Frozen Semen

There is a tremendous variation in “freezability” among individual stallions.

The following averages are been recognised:

• 30% of stallions in the general population will be “good freezers”

• 40% will be “satisfactory”

• sperm from the remaining 30% will not survive the freezing process with a level of motility sufficient to be used.

There is no direct relationship between fertility of frozen semen and fertility obtained with natural service of fresh semen. The only way to determine whether sperm from a stallion will survive freezing and thawing is to collect and process a number of ejaculates and evaluate the post-thaw motility. Non-motile sperm will have probably been damaged beyond repair and are incapable of fertilization. Motile sperm have retained their locomotive properties, which indicates better survival during processing. Unfortunately, the retention of motility does not guarantee that sperm will be capable of fertilization. Damage to sperm membranes and the acrosome can occur without adversely affecting motility. In this situation, there are apparently normal sperm that are incapable of fertilization.

After a stallion has been "cleaned-out" to delete the old semen stored in the reproductive tract, we perform one or more test freezes. This allows us to customize a semen freezing protocol. Customized protocols differ in the centrifugation and freezing extenders used and the cooling rates employed by the controlled rate freezer. Regardless of the protocol used, the basic elements of the semen freezing process are the same. Immediately following the collection, a small sample of the semen is analyzed to determine sperm concentration and quality. Sperm motility is analyzed using a computer assisted analyzer (CEROS). It provides objective and accurate measurements of sperm motion characteristics.

The semen is diluted and centrifuged to remove the majority of the seminal plasma, which can be harmful to sperm during the freezing process. Centrifugation also concentrates the semen so that a sufficient number of motile sperm can be included in a single insemination dose.

After the seminal plasma has been removed, the sperm pellet is resuspended in an extender which contains ingredients to protect the sperm during the freezing and thawing processes. The extended semen is then loaded into 0.5 ml plastic straws.
One dose (8 straws) contains 800 million sperms with a post-thaw progressive motility of at least 30%.

Each straw is uniquely marked with the stallion's name, registration number, freezing center (+ its lab number) and the lot number / date.

Once all of the semen is loaded, the straws are placed into a controlled rate cell freezer (Sylab). The semen is cooled from room temperature to the desired -196°C.

After the semen has completed the freezing process, it is immersed and maintained in liquid nitrogen in special cryogenic containers.