publication Date) - Rockridge Press (Publisher)

The selection of horses for breeding mostly includes purebred horses of a breed. We have used planned breeding for hundreds of years to produce specifically favored traits in horses.

If you are a horse breeder and want to go through a healthy breeding process, we understand your aspirations. 

In this article, we are going to give you a complete guide to horse breeding. 

Horse Breeding Basics

We start by clearing out the basic terminologies that you’re going to see in this article. The stallion, also commonly known as the sire, is the male parent of a horse. 

  • The mare, also called the dam, is the female parent of a horse. 
  • The foal is the offspring that contains the genetic composition of the stallion and the mare. 
  • Colt refers to a young male horse only, and filly refers to a young female horse only.
  • The terms “half-brother” and “half-sister” refer to horses from the same dam. 
  • The “breeder” is the owner of the mare at the time of foaling

The stallion’s role is to deliver healthy sperm(that contains his genetic information) into the vagina of the mare. A healthy stallion should have enough libido to service regularly and produce healthy sperm throughout the breeding season. 

Consequently, the mare’s role is to participate in the mating process and carry healthy offspring in its womb. 

Therefore, your role as the breeder is to take special care of the mare because the health of the desired offspring depends on the mare’s health. 

We’re going to cover the whole breeding process in more detail down below, so keep reading. 

The Breeding Behavior of Horses   

You need to evaluate the reproductive behaviors of horses for identifying breeding potential or problems in the horses.

Horse Breeding

It’s important to understand the sequence of behaviors of the horse before, during, and after mating to diagnose problems such as poor libido(sex drive), erection, or ejaculation failure. 

Therefore, learning about the behavioral signs is very useful in training a novice stallion or mare for mating and applying behavioral correction techniques. 

The Breeding Behavior of Stallions

The breeding behavior of the stallion can vary depending on whether the stallion is in a feral environment or a domestic environment. 

It has been observed that domestic stallions are cooperative and responsive with adequate sexual arousal and response. However, they are still sexually responsive to teasing even when handling is restricted.

Feral Environment

The reproductive behavior of the stallion in a feral environment can be divided into two parts:

Harem formation and maintenance

The harem group usually consists of one stallion and several mares and their offspring. 

The harem stallion exhibits controlling behavior to keep the group together and keep horses from other harems away from the group. 

He is known to exhibit keen attentiveness to potential threats and intrusions. 

Courtship and mating 

When a stallion is sexually aroused, it approaches a mare of the harem group with an arched neck and raised tail. The stallion shows repeated interest in the mare in the days preceding estrus(when the mare is in heat). 

These early courtship interactions are aggressive. That’s why the mare might exhibit hostile behavior such as kicking, threat posturing, biting, or squealing towards the stallion. If the mare continues to show aggressive behavior, the stallion moves away.

The pre-copulatory (before mating) interactions can last for hours or days before copulation (mating). The copulatory interaction often occurs in less than 1 minute.

The stallion shows no interest in breeding for a certain period after ejaculation. But this period varies a lot depending on the individual sexual traits of a stallion.

Domestic Environment

The breeding behavior of horses is limited in the domestic environment. In a controlled breeding environment, mate selection and pre-copulatory behaviors are mostly affected. 

Domestic stallions are usually maintained in physical separation from other horses. Besides, interaction with mares is always bound to regulated access to mares that are to be bred. 

In the domestic setting, there are generally three breeding arrangements :

  1. Pasture mating
  2. In-hand mating
  3. Semen collection 

In all three arrangements, domestic stallions seem to be cooperative. The stallions show adequate sexual arousal and response even under difficult breeding environments.

They exhibit sexual response during teasing despite handling constraints. They promptly achieve and maintain erections during breeding and tolerate the washing of their penis.

During semen collection, they mount a mare or a dummy when directed by the handler and ejaculate into an artificial vagina. Generally, the individual stallions show consistent responses over time

The Breeding Behavior of Mares

Harem mares of a feral environment continuously interact with the stallion all year round. The frequency of sexual interactions may vary from time to time. 

In domestic breeding arrangements, the mare is in more control of the mating location, stimulating the stallion and the timing of breeding.  

Typical estrous mare “presentation” includes: 

  • Exposing the clitoris
  • Frequently expelling urine
  • Lifting the tail
  • Rhythmically averting the vulva
  • Squatting
  • Vaginal fluids

They also stay near the stallions when in full heat.

