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.

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.”

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.

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.”

• For unlimited access to advice on how best to care for your horse, subscribe to the Horse & Hound website

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Equine breeding season occurs in the spring and summer. It is during this time that mares go into recurring cycles of oestrus, giving a window of approximately five to seven days in roughly every 21 days in which a mare is “in season”.

Breeding a mare takes careful preparation and precision, with plenty to work out in advance. From choosing a stallion and selecting a broodmare to working out how much it costs to breed a horse, a healthy amount of research should go into your decision.

When are mares in season?

Mares are seasonally polyoestrus, which means they recurrently come into season at a particular time of year. Generally speaking, a mare’s breeding cycles take place between April and October. However, this – and cycle length – can vary horse to horse.

In winter, a mare’s reproductive system goes into a rest period, known as anoestrus. After this winter inactivity, the cycle usually begins again in spring.

The mare does not suddenly begin to cycle regularly, but has a “transitional phase” when the length is variable. Once the mare is truly in the breeding season, her oestrus cycles last around 21 days.

Equine breeding season – understanding the oestrus cycle

Most mares have a 21-day oestrous (breeding) cycle. This is divided into:

• Oestrus (average five to seven days)
• Dioestrus (14–16 days)

The cycles begin at puberty (approximately 18–24 months) and continue throughout the mare’s life.

Oestrus

During this time, the mare is receptive to the stallion. Typical signs of oestrus include:

• Adopting a urinating stance, raising the tail raised and uritinating in small squirts
• Opening and closing the vulval lips, known as “winking”

During this time one or more ovarian follicles enlarge and burst, releasing an egg. This is ovulation.

The mare normally ovulates approximately 24 hours before the end of oestrus, and its exact timing is only determined by performing ultrasound scans of the ovaries.

Dioestrus

The mare’s receptiveness ends and she may flatten her ears, swish her tail or squeal/kick out at the stallion.

How long is a mare pregnant for?

If breeding is successful, mares are pregnant for about 11 months, though a gestation period anywhere between 320 and 350 days is completely normal for horses.

Manipulating a mare’s breeding cycle

Factors such as daylight, nutrition and temperature influence the equine breeding season.

Daylight controls the production of hormones that trigger a mare’s cycling. Therefore, the natural breeding season in the mare is strongest from May until August, when the days are longest, and the weather is warmest.

During the spring, or the months of February to April, the weather is unpredictable and the daylight hours relatively few. This irregularity and limited daylight window creates variability in the mare.

At this time, it can be difficult to predict when the mare will ovulate. This makes is all the more tricky to determine an accurate time to cover or use artificial insemination (AI). Therefore, it is not cost-effective to breed her, whatever breeding method you choose.

During the early equine breeding season, it’s possible to artificially manipulate the mare to encourage normal cycling, which can shorten this uncertain transitional period. Vet use two main methods to do this.

Light

Studies have shown that artificially increasing daylight to 14–16 hours daily for a minimum of eight to 10 weeks can induce normal cycling.

Progestogens

Progesterone treatment suppresses the release of luteinising hormone (LH), which allows LH to build up and be stored.

When progesterone treatment is stopped, a surge in LH induces a strong oestrous which usually results in ovulation.

ReguMate (Altrenogest) given orally once daily for 10-15 days is commonly used during the transitional period. Mares come into season four to seven days later and ovulation occurs seven to 12 days after treatment has stopped.

Vets also use progesterone releasing devices, which are placed in the vagina for 10–12 days. These medicines are shown to encourage ovulation and result in more successful insemination.

• For unlimited access to advice on how best to care for your horse, subscribe to the Horse & Hound website

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The ethics around different breeding techniques – and how far is too far – have come under discussion by industry experts.

At the British Equine Veterinary Association (BEVA) Congress (13–16 September), in a debate chaired by former BEVA president Huw Griffiths, an expert panel discussed equine assisted reproductive techniques (ARTs), framed around the question “How far is too far?”. The aim was to explore which ARTs are “pushing the boundaries” in terms of animal welfare and social licence, and empower vets to have more evidence when advising a client if they do not believe it’s appropriate in certain cases to go ahead with a procedure.

World Horse Welfare chief executive Roly Owers opened the debate and said when thinking about how far is too far, vets need to consider ethics and welfare and that it is important to make sure everyone is “on the same page”. He referred to the BEVA panel discussion on what good welfare means, reported in H&H last week (news, 19 October).

Mr Owers highlighted the need to reflect on how efficient current breeding is for the horse sport market and discussed research published this year showing that within any given year, only around one-fifth of horses bred for sport will have a long-term career in equestrian sport; with the others withdrawing owing to reasons including lack of ability or injury.

“Maybe we should be thinking about how we can improve this system, before we breed more,” he said. “People often think it’s the large breeders that create all the problems, but that is not true – far more horses come from the individual breeder, breeding one animal at a time.”

Mr Owers concluded that some areas the industry needs to focus on are lack of research around ARTs, what plans have been made for a foal’s future, particularly if it does not fulfil its breeder’s expectations, whether pain involved with ARTs is assessed well enough and whether fertility clinics should be licenced.

Madeleine Campbell, who was an equine reproduction specialist prior to focusing on equine ethics and welfare, discussed the term “the yuck factor”, where consideration had to be given to society’s views on nature and ethics and whether using ARTs is “interfering more than humans ought to be”. She also mentioned looking at breeding holistically and giving consideration to the impact at breed, species, societal, and environmental levels.

