| Equestrian Space

Many people who are unfamiliar with horse mating are curious to know more but are too shy to ask an experienced horse professional about the ins and outs (no pun intended) of horse mating. This post provides a comprehensive introduction to the normal processes of wild horse mating and how humans have influenced the process.

Horse mating occurs in three phases, courtship, copulation, and post-mating behavior. Courtship allows the stallion to test the mare’s receptivity. Copulation occurs when the stallion’s erect penis is inserted into the mare’s vagina and is completed once the stallion ejaculates and dismounts.

There is nothing cuter than a curious newborn foal bouncing along next to their dam. However, the process of getting that foal conceived often leaves new horse owners wide-eyed and more than a little nervous. Facilitating successful horse matings is not for inexperienced horse handlers, the faint of heart, or those who are squeamish about bodily functions!

How Do Horses Mate: The Three Phases Of Sexual Behaviour

Mating between horses occurs in three stages, courtship, copulation, and post-mating behaviors.

Courtship Between Mating Horses

The initial phase of courtship is characterized by high levels of aggression displayed by both the mare and the stallion; as the mare’s receptivity increases, aggression between the mating pair will subside before copulation.

Stallions tend to have “sex on the mind” and will closely monitor “their” mare for signs of her coming into season. As the mare approaches estrus, the stallion will continue to check her receptivity to his advances.

He will frequently prance up to her with his ears pricked and neck arched. The dominant stallion may also nicker or whinny when he sees the mare.

As the stallion approaches the mare, he will extend his head and neck to sniff her. Initially, the stallion will approach the front of the mare and sniff along her face, neck, withers, and front legs. The stallion will often squeal and chop (i.e., kick out with his front legs) or spin away, kicking out at the mare.

How Does A Mare Show She Is Not Ready To Mate?

Non-receptive mares will return the stallion’s aggression and will:

Flatten her ears
Bite, kick or rear at the stallion
Attempt to flee from the stallion
Clamp her tail down over her perineum, preventing access to her vagina

Most stallions will move away and leave the unreceptive mare alone, as mating with an aggressive mare can severely injure the stallion. For a wild stallion, an injury is often the difference between keeping and losing his harem of mares.

However, aggressive stallions have been known to force matings by chasing unwilling mares until the exhausted mares give up and permit the stallion to mount them.

Young or anxious mares often prefer to be covered by younger, more inexperienced stallions who have a less aggressive approach. Mature stallions may force a covering on a fearful mare who is in full estrus but continues to rebuff his advances.

How Does A Mare Show She Is Ready To Mate?

Unlike a non-receptive mare who meets the stallion’s aggression with her own, a receptive mare shows more submissiveness when approached by the amorous stallion.

A receptive mare will present her backside to the stallion, move her tail to the side, squat, and rhythmically evert her vagina. The eversion of the vagina is often referred to as “winking” and is frequently accompanied by small qualities of urine.

The mare will actively seek out the stallion and engage in mutual grooming, sniffing, licking, and nuzzling.

Once the mare indicates her receptivity to the stallion’s advances, the stallion will begin sniffing and nipping along her flanks, back legs, and vulva. Stallions show a flehmen response if exposed to the mare’s pheromone-laden urine.

Before penetration, stallions will frequently do a “test run” or dry cover. The stallion mounts the mare during a dry cover without extending its penis; his penis remains safely tucked in its sheath.

The dry cover allows the stallion to be sure that he has read the mare correctly and is not risking the crown jewels by covering a mare who might kick during a vulnerable moment.

Copulation Between Mating Horses

Once the stallion is convinced that the mare will stand to be mounted, the stallion is ready to get down to business and do the deed.

As the stallion explores the mare by sniffing, licking, and nuzzling her, the olfactory stimulation gradually leads to the development of his erection. Once fully erect, the stallion may mount the mare from behind or laterally.

If the stallion mounts the mare from the side, they will use small hopping motions to reposition themselves. Lateral mounting is more common amongst young, inexperienced stallions.