The Breeding Behavior of Geldings

Some of the biggest effects of testosterone happen long before a horse is castrated.

When a male horse is a fetus, the fetus’ testes pump out androgens that act on his brain to masculinize it. The result of this early influence doesn’t go away when a male horse is castrated. That is why geldings often behave like stallions around mares.

They even exhibit the flehmen response (curled up top lip) to express their interest in the mares. Other common breeding behaviors in geldings include trying to mount mares, fighting with other geldings, showing aggression, etc. 

The Estrous Cycle in Mares

A mare is said to be going through her estrus cycle when she is ovulating.

Ovulating is common in all mammals. It is the time when the possibility of conceiving a child through mating is the highest. 

The estrous cycle regulates the receptive behaviors of the mare towards a male horse. The purpose of this cycle is to prepare the mare for conception physically. 

The natural breeding season for horses in the northern hemisphere occurs during the spring and summer months when mares have several estrous cycles. 

  • Each cycle lasts approximately 21 days. 
  • After each estrous cycle, a mare enters the estrus or heat stage. 
  • The heat stage can last from 2 to 10 days. 
  • During a season, the cycle may repeat 3 to 4 times until the mare conceives.

Horses breed during the long summer days. While some mares cycle during the winter, the majority of mares are anestrous during this time.

8 Steps for Breeding Your Mare

Breeding requires the proper procedure, and it comprises eight essential steps that have to be followed to get desired results with minimum complications.

Step 1: Evaluate the mare’s overall health.

The first and most important thing about breeding a mare is that there is no single recipe for broodmare management; each needs individual veterinary attention.

Before focusing on a mare’s reproductive health, owners should take note of her overall health and wellbeing. 

Here’s what you should keep in mind:

  1. Does she appear to be in good health?
  2. Is the condition of her hooves favorable?
  3. What vaccinations does she need? Is it necessary for her to have a fecal egg count done to screen for parasites?
  4. Is she in need of a dental examination?
  5. We are evaluating the Henniker body condition score (BCS) of the mare. 
  6. Before breeding, broodmares should ideally score between a five and a seven on a 1-to-10 scale.
  7. A complete check of the mare’s medical history. 
  8. Continued vaccinations after pregnancy as suggested by the American Association of Equine Practitioners. 

Step 2: Breeding Soundness Examination 

Before breeding, veterinarians usually perform a breeding soundness test—an examination of the reproductive system in broodmares—to identify and treat any potential issues. 

We can obtain any further information a veterinarian may want by doing a hysteroscopic exam. 

This exam includes inserting an endoscope into the uterus and looking for irregularities like foreign items, adhesions, or fungal/bacterial plaques.

After the test, your veterinarian may be able to prescribe certain management strategies or treatments before breeding.

Step 3: Get the mare cycling.

You must ensure that your mare is cycled properly before breeding.

Mares are seasonally polyestrous. This means they cycle and ovulate throughout seasons of extended day length, such as spring and summer. Some mares, on the other hand, cycle all year.

Although many breeders, particularly thoroughbred breeders, attempt to conceive their mares in late winter or early spring to foal early in the year.

As a result, you may need to get the mare cycling throughout the winter, when she would typically be in anestrus (a time of no estrus). Mares can be stimulated to cycle by breeders using methods such as artificial lighting and hormone treatment.

Step 4: Tracking the estrous cycle of the mare

The estrous cycle lasts 21 days. However, she will only come into heat and be susceptible to breeding during the cycle’s first five to seven days.

During the last 24 to 36 hours of behavioral estrus, ovulation occurs.

Knowing when a mare is in heat helps the veterinarian estimate when to check the mare for follicles. This information can determine ovulation and the timing of breeding, whether by natural cover or artificial insemination (AI).

Step 5: Determining the Breeding Time

Once a mare has begun to cycle, the owner must decide to breed her during the first heat—the less usual option—or wait for future heats, which have greater pregnancy rates. 

Things to keep in mind when determining the breeding time:

  1. For a thoroughbred racehorsethe foal should be born as near to 1st January as feasible.
  2. Use different breeding methods (live cover or AI).
  3. AI breeding is influenced by whether you use fresh, chilled, or frozen sperm. 
  4. Fresh sperm has the best fertility rates. But it cannot be transferred and must be utilized immediately.
  5. Cooled sperm viability varies depending on the stallion. 

But it is generally acceptable for 36 to 48 hours from collection until insemination.