“Breeding is ethically different from any other veterinary intervention, other than blood collection. The reason is that we do this thing to the horse, whatever it may be, without the expectation that we are going to improve the horse’s health by doing it,” she said.

“Every other veterinary intervention we do, we are trying to improve the health of an animal. And it’s not any one animal we’re talking about – we’ve got a mare and a stallion, we’ve often got recipient mares involved. And it’s not only one generation – we’re talking about future animals.

“As we start to move towards the possibility of genetic editing of embryos in a commercial setting, then we open up the option that we will permanently alter something for all future animals from that one onwards, so ethically that is a big thing to be thinking about.”

Veterinary reproduction specialists Camilla Scott, Tom Stout and Emma Lorenzen presented different cases involving the use of ARTs, such as ovum pick-up (OPU – where oocytes are aspirated from the mare’s ovary) and intra-cytoplasm sperm injections (ICSI – where a single sperm is injected through the outer surface of a mature oocyte) and talked about the success rates and benefits. In one example, a top showjumping mare had died, and using ICSI, oocytes were recovered and a foal was bred who went on to become a successful licensed stallion.

The complications associated with the procedures in different horses – including pain – were also discussed, and when ARTs are appropriate or not. It was agreed across the board that pain control during ART procedures needs to be a major focus.

One attendee said he believed there were two sides to the use of ARTs.

“One is how can we exercise these various techniques while keeping the discomfort to a minimum? The second is how do we communicate to the public to keep our social licence?” they said. “I think social licence varies a lot based on the level of knowledge about the technique. It seems that the less people know about a particular technique, the more important the ‘yuck factor’ becomes.”

The overpopulation of horses was also discussed, in terms of horses who do not stay sound and end up unwanted. And one attendee highlighted the benefits of ARTs where horses can be bred who are healthier and more specifically targeted for a purpose.

Professor Campbell said it is not just the responsibility of vets to consider breeding decisions and the use of ARTs, but also breeders.

“Breeders need to not be aiming to produce horses that look amazing when they are four, but are then crippled when they are eight,” she said, adding that there is a need to have more data and to track horses bred via ARTs to record if they develop any health problems later in life.

In conclusion, it was agreed that group discussions on ARTs and breeding are “vital” and should be ongoing to maintain trust across the industry and with the public.

“It’s good to build up the evidence base. We need to start building our own guidelines and regulating ourselves, if we don’t then it’s our own fault when other people step in and try to regulate us,” Professor Stout.

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Subscribe to Horse & Hound magazine today – and enjoy unlimited website access all year round

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Stay in touch with all the news in the run-up to and throughout the major shows and events during 2026 and beyond with a Horse & Hound subscription. Subscribe today for all you need to know ahead of these major events, plus online reports on the action as it happens from our expert team of reporters and in-depth analysis in our special commemorative magazines. Have a subscription already? Set up your unlimited website access now

Embryo transfer in horses is a type of assisted reproductive technology that has now become commonplace in equine breeding.

Embryo transfer (ET) is a means of surrogacy; it involves removing, or flushing, an embryo from the uterus of the biological dam, and implanting it into the uterus of a recipient mare, who will then carry the pregnancy to term.

Equine embryo transfer: the process

ET is used in conjunction with artificial insemination (AI), and the “donor” mare is inseminated with fresh, chilled or frozen semen. Six to eight days after ovulation, the embryo will be flushed from the mare’s uterus. this is a simple, non-surgical procedure, that involves flushing the uterus with a special fluid, which is then drained. The embryo is isolated and then transferred into the uterus of the recipient mare using a catheter inserted through the cervix.

A key aspect of ET is the synchronisation of the recipient mare. Ultrasound scanning and use of hormone injections/implants are used to ensure that she ovulates as close in time to the donor mare as possible, meaning her uterus will be ready to receive the embryo at the right time.

The recipient mare will be scanned around a week later to make sure she is pregnant, and she will then carry the pregnancy as normal. She will deliver the foal and nurse it until weaning.

What are the advantages of using embryo transfer?

ET was first developed in the 1970s, and its primary purpose in the early years was to enable the breeding of older mares, or those with problems carrying a foal to term.

These days, it is still used for older mares, but more commonly for breeding from high-quality competition mares, without interrupting their sporting schedule, and with the potential to obtain more than one foal per year from the same mare. It also enables quality mares who, for whatever reason cannot safely or successfully carry a foal, to pass on their genes.

What is the success rate of embryo transfer in horses?

The success rate of ET depends on many of the same factors that a normal pregnancy would, primarily the fertility of the stallion and dam, the quality of the semen and the timing of insemination. In young, healthy mares, and where the synchronisation and ET procedure itself has been expertly carried out, the typical embryo recovery rate is around 75-80%. Overall, ET typically has a success rate of around 60-65% per cycle. It is common for two or three cycles to be required before a successful pregnancy is achieved.

How much does embryo transfer cost?

The costs involved in ET vary and primarily depend on how many cycles are required, the type of semen that is used (fresh, chilled or frozen) and whether or not a recipient mare needs to be hired.

You can expect to pay anywhere between £275 and £450+ VAT per cycle for a veterinary AI package – using frozen semen usually costs more than fresh or chilled – plus a synchronisation fee of around £275+VAT, a flushing fee of around £290+VAT and a transfer fee of around £185+VAT. Two or more potential recipient mares are usually required, to maximise the chances of successful synchronisation.