Once the stallion is correctly positioned, he will grip the mare with his forelegs while bringing his head close to her neck. Some stallions attempt to stabilize themselves by biting the mare’s neck and mane.

The stallion performs “seeking thrusts,” followed by penetration. Strong intravaginal thrusts drive the stallion’s penis deep inside the mare. As ejaculation occurs, the stallion’s penis head flares, his hindquarters muscles show rhythmic contraction, and the tail moves up and down in a characteristic motion known as “flagging.”

Post-ejaculation, the stallion’s posture relaxes, causing him to droop (i.e., collapse) onto the mare and all thrusting behavior stops. After a few seconds of rest, the stallion dismounts (or falls off) the mare and begins the post-mating behaviors.

Mares lift their heads, spread their forelegs, and push backward to support the stallion’s weight and brace against his powerful thrusting.

Copulation is often accompanied by grunts and squeals from both the mare and stallion.

Post-Mating Behaviours Between Horses

Once the stallion dismounts, his flaccid penis is retracted into his sheath, and he sniffs the mare’s vagina and ground behind the mare. Spilled semen and expelled vaginal fluids will cause the stallion to exhibit a flehmen response.

The mare will contract her abdominal muscles and expel excess semen, preventing unhealthy fluid accumulation and reducing the risk of intravaginal bacterial infection. Experienced mares may also flirt with the stallion in an attempt to arouse him for continued mating.

During the refractory period, stallions show no interest in continued mating; however, the length of the refractory period varies between stallions.

Stallions with low libidos and little interest in mating leave the mare and rebuff any further attempts to mate. These stallions will ignore or even chase a persistently flirty mare.

However, high libido stallions will cover a receptive mare multiple times a day. Small breed stallions frequently have a higher libido than large draft breed stallions. Native pony stallions have been observed voluntarily covering a mare three times within one hour.

How Are Domestic Horses Mated?

Mating of domestic horses can occur under one of three conditions:

Natural pasture breeding
Natural in-hand breeding
Artificial breeding with fresh, chilled, or frozen semen

Natural Pasture Mating Between Horses

Natural pasture breeding is similar to the mating of wild horses. The stallion is either allowed to run with a herd of mares or introduced to new mares each breeding season.

The domestic mare and stallion mate without human interference or assistance. Natural pasture mating is often used for operations that breed the same stallion to a band of mares, year after year.

Due to the high injury risk when introducing a new mare to an established herd, these stallions’ books are closed and not open to outside mares.

The Pros And Cons Of Natural Pasture Mating Between Horses

The advantages of natural pasture mating are:

Lowers the mare and stallions stress levels during mating
Reduces the risk of handler injury
Increases the conception rate; many pasture-bred horses have a 100% conception rate as long as both the mare and stallion are healthy.

The disadvantages of natural pasture mating include:

It is difficult to know when the mare conceived, and thus owners struggle to plan for the arrival of the foal as the exact due date is unknown.
Mares are covered year after year without a break.
Introducing new mares to the stallion can result in costly injuries
A higher risk of sexually transmitted diseases being passed from mare to stallion
Other horses often interfere with the mating and may behave aggressively towards the mare being covered

Natural In-Hand Mating Between Horses

Natural in-hand breeding occurs when the stallion live covers a mare under the guidance and restraint of human handlers.

Before the in-hand covering, a mare is scanned for ovulation by a veterinarian or reproductive specialist. Some studs also use teaser stallions to check the mare’s receptivity to a stallion.

Once the mare is in full estrus and ready to stand, she is brought to the breeding shed, where the stallion covers her. Both the mare and stallion are fitted with protective equipment to protect them from injury. Mares may also be hobbled, twitched, or tied to prevent her kicking out at the stallion.

The stallion may be handled in a halter, regular bridle, or specialized stallion bit or chain. The stallion covers the mare once before being taken back to his paddock or stall.

