Artificial insemination in horses with essential information for owners

Artificial insemination in horses is a technically demanding but routine part of modern equine veterinary practice. It is a modern breeding technique that can be incredibly complex and requires accuracy and strict biosecurity, plus good timing and organisation to be successful. In the UK, it sits firmly within the professional responsibilities outlined by the Royal College of Veterinary Surgeons (RCVS).

If you’re planning to use artificial insemination (AI) for your mare this breeding season, how can you maximise the chances of a successful equine pregnancy? We outline the most important points to consider when using artificial insemination in horses and explain what’s involved in the process.

How is artificial insemination done in horses?

Routinely, the process is as follows…

1. Semen collection

This begins with appropriate preparation of the stallion and the environment. In well-managed studs, stallions are trained to mount a phantom (dummy) mare rather than a live mare. This significantly reduces risk to both animals and handlers. An artificial vagina (AV) is carefully prepared to replicate physiological conditions – specifically temperature, pressure, and lubrication – so that ejaculation occurs in a controlled and humane manner.

The veterinary surgeon, or suitably trained personnel under direction, must handle the stallion in a way that minimises stress and risk of injury. Hygiene is critical: the AV must be sterile or single-use lined. In addition, collection vessels must be clean and pre-warmed. Obvious contaminants, such as dirt or urine, must be avoided.

Poor technique here can compromise semen quality and ultimately fertility outcomes.

2. Semen evaluation and handling

Once collected, semen is assessed promptly and properly. This directly informs clinical decisions about whether the ejaculate is suitable for use and how it should be processed.

Evaluation typically includes motility (movement), concentration, and morphology (assessing size and shape). This is all carried out under controlled temperature conditions to avoid cold shock. Accuracy in terms of process and record-keeping is essential.

3. Extension and preparation

To preserve sperm viability and produce multiple doses, semen is diluted with an appropriate extender following evaluation. Extenders are designed to buffer pH, provide energy substrates, and reduce bacterial growth.

Controlled temperature conditions are essential to dilution. Abrupt changes can irreversibly damage sperm membranes. Again, traceability and documentation are important, particularly where transporting semen between premises.

4. Storage and transport

If semen is not used immediately, it may be cooled for short-term storage or frozen for long-term preservation.

5. Insemination and post-breeding care

Your vet will manually insert the semen at the optimum time using a pipette. The mare is typically scanned via ultrasound 24–48 hours post-insemination to ensure ovulation has occurred and to check for any fluid buildup in the uterus. A second ultrasound scan is performed 14–16 days after breeding to confirm conception.

Horse being artificially inseminated by vet

There are various benefits of AI being carried out at a dedicated breeding centre. Credit: Peter Nixon

Can AI be carried out at home?

AI can be carried out at home, at an equine clinic or at a specialist breeding centre. So what might influence your choice?

“Studies show that pregnancy rates improve with minimised potential stress,” says equine vet and breeding expert Emma Cooper MRCVS. “Certain horses may be more relaxed at home, but you will ideally need stocks for ultrasound scanning and insemination.”

Insemination with frozen semen is particularly difficult to carry out at home, yet fresh and chilled also need a vet’s input.

“An AI package at a stud or clinic could well prove cheaper, as driving and visit fees often add up to more,” says Emma. “The benefit of a clinic is that the vet can examine a mare as often as necessary without the owner having to be there.

“Every mare is different, but an experienced repro vet with knowledge of AI will be able to see more detail in the uterus and follicle to tell exactly where she is in her cycle. Better care will most likely bring a better result – and fewer scans could lower costs.”

Bay mare grazing with her foal stood side-on next to her. the foal has a star and two white socks

Vets recommend turning your mare out with another who has a similarly-aged foal. Photo: Alamy

Pros and cons of artificial insemination in horses

It sounds so simple – and often it is – yet AI can disappoint the unwary. Take a look below at its pros and cons in summary:

Advantages

Reduced risk of injury to mare and stallion
Access to geographically distant or elite stallions
Allows use of chilled or frozen semen (genetic flexibility)
Better disease control (no direct contact)
Precise timing with ovulation → often good conception rates

Disadvantages

Requires veterinary expertise and monitoring (costly)
Variable fertility with frozen semen
Not permitted in some studbooks (e.g. Weatherbys/The Jockey Club for thoroughbreds)
Handling/storage logistics for semen

How much does AI cost?