In these methods, the veterinarian prepares the mare to ovulate within 24 to 40 hours of insemination. Insemination has the lowest success rates because it must occur within six hours before or after the time of ovulation. 

Step 6: Utilize veterinary technology to precisely time breeding to coincide with ovulation 

Another way to get a mare pregnant sooner than her cycle is to “short-cycle” her off the first foal heat. The veterinarian can do this by prescribing exogenous prostaglandins and accelerate the process of her getting back into heat.

The typical 14 to 17 day waiting period between estrus cycles gets shortened to six days.

However, it can take longer depending on the follicle size of the mare when she receives prostaglandin. 

Step 7: Facilitate Uterine Cleansing After Birth

Each time a mare is bred, her body initiates a spontaneous inflammatory reaction. This reaction occurs mainly during the first 12 hours after breeding to clear the uterus of dead sperm, inflammatory cells, debris, and pollutants.

Under natural conditions, the body of a mare can clean up after multiple breeding. But artificial environments affect the clearing process that results in chronic post-breeding endometritis (inflammation of the uterus).

Since gravity is not on their side, the mares who have given birth to several foals and have a stretched uterus may struggle with this natural cleaning process.

The uterus of a young mare is elevated above the pelvis, allowing pollutants to be cleared more efficiently through the cervix, vagina, and vulva. 

When a mare has several foals, the uterus may fall below the pelvic level, hindering uterine clearance by causing the fluid to travel “uphill.” Therefore, veterinarians recommend that broodmare managers take freshly bred mares out to let them roam about. 

There are also specialized medicines that help the broodmares in cleaning their uterus after each birth. 

Step 8: Pregnancy Check

Once the breeding process is complete, the last step is to ensure her pregnancy. A veterinarian can confirm the pregnancy via ultrasound after 14 to 15 days of ovulation. 

If your horse is not pregnant, the veterinarian can investigate and treat probable causes before breeding her again.

Methods of Equine Breeding

The three most popular methods of equine breeding are:

  • Pasture Mating
  • In-Hand Mating
  • Semen Collection
Pasture MatingIn-Hand MatingSemen Collection
1. The stallion is allowed to freely interact with two or more mares in an outdoor paddock.1. This is the most popular type of natural cover in the modern equine breeding industry.  1. Semen collection is also known as semen insemination.
2. Adjustment is quick when they’re moved from one paddock to another with different groups of mares.2. The interaction between the stallion and the mare is completely supervised and controlled.2. Usually, stallions are trained to mount a dummy mare.
3. They breed every 1 to 2 hours during the breeding season.3. Usually, the stallion is directed to approach the mare from behind, skipping the main part of the precopulatory sequence.3. The stallions trained in this manner do not lose their natural breeding abilities.  
4. The pregnancy and foaling rates are usually good if the stallion doesn’t have any physical or genital problems.4. Stallions in this system learn to do their job without precopulatory behavior.4. Training a novice stallion for semen collection using an artificial vagina or an estrous mare is found to be successful in 90% of cases after one or two experiments.

Horse breeding with donkeys

There are two types of animals bred from the breeding of a horse and a donkey :

  • Mule
  • Hinny
Mule  Hinny
1. A mule is the offspring of a male donkey (jack) and a female horse (mare).1. A hinny is a domestic equine hybrid that is the offspring of a male horse (a stallion) and a female donkey (a jenny).
2. Mule is the relatively easier one to breed.2. It is relatively harder to breed.
3. The size of a mule and the type of work assigned are highly dependent on the mule’s mother’s genetics (dam).3. The hinny differs from the mule both physiologically and in temperament.
4. The mule has the dam’s size and ground-covering abilities. Also, it is stronger than a horse of comparable size.4. Hinnies are comparatively less valued in the industry.
5. The mule also inherits the donkey sire’s endurance and temperament. It also requires less food than a horse of comparable size.5. The hinny is weaker than the mule and also less efficient in work.

Frequently Asked Questions (FAQ)


Because horses reproduce according to the seasons, breeding behavior can be seen in the spring and summer when there are more daylight hours.

Estrus cycles are the heat cycles that mares go through before presenting themselves to stallions. They try to become pregnant by copulating many times.

Mares and stallions are paired on farms so that there is no competition between the stallions, which is normal in the wild where the dominant horse will breed all the mares when they are in heat.

If you have any thoughts about our article or any personal experience, let us know in the comments below.

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