Artificial Insemination (AI)

The health and safety benefits of artificial insemination (AI) are well recognised. When semen is of good quality and the mare is managed and inseminated at the appropriate time, conception rates using fresh, chilled or frozen semen can compare favourably with those achieved through natural covering.

Artificial insemination involves collecting semen from a stallion and placing it directly into the mare’s uterus at the optimum point in her oestrous cycle. The management of the mare and timing of insemination will depend on whether fresh, chilled or frozen semen is being used.

Preparing the mare for Artificial Insemination

Before beginning an AI programme, the mare should undergo a pre-breeding gynaecological examination to assess her reproductive health and suitability for breeding.

Testing requirements will vary according to the mare’s history, the stallion stud’s conditions and current disease-control guidance. These may include clitoral or endometrial swabs for contagious equine metritis (CEM) and blood testing for infectious diseases such as equine viral arteritis (EVA).

An endometrial swab, cytology or low-volume uterine lavage may also be recommended to assess the uterine environment and identify evidence of inflammation or infection.

The mare’s follicular activity will be monitored closely using ultrasound examinations, alongside other indicators of her reproductive cycle. Once a suitable follicle has developed and the mare is approaching ovulation, medication may be administered to induce or more accurately time ovulation.

The timing of induction and insemination will depend on:

  • The type of semen being used

  • The expected longevity of the semen

  • The mare’s stage of cycle

  • The ovulation-inducing medication selected

  • Collection and delivery arrangements

For fresh or chilled semen, the aim is generally to inseminate the mare before ovulation. Many breeding programmes aim for insemination within the preceding 24 hours, although semen longevity varies between stallions and according to how it has been processed and stored.

Benefits of Artificial Insemination

Artificial insemination offers several potential advantages:

  • A reduced risk of disease transmission when appropriate screening and hygiene protocols are followed

  • A reduced risk of injury to the mare, stallion and personnel

  • Access to a wider selection of stallions in the UK and overseas

  • The potential to use semen from stallions that are competing, retired or deceased

  • The opportunity to assess semen quality before insemination

  • More efficient use of each ejaculate, as multiple doses may be prepared depending on semen quality and concentration

  • No requirement to transport the mare to the stallion

  • Reduced physical demands on the stallion

  • The ability for competing stallions to continue their sporting careers during the breeding season

Semen types

Fresh semen

Fresh semen is collected from the stallion and used promptly, with little or no preservation. The stallion and mare will therefore usually need to be at the same location, or close enough for the semen to reach the mare without delay.

When handled correctly and inseminated at the appropriate time, fresh semen generally offers good sperm longevity and conception rates.

Chilled semen

Chilled semen is mixed with a specialist extender, which supports and protects the sperm cells during storage and transport. It is then cooled gradually and transported in an insulated, lightproof container at approximately 5°C.

Chilled semen should ideally be inseminated within 24 hours of collection, although some samples may remain suitable for 24–48 hours or longer. Its quality and longevity vary between stallions.

Successful use of chilled semen requires good communication between the mare owner, attending vet and stallion stud. Collection and delivery must be coordinated carefully so that the semen arrives when the mare is ready to be inseminated.

Chilled semen can provide access to stallions throughout the UK and Europe without requiring the mare to travel. It also generally requires less intensive monitoring than frozen semen.

Fresh or chilled semen checklist

Before ordering fresh or chilled semen, consider the following:

  • Does the stallion’s semen chill and travel well?

  • On which days is the stallion available for collection?

  • When and how will the semen be dispatched?

  • How much notice does the stallion stud require?

  • How many insemination doses are included?

  • Are collection and transport costs included in the price?

  • What happens if the mare is not ready when the semen arrives?

  • What are the stallion stud’s disease-testing requirements?

  • Will imported semen be accompanied by the correct health certification and documentation?

Semen arriving from overseas must be transported and accompanied by the appropriate certification in accordance with current import requirements.

