Artificial Insemination in Horses

Courtnee Morton, DVM
By Courtnee Morton, DVM on Mar. 24, 2023
Mare and foal

What Is Artificial Insemination in Horses?

Artificial insemination (AI) in horses has become a popular breeding technique, as it allows horse breeders to improve the genetic quality of their herd without the risks of natural breeding. AI in horses involves the collection, preservation, and transfer of semen from a stallion to a mare. AI is helpful when a particular stallion may live far away from the mare, or when a mare has been difficult to impregnate. The AI process allows for more control in the breeding of a mare than natural “live cover,” or pasture breeding.

Collection and Preservation of Equine Semen

The collection of semen from stallions is typically done using an artificial vagina (AV), which mimics the natural reproductive process. The stallion is trained to mount a dummy mare, and the AV is used to collect the semen. Once collected, the semen is analyzed for motility (capable of movement), concentration, and morphology (biological form). These statistics are helpful to determine viability for fresh, cooled semen for immediate insemination, versus the freezing process for long-term preservation.

To preserve the sperm, it is diluted with an extender, which is a solution that contains nutrients and protective agents. The extender helps to maintain the viability of the sperm during storage and transportation. The diluted semen is then packaged in straws or vials. Depending on the method of preservation, semen will be shipped either on ice for fresh cooled specimen, or with liquid nitrogen for frozen samples. The thawing and use of semen is a delicate process; temperature variations can be deadly to sensitive sperm.

Timeline of Artificial Insemination in Horses

When deciding to breed your mare, the first decision is to select a stallion. Once a stud has been found, a contract is signed between stallion and mare owners; stallions typically only have certain “bookings” open per year and have a collection schedule. This will help veterinarians know how to plan when ordering semen depending on the mare’s likely time of ovulation and expected arrival of semen.

Fresh semen is used for local mares or can be shipped overnight to horses all over the country, which opens the possibilities for optimum breeding choices for mare owners. Frozen semen is typically sent to the veterinarian at the beginning of the breeding season so it can be kept on hand and ready for use at any time.  

AI via frozen and cooled semen also have different techniques. When using fresh semen, the ideal window for insemination is within 24 hours before a mare ovulates. The projected time of ovulation can be predicted as follicle development is monitored by repeated ultrasound evaluations by your veterinarian. Depending on the selected stallion’s collection schedule, and duration of travel (typically by end of day, or next day depending on distance), semen will be ordered the day before or day of suspected ovulation.

If a mare has a follicle that is likely to ovulate soon, the veterinarian may also administer a hormone such as Desorelin to help a mare ovulate within a certain window, if all signs point to impending ovulation. When using frozen semen, the ideal window for insemination is within six hours after the mare ovulates. When the mare is getting close to ovulating, your veterinarian will likely perform ultrasound exams every four to six hours until they see that a follicle has ovulated.

Preparing Mares for Insemination

At the appropriate time, the mare will be prepared for insemination by having her tail wrapped and cleaned thoroughly using a gentle soap such as Ivory. Depending on the insemination technique being used, your veterinarian may manually empty the rectum of manure before cleaning, so the AI pipette can be gently guided from above to ensure proper pipette placement. The goal of preparation is to minimize chances of hair, fecal, or bacterial contamination into the uterus; this is a sterile process. The gentle soap is recommended over a typical chlorhexidine or betadine scrub, as those can be deadly to semen.

Semen Transfer to Mares

Once the mare has been prepared, the semen will be thawed if frozen using specific instructions sent with the sample.

If cooled semen is being used, it will be kept in its box until the last possible moment, as light can also be harmful. Your veterinarian will put on a sterile palpation sleeve and apply sterile lubrication. A sterile pipette will be opened and will be gently passed through the vulva, cervix, into the uterus. Often, this is the place of semen deposit for cooled semen, unless a mare has been difficult to impregnate in the past or the semen has a low motility rate. In such cases, or when using frozen semen, a deep horn insemination technique is often used. This will involve leaving the tip of the pipette in the uterus, then pulling the palpating arm out before going into the rectum, so the veterinarian can feel the uterus horns and help gently guide the pipette with both hands. One directing the pipette from the outside and the other from the inside so the tip of the pipette is directed towards the ovary that is ovulating, getting the sperm as close as possible to where the egg will be.