Artificial insemination in horses can incur rapidly mounting costs, which you will need to add to the other costs of breeding a horse.

Pre-breeding assessment

Vets recommend a thorough pre-breeding check, which should include a complete gynaecological assessment, including ultrasound and appropriate tests for infections that can affect fertility (such as a blood test for equine viral arteritis and a swab for contagious equine metritis) as well as a general health check, including a worm egg count.

The mare’s vaccinations should also be up to date.

This is likely to cost between £215–300, including VAT, and is vitally important.

Cost of insemination

Costs for insemination can vary hugely depending on what clinical costs include. However, in addition to the cost of semen, you should be budgeting:

Chilled semen package = at least £525, including two pregnancy scans (including VAT)
Frozen semen package = at least £625, including two pregnancy scans (including VAT)

There are many potential additional costs, such as sedation, treatment for infection or infertility, such as uterine lavages and other additional treatments.

In other cases, the mares will be straightforward, and the costs may be less.

Be wary of additional charges

“Make sure you know the costs up front,” says Emma. “Ask if stud or clinic prices include extras such as livery, drugs and pregnancy scans, and whether you’ll pay the same the second time around if your mare does not conceive on the first cycle.

“Most AIs are fine, but complications can occur. Not all mares cycle every 21 days. Others produce excessive uterine fluid so that when the embryo enters the uterus it cannot survive.

“There’s also a reasonably high rate of twinning with some mares. The uterus is typically not large enough to sustain both embryos. While there’s a high success rate if one is ‘squeezed’ within the appropriate time, this does involve a risk to the other one.

“We don’t always know of potential problems until we start looking.”

Consider that a healthy foal, or that the foal will mature into a quality horse, is not a given. As such, careful consideration is essential from the outset.

What is the success rate of artificial insemination in horses?

Conformation, temperament, size, soundness and freedom from hereditary conditions – all these will influence your choice of stallion. But will your chosen stallion’s semen get your mare in foal?

You also want to obtain a fertility record from the stud manager. That said, relevant fertility data can be hard to obtain, warns Fred Barrelet, a Newmarket reproduction vet.

“The key measure of a stallion’s fertility is his per-cycle conception rate, but many stud owners don’t publish this,” he says. “The number of mares he gets into foal tells you nothing about the time taken. What you need to know is the breeding efficiency achieved with his semen.

“Ask the stallion owner, stud or semen vendor for the number of mares that become pregnant per cycle. A lot depends on management and the individual mare, but you need to hear an answer of about 50%.”

Semen quality/handling, timing and the standard of clinical management also affect success, although no single variable determines outcome. Rather, the pregnancy rate reflects how well these elements align.

Mare selection

Younger mares generally have higher conception rates. With advancing age, there is a higher incidence of degenerative changes within the uterus. Such changes mean that after breeding, fluid and inflammatory debris do not clear as well, resulting in an increased chance of persistent uterine infections.

This is one of the most common causes of subfertility.

In addition, the cervix of older mares may not relax as effectively during oestrus, which can hinder both semen deposition and uterine clearance.

Egg quality also declines with age, so even when fertilisation occurs, early embryonic loss is more likely. So clinically, this means older mares often require more intensive management.

Semen types: what are your options?

A good semen sample will contain billions of sperm, but which type is best for your mare?

