Artificial Insemination in the Horse
By Dr. Paula Valeria

Artificial insemination, or AI, although still not allowed in some breed registries, is a large part of the equine breeding industry and is set to take on an increasing presence in the future.  AI in the horse requires a great degree of veterinary involvement and is not a cheep alternative to natural breeding.  

There are numerous advantages of AI with fresh cooled or frozen semen.  However, there are also disadvantages and it is important to look at both to be thoroughly prepared.  

Advantages include the following:

• Ability to breed multiple mares with a single ejaculate.
• Decreased stress and exposure to disease for mares (and foals) due to transport.
• Minimizing the risk of bacterial infections and sexually transmitted diseases.
• Ability for mares to breed to stallions anywhere in the country.
• Continued evaluation of semen so that problems with fertility can be caught earlier and better monitored.

Disadvantages include:

• Higher costs due to the technology and skill needed to collect, evaluate and ship semen.
• Mare must be evaluated to determine the stage of her cycle in order to time the insemination.
• Mare must be AI’d closer to ovulation than with live cover.
• Semen from some stallions does not tolerate the cooling or freezing and thawing process.

A successful AI program depends on both the stallion and the mare. Good communication between stallion and mare owners and their veterinarians is critical.  The semen sample must be collected, evaluated to make sure it is of adequate quality, processed to make sure it retains its fertilization potential when it reaches the mare, and then must be infused at the appropriate time of the mare’s cycle.

Stallion considerations
For the stallion this involves a thorough breeding soundness exam, ensuring that the semen is of adequate quality, and proper cooling and storage of the semen. 

Most stallions when trained will collect artificially using an AV (artificial vagina) and a breeding phantom or jump mare.  A stallion with normal libido will ejaculate in response to the appropriate pressure, temperature and friction.  The collected sample is then evaluated to get sperm concentration, look for abnormalities of the sperm and to determine motility.

Type of semen preservation depends upon length of time from collection until insemination. Undiluted semen needs to be used within 10min.  If it is put into a pre-warmed extender and kept out of the light in an air-tight container, it can stay at room temperature if used within 6-8 hours.  If it needs to last longer than 8 hours it needs to be cooled.

Special containers have been developed that slowly cool the extended semen over 2-3 hours and keep it cool for 48 hours.  The semen needs to be properly extended based on the concentration of the sperm in the ejaculate so that it can withstand the cooling process and still deliver adequate numbers of live sperm to the mare for insemination

If semen needs to last longer than 72 hours, it can be frozen. Frozen semen has these additional advantages and disadvantages. 

Advantages include:

• Semen can be more easily shipped internationally.
• Semen from valuable stallions can be frozen and stored for many years.
• Semen may remain available even if the stallion gets ill, injured or has passed away.
• Stallions that are competing for long periods can still have semen available.

Additional disadvantages include:

• Freezing semen involves additional technology and skill.
• Charges for freezing semen are relatively high.
• Some stallion’s semen does not freeze well.
• Thawing of semen must be very precise and done according to the freezing technique.
• Frozen thawed semen has decreased longevity and therefore has to be inseminated into the mare much closer to ovulation.
• Closer timing of the insemination results in higher costs due to increased frequency of monitoring the mare’s cycle.
• Extenders from frozen semen often are more reactive to the mare’s uterus.

Mare Considerations
Mare management is the other half of the AI success story and involves much more than with the stallion. This involves a breeding soundness exam; induction of estrus; monitoring of estrus; prediction of ovulation; timing of insemination; appropriate storage, thawing and handling of semen; correct insemination technique; post insemination examinations/treatments; and pregnancy diagnosis/evaluation at 14-16 days post ovulation.

The first step is proper selection of a fertile mare and a complete breeding soundness exam. A breeding soundness exam involves a thorough reproductive history, a rectal examination, an ultrasound examination, a vaginal examination, and collection of a uterine culture and cytology.  

Stallion selection based on fertility is also extremely important.  A mare owner can invest thousands into examinations and monitoring of her mare, have everything timed perfectly, and find out the fertility (number of live foals from shipped or frozen inseminations) of the selected stallion is not good. 

The mare must be brought into an ovulatory estrus and monitored closely to properly time ordering of semen, insemination of semen and ovulation.  The cycles are usually checked via ultrasound every 2d until a large follicle is present and then daily (or several times daily for frozen semen) to monitor for ovulation.

Timing of insemination is one of the most important factors of AI success.  Although it can vary greatly depending on the stallion, usually fresh semen will last about 48 hours, cool shipped semen about 24 hours and frozen semen about 12 hours.  It is best placed in the mare prior to ovulation and optimally within 24 hours for cool shipped and 8 hours for frozen semen.

Examinations done after insemination will monitor for ovulation and intrauterine fluid.  Pregnancy checks should be done early enough (14-16d) so that twins can be detected and problems properly addressed.

Summary
It is important to look at all aspects of AI and know what it is all about prior to deciding to get involved.  Remember that this may not be an inexpensive process and there are no guaranteed results.  However, if you are properly informed, make good decisions on choices of mares and stallions, allow your veterinarian to do what is necessary, and keep good communication between all involved, you are likely to enjoy the success and advantages that AI has to offer.