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Equine Production… All you need to know about artificial insemination and pregnancy diagnosis in your mare

Emma Seamark BVetMed (Hons) MRCVS, St David’s Equine Practice

In the previous article, we discussed what to consider when putting your mare in foal and the pre-breeding reproductive examination. In this article, we will discuss methods of artificial insemination and pregnancy diagnosis following insemination.

Artificial insemination has become an increasingly popular procedure for sports horse mares, compared to natural cover, due to both health and safety factors and the ability to breed without the need for travelling vast distances. For artificial insemination the semen is collected from the stallion, either chilled or frozen, transported to the required location and then inseminated into the mare.

Artificial Insemination – fresh, chilled or frozen semen?

Artificial insemination (AI) in horses can be carried out with fresh, chilled or frozen semen however the type of semen used is often dependent on various factors including mare management, timing of the insemination and availability of semen from the desired stallion. As insemination techniques have developed the rates of conception are often equal for chilled and good quality frozen semen.

Fresh semen

Fresh semen must be inseminated within 12 hours of collection from the required stallion before being chilled and so is only suitable to be used in mares that are resident on a stud or walk into stud daily.

Chilled semen

Chilled semen is commonly used for equine AI and is sent via courier overnight. Often, chilled semen can only be collected on certain days of the week by certain stallions and so it is essential that there is good communication between the mare owner, stud and vet to ensure that the semen is available at the adequate time. All chilled semen must arrive with the necessary paperwork prior to insemination

Frozen semen

The advantage of frozen semen over chilled semen is that breeders can use semen from stallions that are competing, based abroad or no longer alive. Frozen semen can also be sent well in advance of the date required and so can avoid the courier complications that sometimes arise with chilled semen.

Frozen semen has a short half-life once thawed so must be inseminated close to ovulation. This will require repeat ultrasound scans by your veterinary surgeon to ensure that insemination occurs at the correct time.

AI is best performed at the clinic as stocks are available which allow the mare to be safely positioned for scanning and insemination. This is not only safest for the vets when scanning but also reduces the risks of damage to the mare if she were to move. If it is not possible to bring the mare into the clinic then sedation is often required for scanning mares on yards without stocks. All mares undergoing AI with frozen semen need to be brought in to the clinic due to the frequent scanning required.


Mares are routinely scanned approximately 4-12 hours post insemination to monitor for evidence of excessive inflammation and fluid production in the uterus. If necessary then uterine lavage, antibiotics and oxytocin are administered at this stage.

The next stage is pregnancy diagnosis by ultrasound scan and this is advised at 14-16 days post ovulation. If the mare is confirmed in foal at this scan then it is advised that repeat ultrasound scans are carried out at 25 and 45 days to ensure that the pregnancy has been maintained.

Vaccinations for in-foal mares

It is always advised that in-foal mares are up to date with both Equine Influenza and Tetanus vaccinations, however we also advise in-foal mares are also vaccinated against Equine Herpes Virus (types I and IV) as this is known to cause abortion. Equine Herpes Virus vaccination is administered at 5, 7 and 9 months of gestation.

St David’s Equine Practice provides the equine veterinary services for Molecare Veterinary Services. Visit www.stdavids-equine.co.uk for more information.

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