Fresh: straight from the stallion (who must be on-site or nearby), fresh semen offers the highest fertility rates and lasts longest once inseminated. Its lifespan is usually three hours from collection, but this varies between stallions.
Chilled: next best fertility-wise. Chilled semen is mixed with extenders, preservatives and antibiotics to lengthen its lifespan to up to 30 hours. This enables insemination at home and widens stallion choice to further afield in the UK, or even Europe. Timing is still an issue: it must be ready at the premises prior to your mare ovulating.
Frozen: fertility rates associated with frozen semen have improved with the use of extenders and veterinary management. It can be stored ready for use and opens up a worldwide pool of stallions. However, it requires considerable veterinary input, and can push up costs (insemination must take place within six hours prior to, and four hours after ovulation). Sperm from certain stallions has better post-thaw motility – swimming ability – than others.

Semen choice will largely depend upon your mare’s age and breeding health. Fresh or chilled will maximise an older mare’s chances of conceiving – provided it arrives on time, prior to ovulation.

Mare ready for artificial insemination assessment

Mares are assessed using ultrasound throughout the process. Credit: Jon Stroud Media

Getting the timing right

During the horse breeding season, a mare ovulates (releases an egg) every 18-24 days – a process called cycling. Each egg forms inside the ovary in a structure known as a follicle.

“A mare is in season – or oestrus – for four to seven days, although this can vary from two to 12 days,” says Emma. “She is then out of season (in dioestrus), for 14-15 days.”

Timing and logistics therefore play a crucial role in successful AI.

“The stud team must work within a relatively narrow biological window as to when the mare is going to ovulate working with perishable materials,” adds Emma.

“It can be harder than one might think to predict ovulation and select the best time to inseminate a mare. Each mare is individual and reproductive cycles will vary. Therefore, veterinary teams must monitor her frequently and diligently monitoring using ultrasound, particularly when breeding from older mares.”

Vets can manipulate the point of ovulation to enable insemination of semen at the optimum moment, according to its type.

“During a season, follicle growth goes hand-in-hand with an increase in the oedema [fluid] within the mare’s uterus,” explains Emma. “When the follicle reaches a key size of 35mm we can use either one of two ovulation-inducing drugs, Chorulon and Ovuplant.

“The mare should then ovulate within 24-48 hours, which gives us a window to order and inseminate semen prior to ovulation. Follicle size may be smaller, though, particularly in ponies, so it helps to know a mare’s breeding history.”

Health is key

According to the British Equestrian Veterinary Association (BEVA), due to the serious concern of the spread of infectious diseases, it is best practice to only accept semen from a stallion for AI tested for contagious equine metritis (CEM), equine viral arteritis (EVA) and equine infectious anaemia (EIA) after 1 January 2026.

Generally, vets request that this certification arrive with the semen at delivery, otherwise they will be unable to proceed with insemination. This is already mandatory for all EU/foreign stallions – it is illegal to use semen from an unknown source or imported from abroad without the required health documentation.

It is wise to request this certification for UK stallions as well.

How do I prepare my mare for artificial insemination?

Good general health is essential for a mum-to-be, so keep your mare’s vaccination and worming programmes up to date and her hooves and teeth well maintained.

But how else can you prepare her for AI?

“We’d rather see a mare too light than too heavy, so aim for fair condition,” says Edward Matson of Twemlows Stud Farm and AI/ET (embryo transfer) centre. “Like females of all species, horses are more likely to conceive on a rising plane of nutrition.”

If you’re sending your mare to a stud or clinic for AI, pre-entry health requirements could include checks for CEM, EVA, EIA and strangles.

Edward points out that pre-breeding examinations are not always definitive in predicting a mare’s chances of conceiving.

“It is difficult to assess a maiden [first-time] mare’s reproductive health before she comes into season,” he says. “A specialised equine repro vet might suggest endometrial swabs or more complex biopsies with a potential problem mare.

“Around 80% of problems occur once the semen is inserted in the uterus, however. You can’t tell too much till then.

“If your mare has foaled previously, give the vet as much information as you can about her breeding history. This should include her own breeding information, the type of semen used and the cycle she conceived on – or why she didn’t. This can save a lot of time and money.

“Be realistic with an older maiden mare. She may be super-fertile or she may not, but you won’t know until you try.”