Welcome to the Ice Age: Using Frozen Semen and Embryos in
Today’s Horse Breeding Operations
By Debra Ottier
BSc (Agr), MSc
© Iron Horse Equine
The first reported pregnancy with frozen semen was in the 1950’s, yet frozen semen is
only just now being used world wide in the horse industry. Frozen embryos came to light
in the 80’s and now frozen embryos from some of the worlds’ most elite horses are
available for sale on the internet. You now have access to the BEST GENETICS in the
world! But is the industry using all of this technology to its full potential? Just how
many breeders are using the frozen methods of breeding and what are their success rates?
Frozen Semen
In today’s horse industry, there are few breeding operations that utilize frozen semen to
its full capacity. Most mare owners feel it is too expensive and too risky to use frozen
semen due to the lowered success rates compared to transported semen. But is this really
what is happening in the breeding shed?
Frozen semen allows for:
 Stallions to continue a performance career
 Flexibility in the breeding shed
o Allows mare owners to obtain semen anytime, even before their mare
cycles (rather then waiting for the 24 hr notice)
o If collection problems occur, there is a back up in place to not miss a cycle
 Storage of semen after death of stallion
 Banking of genetic information from the stallion
 Shipment of semen worldwide
The Process:
In general, semen is collected from the stallion using an artificial vagina. The semen is
extended with an extender and centrifuged or spun at a speed of 500 x g, which will
concentrate the sperm and remove the
seminal plasma portion of the ejaculate.
The sperm are re-suspended into a
freezing extender containing a
cryoprotectant, glycerol, and egg yolk.
This suspension is then packaged into 0.5
ml straws, shown here, sealed and then
cooled down to 5 ° C. From this
temperature, the straws are then placed in
liquid nitrogen vapour at a temperature of
-120 °C, then plunged into the liquid at a
temperature of -196 °C. The straws are
Figure 1: Frozen semen packaged in 0.5 ml straws then stored at this temperature for future
use. Sperm stored properly at this temperature will survive indefinitely, making this a
secure method of banking the genetic information of the stallion.
Using Frozen Semen:
Frozen semen is becoming more widespread now due to the
acceptance of this technology by most breed associations for
registration purposes. Shipping of the frozen semen can be
done at anytime throughout the year. One does not have to
wait until the mare is ready to order the semen. In fact, you
can have the semen shipped January to December through
the cattle network at a cost of approximately $15 per dose.
Figure 1: Frozen/Thawed
Compared to transported semen, which is approximately $65 Sperm flurescently labelled
within Canada using commercial priority shipping
companies, shipping frozen semen can be cost effective. To breed a mare with frozen
semen, a veterinarian must ultrasound the mare every 6-8 hours until ovulation. Once
ovulation has been determined, the straws are thawed to body temperature as per the
recommendations of the facility which carried out the freeze. This is critical, as the
thawing stage, if not performed correctly, can induce damage to important membranes
required for fertilization. Insemination is slightly different than with fresh semen, and
still uses an insemination rod but with a plunger to push the semen through the straw and
into the uterus of the mare.
Success of Frozen Semen:
Some vets are not skilled in this type of breeding and as a result, a lower success rate in
the industry has been reported. BUT, this technology enables a mare owner to select a
stallion from anywhere in the world. Yes, in the world! So why is everyone not jumping
at this opportunity? As far as cost is concerned, frozen semen will be approximately the
same in costs when comparing to using transported semen. It is based on success. On
average, the success with frozen semen, nationwide, all breeds, is approximately 30-75%.
Why the variation? Handling of frozen semen and timing of insemination are the largest
factors. Anyone interested in using frozen semen should investigate the whole process in
order to achieve higher success. Find a qualified individual to help you with the process,
as a little research will pay off in the long run.
Frozen Embryos
Although embryo transfer has been a common practice in the cattle industry for a number
of years now, it has only recently gained steam in the equine world. Breed registries have
only now begun to allow the use of embryo transfer in the registration of offspring as the
development of blood typing and DNA parentage verification can prevent fraud and
parentage errors. Thousands of embryos have been collected and transferred into
recipient mares since the 1980's with the future looking towards the
importation/exportation of viable frozen embryos, rather than animals. This new age
technology will have a tremendous impact on the equine industry today and in building
the horse of tomorrow.
