For the mare owner considering breeding from a mare, the decision of whether to proceed with natural cover vs. A.I. will depend on several factors. These may include:

• The availability of the stallion: Many sports horse stallions will only be available by A.I. due to competition commitments or concerns about the stallion suffering injury during covering.


• The age and breeding history of the mare: A.I. is particularly suitable for mares with lower fertility that are difficult to get in foal. These may include older mares or mares with poor vulval conformation which are prone to uterine infection (endometritis).


• The location of the stallion: A mare may go to a stud close to home and the semen can be brought in from elsewhere in the UK or abroad. This removes the need to subject the mare to long-distance travel and allows her to return home between ultrasound scans, insemination and pregnancy diagnosis, if desired.

Artificial insemination has several advantages over natural cover. These include:

• Mares may be bred to a stallion many miles away or abroad, without the need to transport them vast distances.


• There is a lower risk of uterine infection (post-breeding endometritis), which is the most common cause of low fertility.


• Mares may be bred with frozen semen from a stallion which has since died.


• It is considerably safer for the mare, stallion and the handlers.

A.I. may be performed with fresh, chilled or frozen semen. The choice is often governed by the availability of the desired stallion. Historically, conception rates have been highest with fresh semen, followed by chilled then frozen semen. As insemination techniques have developed, however, the use of good quality frozen semen in fertile mares frequently produces conception rates to equal fresh/chilled A.I.

• Suitable when the stallion undergoes semen collection at Ashbrook, or is located no more than 2 hours away.
• Particularly recommended for sub-fertile mares.

• Often available from stallions in other parts of the UK or Continental Europe.
• The semen is usually couriered to Ashbrook overnight.

• The semen is collected at stud and frozen in liquid nitrogen where it lasts indefinitely.
• Suitable for stallions located Worldwide.
• Suitable for competition stallions which may only be available for breeding/semen collection for a limited period.
• We routinely use a ‘deep intra-uterine’ insemination technique to deposit the semen at the very tip of the uterine horn.

In the Northern Hemisphere, the natural equine breeding season is May to October, although this may be manipulated by various methods to start the mare cycling earlier in the year. At Ashbrook, most mares are inseminated April to August. Mares come into season on average every 21 days, with the oestrus period (‘heat’ or ‘season’) lasting 4-7 days. Mares ovulate (release an ovum or ‘egg’) towards the end of the season. The timing of insemination relative to ovulation is critical to the success of A.I. and it is essential that mares are closely monitored by ultrasound scanning during this time. The gestation length is on average 11 months, although this can vary tremendously.

Before joining the A.I. programme at Ashbrook, mares must have a clitoral swab taken for Contagious Equine Metritis (CEM) and blood sample taken for Equine Viral Arteritis (EVA) in accordance with HBLB and BEVA Codes of Practice.

• Mares initially undergo an examination to assess their suitability for breeding and identify any conditions that may impair fertility e.g. uterine infection.
• When the mare is in season she is admitted to Ashbrook for daily or every other day scanning to detect the optimum time for insemination. Depending on whether the semen is fresh, chilled or frozen, insemination is performed shortly before or after ovulation.
• Mares are routinely scanned 4-12 hours post-insemination to check for evidence of excessive inflammation (post-breeding endometritis). Uterine lavage with sterile saline is performed to remove any dead sperm and inflammatory cells from the uterus. The live sperm are in the fallopian tubes (oviducts) at this stage and are not washed out or damaged by this procedure.
• Antibiotics may be infused into the uterus and oxytocin injections administered to encourage the uterus to contract and expel residual fluid.
• Most mares are discharged 24-36 hours after insemination.

An ultrasound scan is performed at Ashbrook 14 days after ovulation. If in foal, follow-up scans at 24 and 44 days are recommended to check the pregnancy is progressing normally.

In addition to routine vaccinations against Equine Influenza and Tetanus, we recommend that pregnant mares are vaccinated against Equine Herpes Virus (Types I and IV), which is known to cause abortion. Vaccination is performed at 5, 7 and 9 months of gestation.