If you need to hire a recipient mare, expect to pay £2000+VAT from conception until weaning.

Things like scans, examinations, semen fees and keep for the recipient mare also need to be factored in to the overall cost of breeding a horse.

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Subscribe to Horse & Hound magazine today – and enjoy unlimited website access all year round

Horse & Hound magazine, out every Thursday, is packed with all the latest news and reports, as well as interviews, specials, nostalgia, vet and training advice. Find how you can enjoy the magazine delivered to your door every week, plus options to upgrade your subscription to access our online service that brings you breaking news and reports as well as other benefits.

Stay in touch with all the news in the run-up to and throughout the major shows and events during 2026 and beyond with a Horse & Hound subscription. Subscribe today for all you need to know ahead of these major events, plus online reports on the action as it happens from our expert team of reporters and in-depth analysis in our special commemorative magazines. Have a subscription already? Set up your unlimited website access now

If you’re planning artificial insemination (AI) for your mare, how can you maximise your chances of success? Andrea Oakes identifies the most important points to consider

If you’re planning using 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.

1. Logistical planning

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 equine vet and breeding specialist Emma Houghton MRCVS. “She is then out of season (in dioestrus), for 14-15 days.”

Timing plays a vital role in successful artificial insemination (AI). The point of ovulation can be manipulated to enable insemination of semen at the optimum moment, according to its type (see below).

“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.”

2. Semen type for artificial insemination in horses

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 is longest-lasting once inseminated. It must usually be used within three hours, but this varies between stallions.

➤ Chilled: next best fertility-wise, chilled semen has been 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 modern extenders and veterinary management. It can be stored ready for use and opens up a worldwide pool of stallions, but the considerable veterinary input required 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.

“Our breeding season coincides with several bank holidays,” says Fred Barrelet, a stud medicine specialist at Rossdales Veterinary Surgeons, adding that weekends and postal or courier failures can scupper plans to inseminate inside a critical timeframe.

“Semen should have been processed at an EU-approved collection centre and must be accompanied by the original veterinary health certificate. It is illegal to use semen from an unknown source or imported from abroad without the required health documentation.”

3. Mare preparation

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 contagious equine metritis (CEM), equine viral arteritis (EVA), equine infectious anaemia (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, and 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 when and how she was bred, 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.”

4. Stallion fertility for artificial insemination

His looks, performance and temperament may tick all the right boxes, but will your chosen stallion’s semen get your mare in foal?

Relevant fertility data can be hard to obtain, warns Fred.

“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%.

“My advice with a young, maiden mare at the start of the season is to invest in semen from a top stallion. Most sport horses have a career behind them, however, so you may be breeding from a middle-aged lady. As with many species, the chances of getting a mare pregnant drop off with age.

“If she is older than 14 and barren [was not covered/failed to conceive the last breeding season], don’t use the most expensive stallion or frozen semen. Your chances of getting her pregnant more efficiently will probably be better the following year, once her fertility is proven and she has foaled without complications.”

5. Where to carry out artificial insemination in horses

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 when potential stress is minimised,” says Emma. “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.”

6. Artificial insemination in horses: potential pitfalls

It sounds so simple — and often it is — yet AI can disappoint the unwary.

“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 and is lost. 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.”

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Equine frozen embryos are cropping up more and more in the world of sport horse breeding. Embryo transfer, and the sale of embryos already implanted in a recipient mare, has been around for a few years, but now, with scientific processes allowing for more effective and reliable freezing and thawing of equine embryos, more buyers and breeders are exploring the possibility.

Equine frozen embryos: how does it work?

An embryo is the result of a successful fertilisation of a female egg by a male sperm cell. This embryo is then flushed from the mare (if fertilisation does not take place via ICSI) and can be frozen using vitrification, a method of rapid cryopreservation. The embryo can then be preserved in liquid nitrogen to be stored or transported, and transferred into a recipient mare at a later date.

Advantages of frozen embryos

The possibility to freeze and transport embryos offers a convenient way to buy and breed horses, as well as preserving and making available valuable genetics. It allows breeders to delay the implantation of the embryo into a recipient mare to a date of their choosing, for example if embryos are flushed from the donor mare in autumn, then can be frozen, stored and implanted early the following spring.

It also allows for easier import and export of embryos, as it eliminates the need to transport a mare carrying a live embryo, thus opening up a much larger market for the trading of embryos.

The opportunities they offer

Embryo auctions are not new, but frozen embryos are appearing more and more in catalogues of major auctions such as Zangersheide and Ekestrian. The growth of the online auction, partly accelerated by the pandemic, has expanded the market further, allowing embryos to be bought easily from anywhere in the world.

But auctions are not the only means of purchasing a high-quality frozen embryo. The launch of Mares of Macha (MoM), by Belgian entrepreneur Klaas de Coster, alongside Belgian Olympic bronze medal-winning showjumper Pieter Devos, has given breeders the chance to select and purchase frozen embryos from top quality damlines. Under the tagline “Access proven breeding”, MoM offers frozen embryos from their roster of top-class mares for sale online at set prices, moving away from the competitive bidding nature of an auction.

“We noticed that it was difficult to access the best bloodlines – the most common way to do this was via auctions where only the highest bidder could get an exclusive foal. To make this easier, we had to do something different,” says Pieter. “We try to find the best mares in the world and offer all the embryos for fixed and accessible prices on our website.”