Frozen semen

Frozen semen is processed, divided into labelled straws and stored in liquid nitrogen at approximately −196°C. When stored and handled correctly, it can remain viable for many years.

The semen must be thawed carefully using the protocol provided by the collection centre or supplier. Because frozen-thawed sperm cells often have a shorter lifespan within the mare’s reproductive tract, insemination must be timed very close to ovulation.

This requires more intensive monitoring than fresh or chilled semen. After ovulation has been induced, the mare may need to be scanned approximately every six to eight hours so that ovulation can be identified and insemination performed at the optimum time.

The exact insemination protocol will depend on the semen’s quality, the number and type of straws available and the supplier’s instructions.

Benefits of frozen semen

The main advantages include:

  • It can be stored for many years

  • It offers access to stallions based overseas

  • It enables the use of semen from stallions that are still competing

  • It may allow breeding from retired or deceased stallions

  • It can be transported and stored ahead of the mare’s cycle, reducing reliance on last-minute collection and delivery

Frozen semen checklist

Before purchasing frozen semen:

  • Make sure it is being supplied by a reputable stud or agent

  • Ask for details of its quality, including post-thaw motility and previous pregnancy rates

  • Check how many doses and straws are included in the price

  • Confirm whether storage and transport costs are included

  • Request the supplier’s thawing and insemination instructions

  • Confirm where the semen will be stored before use

  • Ensure the transport container and liquid nitrogen levels are managed correctly

  • Check that imported semen has the appropriate health certification and documentation

  • Clarify what will happen to any unused straws after the mare is confirmed in foal

Is frozen semen suitable for every mare?

Many mares are suitable candidates for insemination with frozen semen, but it may not be the most appropriate option in every case.

Older mares and those with a history of reduced fertility, uterine fluid accumulation or post-breeding inflammation may have lower conception rates and require additional treatment. Frozen semen is therefore not always the first choice for mares over 16 years of age, although suitability should be assessed individually rather than by age alone.

Older maiden mares may also have reduced conception rates, but every case is different. A pre-breeding reproductive assessment can help identify potential concerns before semen is purchased.

Because frozen semen requires frequent ultrasound examinations, mares that strongly resent gynaecological procedures may be less suitable candidates. In some circumstances, examinations can be performed under sedation, provided this is considered safe and appropriate.

If you are unsure whether frozen semen is suitable for your mare, we will be happy to discuss her age, breeding history, temperament and reproductive health with you.

Post-insemination care

Following insemination, the mare will be examined to confirm ovulation and check for post-breeding inflammation or fluid within the uterus.

Treatment may be required, particularly in older mares or those with a history of delayed uterine clearance or breeding-induced endometritis. This may include:

  • Uterine lavage

  • Oxytocin administration

  • Other medication or supportive treatment appropriate to the individual mare

Some mares may require additional hormonal support during early pregnancy. This will only be recommended following veterinary assessment and where clinically appropriate.

Pregnancy diagnosis

The first pregnancy scan is generally performed 14–16 days after ovulation, rather than after the date of insemination. This early examination allows us to:

  • Confirm whether the mare is pregnant

  • Identify twin conceptuses

  • Arrange further assessment or treatment if required

  • Prepare for another breeding cycle if the mare is not in foal

We strongly recommend a further scan at approximately 28 days after ovulation to check for an embryonic heartbeat.

Another examination at around 42 days can confirm that the pregnancy is continuing normally. Further pregnancy scans and monitoring can then be discussed according to the mare’s individual circumstances.

If you need advice about artificial insemination or would like to discuss the most suitable type of semen for your mare, please do not hesitate to contact us.

A stud service tailored to you and your horse

Every breeding programme is different. We take the time to understand your mare or stallion, previous breeding history, intended timescales and breeding goals before recommending an appropriate plan.

From routine reproductive examinations and pregnancy diagnosis to fertility investigations and emergency mare and foal care, our experienced stud vet provides knowledgeable and personal veterinary support for breeders and horse owners across Suffolk and Essex.

To discuss routine stud work or arrange a reproductive examination, please contact our team