After insemination, your veterinarian may recommend the use of oxytocin to help with uterine clearance, or the practice of before- and after-breeding uterine flushes. These are typically used in cases when a mare does not typically clear her edema/fluid  after ovulation; this increases the chance of a uterine infection or severe inflammation, which decreases the rate of pregnancy. Semen often causes an inflammatory reaction in the mare’s uterus. If she has a history of thickened uterine walls, repeat abortions, or infection after breeding, she may be a candidate for one of these procedures during the AI process.

What Is the Success Rate of Artificial Insemination in Horses?

The success rates of AI in horses can vary depending on several factors, such as the quality of the semen, the timing of insemination, and the reproductive health of the mare. On average, success rates for AI in horses range from 50%–70%. Frozen semen tends to have a lower success rate than cooled semen.

Possible reasons for lower success of AI include:

  • Poor motility or morphology of sperm

  • Delayed transport of sperm

  • Poor uterine health (thickening or other concerns, often diagnosed during a breeding soundness exam upon biopsy and culture)

  • Improper timing of insemination regarding ovulation

  • Reproductive status or history of a mare

    • When was the last time she foaled?

    • Is she a young maiden mare, or has she had multiple foals?

  • Older mares who have never had a foal before often have a harder time conceiving and maintaining a full-length pregnancy

The best conditions for AI success include:

  • Healthy uterus and sperm with good motility (pre- and post-shipping) and morphology

  • AI done in correct window for type of semen being used

  • Hormone assistance for ovulation timing and/or uterine clearance after breeding

  • Pre- or post-uterine lavage as needed

  • Luck!

It is important to remember, both for yourself and for the sake of veterinarians, that mares are not machines. Even if all the conditions are met correctly, this does not guarantee success for pregnancy. If you decide to breed your mare, it is important to be prepared both mentally and financially for the likelihood that things will not work out the first, second, or even third cycle of attempt. Sometimes things are also out your veterinarian’s control, and changes may need to be made including type of semen used, stallion used, or repeat diagnostics of your mare’s uterus to ensure that they are a strong candidate for breeding.

Is Artificial Insemination Better for Horses?

AI has many potential benefits for horses, including mare safety and transportation considerations.
Intact stallions breeding via live cover can be potentially dangerous for all involved—both the horses and their handlers. If a mare is not quite ready to be bred yet, she may reject the stallion which can involve squealing and kicking; and stallions in the heat of the moment often forget their manners. Helmets are important for handlers as the stallion often flings his hooves out when trying to mount the mare, and both horses can decide to kick. The act of breeding can also cause trauma to the mare’s reproductive tract occasionally, and stallions often bite or create wounds on the mare’s side.

While AI may have slightly lower success rates in comparison to live cover, the safety considerations are considerable, and it is much easier to ship semen overnight than having to ship your mare to potentially another state to reside there during the breeding season until success has been achieved.

What Are the Disadvantages of Artificial Insemination in Horses?

One of the largest disadvantages of AI vs. live covering your mare with a nearby stallion is the cost. Fees for breeding AI include the breeding contract, veterinary exams, shipping fees for semen, along with any surprise complications or repeat fees if things don’t go according to plan. Common obstacles include issues discussed above, along with unforeseen shipping delays or issues, missed ovulations, and not making “the list” in time on day of collection (each semen collection only makes a set number of doses, which is shipped on a “first come, first serve” basis).

Featured Image:

Courtnee Morton, DVM


Courtnee Morton, DVM


Dr. Courtnee Morton is a 2017 Ross University School of Veterinary Medicine graduate. Since graduation, she completed an equine internship...

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