Current prices range from €7,750 for a Baloubet Du Rouet embryo out of Vibelle Z up to €25,000 for a Heartbreaker embryo out of Olympic mare Sancha LS. MoM also offers an optional “no pregnancy, no pay” warranty, and under this will arrange for implantation as well as transportation of the embryo.

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Horse & Hound magazine, out every Thursday, is packed with all the latest news and reports, as well as interviews, specials, nostalgia, vet and training advice. Find how you can enjoy the magazine delivered to your door every week, plus options to upgrade your subscription to access our online service that brings you breaking news and reports as well as other benefits.

Stay in touch with all the news in the run-up to and throughout the major shows and events during 2026 and beyond with a Horse & Hound subscription. Subscribe today for all you need to know ahead of these major events, plus online reports on the action as it happens from our expert team of reporters and in-depth analysis in our special commemorative magazines. Have a subscription already? Set up your unlimited website access now

Modern reproductive methods may offer a better chance of breeding success, but what do the abbreviations mean – and which is right for your mare? Dr Charles Cooke MRCVS explains

Breeding has always been based on decisions, from which stallion to use to the method of breeding and where to foal the mare. Recently, these decisions have become more numerous, with the emergence of a range of modern assisted reproductive technologies.

Careful planning remains a must, whichever method is chosen, so that you and your vet can maximise the chances of success. Certain questions still need to be asked beforehand. Is the mare healthy? Does she have any conditions that might prevent her from carrying the pregnancy and foaling? Consideration must also be given to when you want the foal to be born, and the logistics of using your chosen stallion.

You may also wonder if you can still breed from your mare while she is competing, or whether it will take several years for her to produce the multiple foals you are hoping for. While much will depend upon your mare’s age, health and breeding history, assisted reproductive technologies may broaden your options, as long as you are not intending to breed a racehorse as natural cover remains the requirement in the thoroughbred racing industry.

Modern assisted reproductive technologies offer solutions for sport horse and pony breeders, and benefits to the horseworld in general. They allow us to ensure the welfare of breeding horses, by using surrogates when a mare cannot carry her own foal, and preserve bloodlines to maintain a wide genetic pool, supporting the recovery of rare breeds.

Technology can also help to preserve the genes of stallions that would otherwise be lost. When a stallion has been critically injured, becomes ill or dies, it is possible to harvest and freeze semen using a process called epididymal sperm extraction. This technique can also be used after a stallion has been castrated.

Mare preparation

Any breeding process requires the mare to be managed with care. This usually involves pre-breeding health tests, including a swab for contagious equine metritis (CEM) and blood samples for equine viral arteritis (EVA) and equine infectious anemia (EIA), along with an understanding of her reproductive cycle.

For most mares, there is a transition from the winter quiescent (inactive) state to a regular 21-day oestrus cycle in March/April, in response to increasing daylight hours. Part of the pre-breeding assessment is to check where the mare is in her cycle, so she can be bred at precisely the right time.

The safety of the mare, handler and vet is paramount, so using stocks and occasionally sedation for examination is advisable.

Artificial insemination (AI)

Artificial insemination (AI), the most commonly used assisted reproductive technology in equine breeding, involves a series of ultrasound examinations and medications to ensure the mare is inseminated close to ovulation (pictured, above). Fresh semen must be used within three hours, but it can also be supplied chilled or frozen. Your choice will dictate how the mare is managed.

Chilled semen is viable for 24 to 48 hours after collection, so must be ordered and couriered following careful monitoring of the mare. Ovulatory drugs help to ensure the follicle ovulates – releases a mature egg – within the correct time frame.

Frozen semen must be stored appropriately (pictured, above right) and can be used when needed over a time period of many years. Increased veterinary input is needed with frozen semen, to time the insemination for the best pregnancy rates. The aim is to inseminate the mare within six to eight hours of ovulation, so repeated ultrasounds, possibly overnight, are required.

Frozen semen doses vary from a single 0.5ml straw to the more usual four to eight straws. The use of the deep intrauterine insemination (DUI) technique is essential for a lower volume, to deposit the sperm at the tip of the uterus – next to the Fallopian tube – where the oocyte (egg) will be waiting.

With appropriate veterinary management before and after insemination, pregnancy rates for chilled and frozen AI are similar – which increases stallion choice.

Advantages: AI opens up a worldwide stallion market. However, if you are considering a non-UK stallion, it is advisable to use an experienced semen agent, due to the new Brexit regulations.

Embryo transfer (ET)

Embryo transfer (ET) involves inseminating a donor mare, then “flushing” her uterus seven to eight days later to collect the embryo. This is transferred into the uterus of the recipient, or surrogate, mare who then carries the pregnancy.

The reproductive cycles of the donor and recipient must be synchronised, so that the embryo remains in similar conditions. It is recommended that two or more synchronised recipients are ready, to ensure the “best fit” with the donor mare at the time of transfer. However, you don’t necessarily need your own recipient mares, as the embryo can be chilled and couriered promptly to a mare at another location.

Advantages: ET can be repeated multiple times during the season, increasing the number of foals a mare can produce per year. It is worth considering for a competition mare, to avoid interrupting her career, or for a mare with fertility issues or an injury that would prevent her from carrying her own pregnancy.

Intracytoplasmic sperm injection (ICSI)

Intracytoplasmic sperm injection (ICSI) is used in conjunction with Ovum pick-up (below). In this lab-based technique, a single sperm is injected into the matured oocyte, which is held in specialised fluid medium and incubated to encourage the development of an embryo. This can take up to nine days.