The Pros And Cons Of Natural In-Hand Mating Between Horses

The advantages of in-hand natural covering include:

Knowing the exact date of conception and thus expected foaling date
Reducing the risk of mare or stallion injury when mating horses who are unfamiliar with each other
Allows the stallion to cover many more mares each year than is possible in the wild

The disadvantages of in-hand natural covering include:

Increased mare and stallion stress.
Increased risk of human handler injury; many people have been seriously injured when assisting an in-hand covering.
Stallions may show abnormal sexual behavior, e.g., uncharacteristically high aggression or depressed libido.
A higher risk of sexually transmitted diseases being passed from mare to stallion
Lower conception rate; live in-hand cover typically results in a 60% to 80% conception rate.

Artificial Mating Between Horses

Artificial breeding occurs when the stallion’s semen is collected and later used to inseminate the mare.

Artificial breeding can only be performed if the stallion is willing to mount a phantom mare for semen collection.

A teaser mare (preferably a mare in season) is used to excite the stallion. Once the stallion achieves an erection and shows mounting behavior, the stallion is encouraged to mount the phantom mare.

The phantom mare is a sturdy barrel-shaped structure that is heavily padded to prevent the stallion from injuring himself once mounted. Once mounted, the stallion thrusts into an artificial vagina, and the semen is collected.

A live jump mare may also be used. As the stallion mounts the jump mare, his penis is guided into a handheld artificial vagina rather than the mare. Phantom mares are preferred to live mares as the use of phantom mare reduces the risk of injury and improves hygiene.

The Pros And Cons Of Artificial Mating Between Horses

The advantages of artificial breeding include:

Reduced risk of stallion and human handler injury
No chance of mare injury
No risk of mare to stallion transmission of sexually transmitted diseases
Semen can be tested for disease (i.e., prevent stallion to mare transmission of disease), sperm count, sperm motility, and other predictors of fertility.
Each ejaculate can be divided into smaller volumes and used to impregnate multiple mares.
Deceased stallions or stallions living far away can be used to cover a mare if the semen is chilled or frozen.
Semen can be collected and stored during the off-season; competition stallions won’t be distracted or lose condition by covering mares.
The date of insemination and conception are known, and thus owners can calculate the exact foaling date.
Is commonly used in embryo transfer mares, where a surrogate mare carries the fertilized embryo of another mare.

The disadvantages of artificial breeding include:

It is costly
Lower conception rate, i.e., 50% to 70%
Mares have to be closely monitored for ovulation, and the risk of intravaginal infection is higher.
Some stallions cannot be trained to jump a phantom mare
Stallions may develop abnormal sexual behaviors with increased handler aggression, decreased libido, or inability to ejaculate

How Do You Know If A Mating Was Successful?

There are a few different methods that veterinarians and breeders use to determine if the mare is pregnant:

Observation
Blood tests
Rectal palpation
Ultrasonography

Observation As A Means Of Pregnancy Determination In Mares

Observation is one of the oldest means of determining if a mare is pregnant or not. On average, mares cycle every 21 days, mares who show no signs of a season 18 to 23 days after mating are more than likely pregnant.

However, this method of pregnancy determination is not full proof.

Some mares do not cycle regularly due to abnormalities with their reproductive systems, while others are known to have silent heats. Silent heats occur when mares come into season but show no external signs of being in estrus.

Mares with silent heats or reproductive issues may be mistakenly classified as pregnant and not returned to the stallion for a repeat breeding attempt.

A small percentage of mares appear to show signs of being in estrus even while pregnant; however, stallions are rarely interested in covering these mares.

Before the widespread use of ultrasounds in horses, some veterinarians would insert a sterile speculum into a mare’s vagina to check her cervix. A pregnant mare’s cervix should be tightly closed and slightly elongated, unlike the relaxed and somewhat open (soft) cervix of a mare in heat.

Can Blood Tests Show If The Mating Was Successful?

Three different blood tests can be used to determine if a mare is pregnant:

Progesterone levels after day 14 post-ovulation; this test can result in a false positive if the mare has elevated progesterone levels for a reason unrelated to her pregnancy status
Equine chorionic gonadotropin between 35- and 100-days post-ovulation
Estrogen spike after day 80 post-ovulation

Is Rectal Palpation Used To Check For Mare Pregnancy?

