Using Cooled or Frozen Semen in Equine AI Programs

According to the American Association of Equine Practitioners (AAEP), using advanced technologies such as cooled or frozen semen, embryo transfer, and gamete inter fallopian tube transfer (GIFT) has given horse breeders a wide range of choices and freedoms when deciding which stallion to use with a particular mare.  These technologies are not new, but have been slower to be adopted and used in the equine industry due to a lower tolerance of equine semen to the processes of cooling or freezing and thawing than some other species.  However, using a form of artificial insemination certainly opens to door to a lot more options than using the tried and true traditional method of shipping mares all over the country for boarding and exposure to a certain stallion.  It also extends the season for a stallion, which can be interrupted due to other obligations such as shows or races.

Cooled semen is semen that has been collected, had an extender added, and was cooled to a temperature of 4-6 degrees Celsius (39 – 43 degrees F).  This semen can be kept for up to 72 hours and still be viable for use with a mare.  During that 72 hours, the semen is usually shipped using a special container that keeps the temperature constant.  Using cooled semen will result in a higher pregnancy rate than when using frozen semen – IF all the protocols are followed to the letter.  Taking short cuts in the procedure results in a lower success rate and fewer foals.  The AAEP has a list of considerations that need to be addressed before attempting to use the cooled semen process.

The advantages of using the cooled semen process include:

·      The location of the stallion is not really critical.

·      Avoids the cost, stress, and danger of shipment for the mare and foal.

·      Avoids the risk of exposure to contagious diseases at the boarding and breeding facilities.

·      Increases the ability to select a stallion with the desired pedigree and/or performance records.

Disadvantages are:

             ·      Some stallions having acceptable fertility using fresh semen will not maintain that level of fertility when their semen is cooled and shipped.

             ·      More sperm is necessary for good pregnancy rates when compared to using fresh semen for AI.

             ·      Good mare management is crucial for an acceptable pregnancy rate.
       ·      Costs of equipment, supplies, semen, semen transport, and veterinary costs can offset any savings.

Generally, pregnancy rates for a given stallion run 5 to 10 percent lower using cooled, shipped semen rather than fresh semen.  The range of fertility results runs from 0% to 70%.  This wide variation points out the necessity of good management and quality control in the process of using cooled, shipped semen for breeding mares.

The advantages and disadvantages of using frozen semen are similar to those associated with using cooled semen for breeding.  One additional advantage is that once frozen, the sperm can remain viable for a long time, so the timing of breeding can be more flexible.  

Some disadvantages (other than getting access to liquid nitrogen) of using frozen semen include an even lower conception rate (though success rates of around 60% have been reported) and the discrepancy/distinction between using a dose of semen for a breeding session versus using a straw of semen.  Depending on how the semen is processed and frozen, a single straw will likely not contain enough viable semen.  A dose can be up to eight straws, again depending on how they were processed.  Consider the costs associated with the dose required for best results rather than just the cost of a straw of semen.  

Horse owners considering one of these forms of AI should visit with their veterinarian to ensure that the necessary arrangements and details can be satisfied.   There is also more information available through AAEP.