Not all of the oocytes will develop into an embryo, but those that do can be transferred immediately into recipient mares or frozen for future use.

Advantages: ICSI is an efficient way of using semen, as a single straw can be used multiple times. The technique is advantageous for sub-fertile stallions or where semen stocks are limited, perhaps because a stallion has died.

OVUM pick-up (OPU)

OVUM pick-up (OPU) is the collection of oocytes from the ovarian follicles of the mare.

The collection process is performed with the mare standing, under sedation with epidural anaesthesia. An internal ultrasound probe is used to visualise the ovary, so that a guided needle can then aspirate (draw) the fluid and oocyte from the follicle. The process continues until 15 to 20 follicles have been aspirated.

The fluid is examined under a microscope. The tiny oocytes are collected, processed and incubated to allow them to mature. Suitable ones are fertilised by intracytoplasmic sperm injections, and the resulting embryo is transferred into a recipient mare.

While OPU is a more involved technique, it is generally well tolerated by the mare and can be repeated in three to four weeks, as long as sufficient follicles develop. It can also be performed outside the usual breeding season. Embryos can then be frozen and stored, exported internationally, or thawed to allow foals to be born at a particular time of the year.

Advantages: OPU is useful for mares with fertility problems – for example, those unable to conceive, maintain or carry a pregnancy, or where ET has been unsuccessful or is not appropriate. As a single-day procedure, involving minimal medication, it is ideal for the busy competition mare.

Meet the veterinary expert

DR CHARLES COOKE is a Royal College of Veterinary Surgeons advanced practitioner in equine stud medicine and a director at Equine Reproductive Services (UK), a North Yorkshire-based first-opinion and referral practice offering specialist advice to vets and owners. With a passion for all aspects of equine reproduction and fertility, Charles deals with a varied caseload of thoroughbred, sport and leisure horses.01653 668190, equinereproductiveservices.co.uk

Also published in H&H 11 March 2021

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Find out more about breeding

Embryo transfer (ET) allows competition mares to keep performing while passing on their genes to the next generation.

One of the major advantages is being able to breed more than once from a mare in one breeding season. It is quite usual for two different stallions to be selected and the ET process carried out twice, enabling one mare to produce two foals by two different stallions.

ET involves the transfer of an embryo from a mare who has been covered to a recipient. It is important that the recipient mare is at a similar stage in her cycle (ideally one to two days behind the donor mare) to ensure that the embryo is being placed into a receptive environment.

Research has shown that the optimum time to perform the transfer is when the embryo

is eight days old.

It is removed from the donor mare by flushing a sterile solution into the uterus; this fluid is then siphoned back out of the uterus and passed through a fine filter, which catches the embryo.

The embryo is then inserted through the cervix into the uterus of the recipient mare.

The international average for embryo recovery is 50%. There is an overall success rate of 40% per embryo flush.

For the full embryo transfer diary, see the current issue of Horse & Hound (2 June, 2011)

Read more about breeding

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Inseminating mares with chilled semen is a common method of reproduction, allowing owners to keep their mare at home and increasing the range of stallions available.

The aim of breeding using chilled semen has always been to inseminate the mare just before ovulation (when the mare’s egg is released).

But occasionally mares do not ovulate as expected or there may be problems with the courier service transporting the semen.

As a result, it has previously been thought that, because of a high incidence of both pregnancy failure and infection associated with inseminating the sperm after ovulation, the only option was to miss this breeding cycle and wait for the whole process of lining the mare up for insemination to start again. This was both costly and time-consuming.

Vets from a big breeding practice in the UK looked at the breeding records of over 150 mares inseminated with chilled semen.

They found that, contrary to opinion, good pregnancy rates with acceptable pregnancy losses can result from insemination with chilled semen within 16 hours of ovulation.

They did note that it was important the mare’s uterus was treated with saline flushing and an infusion of antibiotics after insemination to reduce the risk of her developing an infection.

Repeated administration of the reproductive hormone oxytocin was also given until the uterus appeared free from fluid.

This is extremely useful for all mare owners and vets working with chilled semen as it means we can often successfully inseminate the mare to obtain a viable pregnancy, even if the semen arrives late.

For the full veterinary article on what’s new in breeding, see the current issue of Horse & Hound (13 January, 2011)

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When choosing a stallion for artificial insemination, finding out about their fertility is vital, but this is sometimes easier said than done.

Fertility results are hard to obtain for chilled or frozen semen from sport horse stallions in the UK.

For thoroughbreds conceived naturally, this data is available in the comprehensive annual Weatherbys’ statistical review, but, in many cases, the same information is not available for semen from stallions being used in an artificial insemination programme in the UK.

Is the semen fit for purpose?

It is a good idea to make enquiries about the level of experience of the stud or AI centre responsible for collecting semen.

As part of this you should ask about the health status of the stallion. This refers to tests that are undertaken to ensure his semen will not pass on venereal diseases such as equine viral arteritis, contagious equine metritis and other bacterial venereal diseases.

If originating from outside the UK, each shipment of semen is legally required to contain official health papers certifying the semen is free from these diseases.

Is the semen good quality?

There can never be a guarantee that any particular semen sample will result in a pregnancy, but as a mare owner you have a right to receive a semen sample when you ask for it, with correct health papers and of sufficient quality to enable a pregnancy in your mare.

