Cooled Semen

The introduction of cooled semen in the horse breeding industry has dramatically changed the process of selecting a suitable stallion to sire your next foal. Finding the right sire can be difficult when you are trying to match the current trends in the industry with your budget and the geographical location of the most desirable stallions. Often the stallion you want to breed to is in Texas, California, New York or as far away as Europe or Australia.

Not long ago it would have required a long expensive haul to get your mare bred to such a stallion, however times have changed. The advent of shipped semen and frozen semen has dramatically and permanently changed the face of the horse breeding industry. Geography will no longer dictate which mares a stallion will breed. All major breeds except Thorobreds have approved the use of cooled semen for breeding mares.


1) Mare owners have a larger selection of stallions to choose from, you can access stallions from geographically distant areas.

2) Your mare can remain under your care or at a nearby breeding station during the breeding process and you can be involved in the breeding decisions if you wish.

3) The use of transported semen allows for control of disease during the breeding process.


  • Cooled semen was developed as an alternative to the use of frozen semen in horses.
  • Frozen semen in horses is a difficult proposition, unlike cattle where it is used extensively.
  • The use of cooled semen involves collection of semen from the stallion a day of so before it will be needed by the mare owner. It is collected from the stallion by the use of an artificial vagina (AV) and a mare in heat or a phantom. It is then taken into a lab area and prepared for shipment.
    • The semen is evaluated for total volume of ejaculate, the number of sperm per ml., and the % motility.
    • The semen is then mixed with a liquid that will optimize sperm longevity and survival. This liquid protectant is called the extender
    • Antibiotics are present in the extender and help to prevent the growth of bacteria in the sample.
  • If left at room temperature (25 degrees centigrade) the extended semen would survive for only a few hours, however if the sample is correctly cooled to 4 degrees centigrade the semen can maintain it’s fertility for 48 hours with most stallions and longer with some stallions (72 hrs).
  • This preservation of semen through slow cooling allows for the shipment of the semen to distant locations.
  • The cooling rate of semen during preparation seems to be the most critical factor in the quality of the sample. Semen needs to be cooled from 37 degrees C to 5 degrees C at a specific rate. Cooling too quickly will significantly damage the semen.
  • Once cooled to 5 degrees the container must be able to hold this temperature for 48 hours.

This process of semen preparation and cooling for shipment has been greatly enhanced by the development of the Equitainer, a commercial cooling and shipping device. There have been other less expensive products on the market, however none can match Equitainer’s cooling rates and maintenance of 5 degree centigrade temperature for the desired 48 hours. The container is lightweight and durable for airline shipment. It is quickly recognized by airport security personnel and is not often held up for security reasons during transit.

Team Work is Required For a Successful Pregnancy


    • Timing is everything in the breeding business and it is especially important when using cooled shipped semen. For the timing to work correctly there must be good communication between the mare owner, the veterinarian and the stallion manager. For everything to go smoothly several things must happen:

      1) The mare must come into heat

      2) The time of ovulation must be accurately predicted

      3) Semen must be ordered by the mare manager and shipped by the stallion manager

      4) Semen must arrive in good condition & in a timely manner.

      5) Mare must be inseminated prior to ovulation

  • The main links in the chain are:

    1) The veterinarian

    2) The stallion manager

    3) The mare owner or manager

    4) The mare

    5) The stallion

    6) The transporter.

    Breakdown in communication or performance of an individual’s responsibility anywhere along the chain can result in failure.


  • The mare will not cooperate; early in the spring mares are unreliable with their heat cycles and may not come in heat or not ovulate on schedule.
  • For one reason or another the semen does not get collected
  • Shipments can get lost
  • Semen does not survive the trip

Each failure is expensive so it is best to be organized and rely on the veterinarian before ordering a shipment of semen.

Frequent internal examinations of the mare by the veterinarian allow for an accurate estimation of when ovulation should occur and is essential in the correct timing of a shipment.

