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Breeding Programs with Cooled and Frozen - Thawed Stallion Semen

By: Dr. Sylvia Bedford-Guaus

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Starting a breeding program with either cooled or frozen-thawed equine semen requires knowledge and expertise in collecting and evaluating semen from stallions. With mares breeding with cooled or frozen semen also requires intensively planned breeding management. Cooled or transported semen is not frozen semen, and frozen semen is not cooled or transported semen, although they are often confused or discussed indistinctively.

Cooled or transported semen is semen that has been packaged in a special container for cooling to refrigerator temperature of 39 to 43 degrees Fahrenheit (4 to 6 degrees Celsius) during transport for insemination of mares at distant farms. Cooled semen will only last for 24 to 48 hours, depending on the type of container used for shipment. If the semen is of good quality and is handled adequately, fertility rates with cooled semen are similar to those obtained by performing artificial insemination with fresh semen. Any breeding manager with expertise in handling stallion semen can start a cooled or transported semen program, after minimal training at a referral facility or by a veterinarian. Some universities offer short courses for veterinarians and horsemen interested in cooling stallion semen for transport.

Frozen equine semen is that usually packaged in 0.5-, 2.5- or 5-ml (cc) straws and stored in a liquid nitrogen tank at –320 degrees Fahrenheit (-196 degrees Celsius). In theory, frozen semen can last forever (like a diamond). However, freezing semen for storage is a much more complex procedure than just cooling semen for immediate transport. Freezing semen requires specialized equipment and specialized training. Fertility with frozen-thawed semen is very poor even with good quality semen and very intensive breeding management techniques are used. For this reason, stallions are often taken to specialized centers or referral facilities for this process.

Not all breed associations allow the use of transported or frozen-thawed semen in order to register the offspring. When in doubt, you should always check with your breed registry prior to deciding whether to breed your mare with stored semen.


Every stallion owner or manager can start a transported semen program if shipment of semen is required to breed mares at distant farms. However, minimum requirements should include a breeding shed to collect semen and a laboratory equipped for on-farm semen evaluation. Minimal equipment includes a microscope to evaluate semen, some sort of machine designed to count sperm concentration, an incubator to keep all equipment at body temperature of 98.6 degrees F (37 degrees C), and miscellaneous lab materials to handle and evaluate semen, such as pipettes, microscope slides, plastic cups and graduated cylinders. Additionally, some training in the basics of semen handling and packaging is required.

The semen quality of the stallion is also an important consideration. Any stallion entering a transported breeding program should receive a complete breeding soundness evaluation by an experienced veterinarian specializing in reproduction. A cooling test of the semen should be done on-farm prior to performing any shipments.

Advantages of a Transported Semen Program

  • Avoids the stress of shipping a mare and foal for breeding
  • Increases the gene pool for the particular breed
  • Reduces the use of genetically inferior stallions
  • Eliminates the cost of boarding a mare and foal at a breeding farm
  • Increases the book of mares for the stallion in a given breeding season
  • Reduces the risk of transmission of venereal disease or contagious diseases resulting from boarding the mare and foal at a different farm

    Disadvantages of a Transported Semen Program

  • Requires some training in semen collection and handling techniques, more so than with artificial insemination programs with fresh semen
  • Requires an initial investment in semen collection and handling equipment, unless an artificial insemination program is already in place

  • Requires purchasing semen cooling equipment         

  • Carries possibility that poor quality semen may not survive the cooling/shipment process.        

  • Requires mare in estrus or ovariectomized mare to stimulate stallion for semen collection        

  • Requires more intensive mare breeding management

  • Carries risk of fraud, as when the semen is used for breeding a mare different than that stipulated in the stallion service contract

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