One good way to obtain data about the quality of the semen shipped out is to ask the stallion owner or semen shipping centre if they can let you speak directly to any broodmare owners who have used their services.

Six questions to ask when choosing a stallion for artificial insemination:

• What are the stallion’s fertility results?

• Is the AI centre competent?

• Does he have health papers that you can view?

• How will the semen be packaged and transported?

• How many doses (for chilled semen) or straws (for frozen semen) will you receive and what are the terms of using them?

• Are there any restrictions on dates for semen collection?

For the full article on choosing a stallion for artificial insemination, see the current issue of Horse & Hound (11 February, ’10)

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Anne Brown from Gadebrook Stud gives first-hand experience of the DEFRA-approved course which qualifies breeders to artificially inseminate their own mares

Since DEFRA relaxed the strict rules governing insemination of mares in 2004, laymen can train as artificial insemination (AI) technicians on an approved course, and practise insemination if they pass the qualifying exam.

For many reasons, stallion and broodmare owners often prefer artificial insemination (AI). It is usually safer and more hygienic than live covering. It enables a working stallion to keep competing and it cuts out the need for a mare with a young foal at foot to travel to a stud. The semen can be collected to order and delivered in a purpose-made container.

However, until recently, there was an extra cost to pay for the insemination, a procedure previously limited to qualified vets, although stallion owners have always been able to collect semen without restriction.

The course

The course lasted two days and was organised by the British Equine Veterinary Association (BEVA) and approved by DEFRA.

The fee for the lectures and practical seminars was £395, including excellent meals at the Hare and Hounds Hotel at Westonbirt, in the Cotswolds. Accommodation for two nights added another £160.

The location was chosen for its proximity to the Willesley Equine Clinic, run by Chris Shepherd MRCVS and his team, the base for most of the practical sessions.

An impressive line-up of vets representing some of the most experienced and respected practices in the country greeted us for the first morning’s lectures.

Chris started introductions with AI expert Martin Boyle MRCVS from Stallion Reproduction Services in Cambridge. Next was John Gilliver MRCVS from Lancashire, then Jonathan Pycock MRCVS from Equine Reproductive Services in Yorkshire. Last but not least was Tessa Clarke, not a vet but someone who probably does more stallion collections than the rest put together at her West Kington Stud, an AI centre near Chippenham.

Most members of the group of three men and 17 women had some experience of stud work. Some were vet students, and one dairy farmer was already adept at inseminating bull semen into the much trickier uterine tract of cows.

Our syllabus included the relevant anatomy of mare and stallion, learning how to collect, evaluate and package semen with extender to prolong its viability and how to prepare a mare for insemination.

We learned how to complete the paperwork to keep accurate records, how to set up the ideal AI unit with three separate areas for preparation, collection, and a lab for subsequent microscopic examination, and how to ensure the necessary health checks for mare and stallion before the breeding season begins.

Hands-on experience

Hands-on experience allowed us to explore the insides of docile mares and watch semen collection from a novice Shadwell Stud Arab racehorse stallion.

The artificial vagina (AV) plays an all-important part in collection, as each stallion needs a slightly different size and temperature for successful ejaculation. Finding out what suits individual stallions will ensure better results.

Knowing which and how much extender to add to the semen for transportation to the mare owner is another ingredient of this complex process. Speed is of the essence, but the semen must be kept cool during transportation to the mare to save it “burning out”.

Chris Shepherd took us to his Willesley Clinic for the practical insemination session, preceded by a useful hands-on gynaecological inspection of post-mortem uterine tracts. This was vital in understanding the physiology of the organs and the location of the ovaries, Fallopian tubes and oviducts, allowing us to know exactly how and where to insert the catheter without risk of damage to the mare.

Then we got to the heart of all we were learning. In the stocks, a patient chestnut mare, tail bandaged, rear end cleaned and dried off, allowed five sets of exploratory forefingers, then fists, to fumble through her reproductive passages to locate the entry to the cervix.

Then each student nervously introduced the plastic catheter the required distance into the uterus, eased with non-spermicidal jelly. Fixing the two-part syringe full of semen to the end of the catheter required a third helper, illustrating the need for teamwork in such a delicate operation.

Semen collection and examination

The insemination practical even overshadowed the more dramatic task of collecting semen from Jiyush by one of our students, Alexander Peternell, who had first prepared the AV with the required amount of 50°F water in sterile conditions, then allowed it to cool to around 24-28°F.

Alexander gently introduced the AV on to the stallion, redirecting the flow of semen from the mare (who was wearing kicking boots) to the largest condom any of us had ever seen — an extra-strong rubber glove produced in France.

The semen was then rushed back to the lab at Willesley for us to examine under a microscope for volume, progressively motile sperm (usually well in excess of a billion per ejaculate), and concentration. From this, we learnt how to calculate the sperm count.

All vets stressed “best practice” throughout and referred to the Horserace Betting Levy Board codes on sexually transmitted diseases such as CEM, Equine Viral Arteritis (EVA) and Equine Herpes Virus (EHV).

A final written exam sorted out the candidates. To date, more than 240 students — including me — have qualified as AI Technicians and received their DEFRA exemption allowing them to inseminate mares. Liability insurance would be essential for commercial practitioners planning to inseminate mares belonging to other people.

The two abiding lessons of the course, apart from the clinical training, were the importance of cleanliness and meticulous record-keeping, to protect both stallion and mare owner.