The Normal Sequence of Events When Breeding With Cooled Semen

1) Choose stallion and contact stallion manager well in advance of expected breeding date. Ask the following questions:


How much is the stud fee?

What are the charges for shipped semen?

How many shipments does the initial charge cover?

What are the charges for subsequent shipments?

Collection/shipping Procedure:

Have you shipped semen from this stallion before?

What is his conception rate for shipped semen?

Is a veterinarian involved in the process?

Is an Equitainer used for shipping?

How many doses per shipment?


Will you collect on demand or is collection limited to certain days of the week?

Can we order by a certain time of day and have semen delivered to our mare the next day?

Can you ship by air cargo if needed?

2) Mare Management

  • For the mare to get pregnant we must inseminate her with viable semen just prior to ovulation. This is not as easy as it sounds. Mares are notoriously unreliable, especially early in the spring.
  • The best system is daily teasing with a stallion, but this is not often possible is the back yard.
  • The next best thing to a willing stallion is a willing veterinarian. Examination of the mare by the veterinarian is the first step in determining when to begin breeding..
  • A good rule of thumb is: most mares do not ovulate during the winter months and the first ovulation of the year usually occurs in late March. So, beginning in February is usually not productive.
  • The veterinarian should see the mare in March and determine where she is in her cycle. Once that has been determined, plans can be made.
  • The hormones that are available to control the onset of heat and ovulation can be discussed at this time. Much of the stigma of using hormones to breed horses has been removed.
  • These drugs are very effective and safe. They often make the difference between success and failure.

When Do You Order Semen?

  • At the first sign of heat the mare should be visited by a veterinarian daily and examined.
  • An internal examination of the ovaries will help determine when semen should be ordered.

The mare’s reproductive tract is examined for changes that indicate ovulation is imminent. These changes are best determined with ultrasound. Changes that indicate impending ovulation include:

  • Follicular enlargement
  • Changes in the character of uterine folds

This close monitoring is essential, because accurate prediction of ovulation is the most difficult part of the entire procedure. The semen needs to be delivered into the mare’s uterus just prior to ovulation. If the mare ovulates before insemination she will probably not conceive. If she waits 12 hours longer than expected to ovulate, another shipment will be needed.

  • Once ovulation time has been predicted, the semen is ordered early in the day and the mare is given a shot that will help insure ovulation the following evening.
  • As soon as the semen arrives the following day it is placed in the mare with the use of all plastic equipment. A long narrow straw (pipette) is attached to a syringe; the syringe should not contain a rubber plunger as rubber has been shown to be toxic to some spermatozoa.
  • The semen is then drawn into the syringe barrel.
  • It is placed directly into the uterus through the cervix. It is not warmed first or manipulated in any manner.
  • After insemination is complete the remaining semen is examined for motility. It is best to warm the sample to 37 degrees centigrade prior to examination with a microscope in order to get an accurate reading.
  • With this approach the mare typically ovulates the evening of the insemination or early the following morning.
  • The mare should be checked the following morning to be sure ovulation has occurred. She should be checked prior to the deadline for ordering another shipment just in case she hasn’t ovulated and another shipment is needed.
  • She will need to be bred every 48 hours until she ovulates. It is easy to see that it can get quite expensive if the mare does not ovulate on schedule.
  • Once she has ovulated she should be checked within 12-24 hrs. for uterine discharge that needs treatment and an appointment should be made for a pregnancy check 14-15 days post ovulation.

This procedure can sound difficult and at times impossible to coordinate, but surprisingly most mares become pregnant on one shipment. Patience, communication and expertise are essential for a favorable outcome.


Advantages of Cooled Semen:

  • Access to top stallion without concerns about location
  • No shipping the mare long distances is required


  • Timing is essential
  • Expertise at both geographical locations is required
  • Can become expensive if things don’t go as expected
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Intracytoplasmic Sperm Injection (ICSI)

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