Embryo Transfer allows for:




Mares to continue performance careers,
Outstanding mares to have more than one offspring per year,
Obtain foals from problem and aged mares, and
Immature two year olds to produce offspring.
Freezing of the embryo allows for:



Time to select the perfect recipient mare
Banking genetic information of the mare for future use
Shipment of embryos worldwide
The Process:
The requirements are first to select a quality recipient mare to carry the foal to term. This
mare needs to have a good reproductive history, be in good health with an adequate plain
of nutrition. Both the donor mare and recipient mare need to be synchronized such that
ovulation occurs approximately at the same time. This is where most problems arise, as
attempts to synchronize both mares precisely can be difficult.
Once the mares are synchronized, the donor mare is
impregnated. The embryo is flushed at day 7 after ovulation and
transferred into the recipient by a surgical or non-surgical
technique. Pregnancy, if established, is confirmed at day 17.
If one wishes to freeze the embryo and wait until a suitable
recipient mare can be found to match the donor mares’ cycle, the
following occurs:
The donor mare is inseminated, the embryo is collected on day 6.5 or day 7.5 after
ovulation (depending upon whether fresh or frozen semen is used). The embryo is then
frozen for later use by suspending the embryo in an appropriate holding and freezing
media and packaging into a straw. The processing of embryos requires a much slower,
step rate of cooling then is seen with sperm, with the first cooling to -6C at 4C/minute,
then 0.3 C/minute to -35 C. This would require a programmable freezing unit, which
can be quite an expensive piece of equipment (over $20,000). Therefore, only
specialized facilities would have this technology.
Pros and Cons of Using Frozen Embryos:
Why is freezing the embryo beneficial? If you wish to bank the genetic information of
the mare, this is the most reliable method to do so, as freezing
eggs is very difficult in the horse due to collection problems.
Also, if you wish to perform an embryo transfer, the number one
reason why ET fails is that the recipient mare is not exactly
timed one day behind the donor mare, resulting in death of the
embryo once transferred. By freezing the embryo, one can wait
until the recipient mare is ready. The drawback? By undergoing
Figure 3: Embryo photo
freeze/thawing, the embryo is only one, if you have a 40%
courtesy of Minitube Canada
loss, you have a dead embryo. When we compare this to
frozen semen, a stallion will provide over 8 billion sperm per ejaculate. If you have a
40% loss of sperm, you will still have over 5 billion sperm that survive the freeze/thaw
process and have the ability to fertilize an egg.
Success of Using Frozen Embryos:
In general, the age and size of the embryo determines the success with reports of 8/13 for
day 6 and 1/10 for older embryos of greater than 250 - 300 m. Research into different
holding media, freezing media have resulted in some increase in success, but overall, the
likelihood of obtaining an embryo to begin with is approximately 50%, then the survival
rate in the freeze/thaw process of the embryo is approximately 30%, then the chances of
the embryo successfully transferring into the recipient is approximately 30%.
This technique can be quite an expensive undertaking. The costs of the drugs for
synchronization of ovulation, with professional fees payable to the veterinarian can
amount to $2,000. Stabling fees for both the donor and the recipient mares, for a period
of approximately 30 days, can add up quite quickly. If one does not have a suitable
recipient mare, some practitioners offer mares for lease or purchase. This ranges from
$1,500 to $7,500 depending upon the source of the recipient. One must not forget the
stud fee which must be taken into account as well. In total, ranges of $4,000 - $12,000
can be expected.
Technology has advanced further such that embryos can be collected and preserved to
enable shipping to a central facility which may have a large herd of recipient mares to
choose from. In this manner, the donor mares can be collected from on farm and a larger
number of recipients are available to synchronize, improving the odds for success.
Although the equine industry is behind in applying the tremendous advances in
reproduction already made in other species, the time will eventually come when a
catalogue of banked genetic material will be available for breeders to choose their next
crop of potential equine athletes.