The course qualifies those who pass the exam to inseminate mares in the UK with fresh and chilled semen. Using frozen semen from overseas-based stallions is a much more complex operation. It needs skill to identify the follicle’s optimum moment for insemination, involving a rectal ultrasound, and this procedure is forbidden to all but qualified vets.

This veterinary feature was first published in Horse & Hound (13 April ’06)

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Artificial insemination, or AI, is becoming increasingly commonplace. Although there is a code of practice — produced by the British Equine Veterinary Association (BEVA) — AI is unregulated by the government, so the whole system relies, to a great extent, on owners’ compliance and trust.

Although the code of practice is available to all, many owners may not be fully conversant with the content or how to get it, and struggle to piece together the pros and cons when considering AI. As the process grows in popularity, so the options available need proper consideration.

“I cringe when owners think it’s a cheaper alternative to natural breeding,” says equine breeding expert vet Dr Jonathan Pycock. “It requires a high degree of technical input and can quite often end up more expensive than natural covering.”

Any broodmare being prepared for AI needs to be monitored carefully. Insemination needs to take place when she is close to ovulating, at the end of her season, so it’s useful to know her cycle pattern before you start any AI programme.

If you are considering using AI for your mare, check with your vet that they are experienced in the procedure, and if not, ask if they can refer you to another practice for advice. (BEVA holds a list of practices with a special interest in AI.)

Reasons to use artificial insemination

• If the stallion is competing, the breeding season would interrupt his schedule
• The stallion is abroad or too far away to make natural covering viable
• A stallion has died but semen was frozen for use after his death
• A gelding has performed well and semen was frozen prior to castration
• To obtain better/different bloodlines for a rare breed — and to encourage its geographical spread

Frozen or chilled semen

Sometimes only frozen semen will be available, but if there is a choice, AI expert vet Chris Shepherd from Willesley Equine Clinic advises that chilled is best.

“By choice, we would always work with chilled semen because the examination times aren’t so stringent and conception rates are slightly higher,” he says. “With frozen semen, we aim to inseminate within 6hr of ovulation, so the timing is critical and requires a lot of monitoring, which can be quite onerous. We charge more for frozen semen.”

How the semen will be delivered can cause problems. Often the delivery is sent with a conventional courier, who will not deliver on Saturday, Sunday or bank holidays, so two days of a mare’s season may effectively be “lost”. Frozen semen can be stored by your vet, but chilled must be sent as your mare is ready to inseminate.

“With only Monday-Friday delivery, if the mare needs inseminating at the weekend it’s virtually impossible to get semen from abroad,” says Chris Shepherd. “I don’t know if we’ll ever get round that — even within the UK it’s difficult, unless the mare owner is prepared to get in the car and drive frantically to collect it, which most are. One of the advantages of frozen semen is that you can get it on site well ahead of the mare.”

Potential problems

AI with chilled or frozen semen generally has a lower success rate than natural covering. So as well as deciding on the right stallion, there are several ways of improving the chances of success. Use good-quality semen, an experienced vet and a fertile mare, and results can be almost as good as with natural covering.

Although AI increases the choice of stallions, it also brings with it a risk of disease, particularly Equine Viral Arteritis (EVA). EVA is a viral venereal disease and there is much concern that it may enter this country in semen imported for AI, so it is important to ensure your mare or stallion is clear.

“EVA is much more prevalent in mainland Europe than the UK — which is attempting to maintain a disease-free status,” explains Dr Pycock. “Were the disease to enter the UK, the effects would potentially be devastating, as the horse population would be very susceptible to its effects.”

• For a copy of BEVA’s code of practice or a list of recommended vet practices, e-mail info@beva.org.uk, visit: www.beva.org.uk or tel: 01223 636970

This article was first published in Horse & Hound

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For those of us involved in the equine breeding industry, it is obvious that artificial insemination (AI) is set to play an ever-increasing role in the future. One of these areas of growth will be in the technique of deep uterine insemination (DUI) when using frozen semen.

Conventionally, mares are inseminated with a minimum of 500 million progressively motile (live) sperm. This is known as the insemination dose.

The semen is infused via a catheter into the middle of the mare’s uterus (womb). The uterus is T-shaped, and is made up of a first part called the body and two horns (left and right). Once the semen has been put into the uterus, the sperm travel up one of the horns until they reach the tip. There, they arrive at the entrance to the oviduct or uterine (fallopian) tube.

Once sperm have passed through this junction and are in the oviduct, they can fuse with and fertilise the female oocyte or egg. Very few sperm from the millions inseminated make it up the uterine horn and into the oviduct.

The ovaries, one on each side, are situated close to the opening of the oviducts. When ovulation occurs, an egg is released, usually from only one of the ovaries, and begins to travel down the oviduct towards the uterus. Veterinary examination, especially ultrasound scans, will detect the enlarging follicle and enable a confident prediction to be made as to which side ovulation will occur and when, so that insemination can maximise the chance of fertilisation.

Current thinking is that the number of sperm reaching the oviduct may be between 100 and 1,000. Once this was discovered, researchers investigated how few sperm may be necessary to achieve fertilisation when placed directly at the tip of the uterine horn during insemination. This interest stemmed from the increase in use of frozen semen. Semen from some stallions is notoriously difficult to freeze or in very short supply and it would be of tremendous benefit if mares could become pregnant as a result of inseminating much lower doses of sperm.

This is called “low dose insemination”, and since the sperm are inseminated much further into the uterus than with conventional AI, the other term used to describe it is “deep uterine insemination” or DUI.