Not all veterinarians have access to a rectal ultrasound, and many continue to use the old-fashioned method of rectal palpation to determine if the mare is pregnant.

A few very skilled veterinarians can detect a mare’s pregnancy as early as 25 to 28 days post-ovulation via rectal palpation. At 30 to 35 days post-ovulation, the fertilized egg (conceptus) can be felt at the base of the uterine horn.

As the developing embryo grows and enlarges, it becomes easier to palpate it through the rectal and uterine walls.

Between days 85 and 120 days, the fetus can be felt as the structures surrounding the fetus relax and soften.

Can Mare’s Receive Ultrasounds?

Rectal ultrasonography is the gold standard for pregnancy detection in mares.

Important ultrasound dates include:

Day 14 to 16: pregnancy confirmation and check for twins
Day 26 to 30: check for fetal heartbeat and viability
Day 60: elective ultrasound to determine the fetus’ gender

Ultrasounds are the only method of pregnancy that allows the detection of twins. Multiple births place both the mare and unborn foals at serious risk of complications, including death. Current veterinary practices advise that one embryo be destroyed before day 17 if twins are detected.

When Are Mares Ready To Mate?

Both mares and stallions can only mate once they go through puberty and achieve sexual maturity. Most yearling fillies experience their first season between 15 to 18 months during their second spring.

Although, large breed horses like Clydesdales and Shires tend to reach sexual maturity later than small Native Pony Breeds, like Fell and Dale Ponies.

The filly’s physical condition also influences when she achieves sexual maturity. Fillies in excellent condition with access to good nutrition are likely to go through puberty earlier than fillies who are stunted and underweight.

Despite their first season occurring relatively early, it is rare for fillies, even wild fillies, to fall pregnant before 2yrs of age; only 0.9% of wild yearlings fall pregnant. 13.5% of free-ranging 2yr old fillies fall pregnant, but most wild fillies only reach peak fertility at 4 years or older.

Experienced sporthorse breeders delay breeding until the filly has finished growing, i.e., 3 to 5 yrs old. Sustaining a pregnancy is incredibly stressful on a female’s body and may stunt the filly’s growth as her body funnels valuable nutrients to the in-utero foal.

If the mare is later sold, her small size will negatively affect her market value.

In addition to this, many breeders feel that fillies who are bred too young are not mentally mature enough to mother a foal correctly.

It is a little like girls who fall pregnant in their early teens; their bodies are sexually mature enough to sustain their pregnancy, but they may not be physically, mentally, or emotionally mature enough to look after a baby 24/7!

When Are Stallions Ready To Mate?

Colts achieve sexual maturity earlier than fillies. Most colts begin producing viable sperm at 12 to 14 months, although it is rare for a colt to sire a foal before 15 months.

Despite this, the horse community is filled with stories of colts as young as 8 months siring foals on their female paddock mates; much to the owner’s chagrin, it is often the colt’s mother who falls pregnant! To avoid unwanted pregnancies, intact colts should be separated from mares and fillies after weaning.

As the colt matures, their testosterone levels, testis size, and sperm production increase resulting in increased fertility and more persistent sexual behavior; a stallion won’t reach peak fertility until after 4yrs old.

In the wild, dominant herd stallions chase colts away, preventing them from covering their mothers and sisters. The displaced colts typically form loose bachelor herds with other young colts, where they learn how to fight, play and develop into powerful young stallions.

The stiff competition between wild stallions limits the mating opportunities available to the young colts; most wild colts only sire foals after their third year.

The horse world is inundated with unwanted poorly bred horses, and thus most breeders prefer to wait until a stallion has proven himself as a competition horse before using him to breed to their mares.

Conclusion

Horse mating in the wild and natural pasture mating is characterized by three distinct phases; courtship, copulation, and post-mating behaviors.

In-hand covering often has an abbreviated courtship phase, and horses are prevented from displaying ritual post-mating behaviors.

Artificial breeding lacks all three phases of natural mating as the semen collection occurs at a different time and place than mare insemination. With artificial breeding, the risk of injury is minimized as the mare and stallion do not come in contact with each other.

How Do Horses Mate?