There are two methods for inseminating the sperm deep into the uterus. The first is to use a special catheter (long plastic tube), which is guided up the uterine horn by placing one hand in the rectum of the mare and slowly advancing the catheter.

The second method is to place an endoscope in the uterus and actually see the tip of the uterine horn. The semen can then be inseminated via a special catheter inserted down the endoscope.

Using a rectally-guided catheter

The mare should be prepared for DUI in a clean, well-lit environment; stocks for restraint are essential.

A special catheter is used. This is long enough to reach the tip of the uterine horn while still having one end protruding externally. The catheters have a rounded tip at the end, so that they can be advanced up the uterine horn without catching on the folds that line the uterus. It is very important that the catheter reaches into the uterine body and does not remain obstructed in the cervix.

This passage through the cervix is not always easy. By rectal palpation, the vet can feel the catheter within the uterus and guide it deeper into the uterus than can normally be achieved. The catheter should be gently pushed until the tip is at the very tip of the uterine horn. This is where the sperm should be deposited. Using this technique, satisfactory pregnancy rates have been achieved with sperm numbers of 50 to 100 million.

Using an endoscope

Endoscopes are long, flexible tubes with a bright light source at the end. They allow internal structures to be viewed and are commonly used in an examination of the horse’s respiratory tract.

It is possible to place an endoscope into the uterus of a mare through the vagina and cervix in much the same way as an insemination catheter. Air is then passed through a channel in the endoscope into the uterus, which allows the inside of the mare’s reproductive tract to be seen.

The operator can gently steer the tip of the endoscope up the uterus until the entrance of the oviduct (fallopian tube) is reached. A special narrow catheter can be passed down a central channel within the endoscope, and the tip of the catheter exposed beyond the end so it can be seen. By careful steering of the tip of the endoscope, the catheter can be placed very close to the entrance of the oviduct.

Semen is then blown out of the catheter directly on to the surface of the papilla. Using this technique, acceptable pregnancy rates can be achieved using as few as five million sperm. This represents a hundredfold decrease in the usual number needed.

By depositing the sperm so close to the site of fertilisation, the distance they need to travel is reduced. In addition, the exposure to the potentially hostile uterine environment is reduced. These are the two most likely reasons sperm numbers can be so drastically reduced.

The future

The implications of DUI for the equine breeding industry need to be evaluated carefully. A theoretical concern is that this reduces the natural selection process by which only the “fittest” sperm travelling the whole way on their own succeed in fertilising the egg.

Obviously, using a catheter to carry out DUI is much easier and cheaper than using an endoscope. In our practice, we routinely inseminate mares with frozen semen using the DUI technique by catheter. If the client wishes us to reduce the number of straws of semen used or the semen is in very short supply, we will use an endoscope.

This veterinary feature was first published in Horse&Hound (28 April, ’05)

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Artificial insemination (AI) has been used regularly in horse breeding since the beginning of the 20th century. There are some restrictions on the use of AI, most notably from the General Stud Book, which regulates the thoroughbred.

AI involves two key processes:

• The collection, evaluation and dilution of semen from the stallion
• The well-timed infusion of sperm into the mare’s uterus

Sperm must be thoroughly examined to make sure that it is of sufficient quality to be used in an AI programme. It must also be processed properly to ensure that it retains its fertilising potential.

AI in the horse is technically difficult and not cheap. Many mare owners expect the costs to be less for AI since the mare does not have to go to stud – but there can be considerable costs involved.

The overall pregnancy rates at the end of the season vary between 50% and 90%, with an average of around 75%-80%. Some mares lose the pregnancy and the live foal rate is around 70%.

Pros and cons of artificial insemination

Advantages include:

• Eliminates cost and stress of transporting a mare and perhaps her foal
• Greater number of mares can be inseminated
• An increased choice of stallions, particularly from abroad
• The mare’s owner can retain control over the management of the mare and foal
• Regular semen evaluation
• Extenders with proper antibiotics helps preserve the longevity of sperm and minimises bacterial contamination
• AI reduces the risk of sexually transmissible diseases spreading throughout a breeding population or between farms, as long as the correct procedures are followed.

Disadvantages include:

• Higher costs
• Strict regulations to prevent the control of diseases
• Need for adequate infrastructure in order to transport the semen
• Semen from some stallions will not tolerate the cooling and/or the freezing and thawing process
• Lack of appropriately trained and skilled vets

The role of the vet in equine AI is crucial, although appropriately trained “AI technicians” can perform the insemination of the mare only a vet can perform the necessary checks to ensure the mare is ready.

Frozen semen

Advantages include:

• Semen can be transported easily internationally
• Semen can be used from competing or injured stallions
• Semen from potentially valuable stallions can be frozen and stored indefinitely

Disadvantages include:

• Pregnancy rates are often disappointing
• Charges for freezing stallion spermatozoa are relatively high
• Thawed frozen semen has a short life span
• Frequent veterinary examinations are necessary

Breeding assessment for mares

Mares should have a thorough pre-breeding assessment before breeding via AI, this should include a complete breeding history of the mare for the past five years and the following should be considered:

• Age: fertility declines once a mare is over 10 years old
• Previous breeding history

Accurate prediction of ovulation is important because the best time for AI with chilled semen is in the 24hr leading up to ovulation. Pregnancy rates will generally fall if insemination is outside this range. This time interval is shorter than if fresh semen or natural mating is used, and the window of opportunity is even shorter with frozen semen.

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