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General remarks

sperma invriezen

Frozen semen is always easy to have on hand as a stallion is in competition or recovering from injury or illness. Also you can use frozen semen internationally. Valuable stallion semen can be stored for an indefinite period. Disadvantages of freezing stallion semen is that the technique used for processing, packaging, freezing, thawing  and insemination of frozen semen does not result with all stallions in  optimal pregnancies. When a stallion competes, one often takes a month or two time to freeze semen from stallions. However, this time for some stallions is way too short.

Fertility of frozen semen will vary because of the technique of freezing, fertility of mares, stallion fertility and management conditions.

Freezing requires skilled staff with experience in sterile techniques, lab procedures, knowledge of sperm and last but not least the stallion.


For centrifugation it is to advise diluting 1 part of semen with 2 parts of extender. Centrifugation can damage the semen. The recovery of sperm is increased when centrifuged in smaller volumes, unfortunately with these smaller volumes the loss of sperm cells will increase. The use of the OptiPrep “cushion” provides an opportunity to centrifuged semen at a 1000G. Centrifuging of semen without  “cushion” is advisable to centrifuge never higher than 600G. Working with a “cushion” indicates that you will receive 95% of the production of cells. It remains important to count the sperm cells before filling the straws even with the use of EquiPure or SSS,  An alternative to freeze semen is collecting the stallion with an open vagina.

Cooling down and extenders

Big differences in temperature are very harmful to spermatozoa. Therefore it is very important to cool the sperm slowly down to 4C. It is important to add the freezing extender drop by drop, because an osmotic shock can occur when a freezing extender is added. Once the freezing extender is added drop wise and swirled  to the sperm, the semen has time to adapt into a new osmotic equilibrium.

Concentration per straw

Progressive motile spermatozoa (PMS) seems to be better in 0,5 ml straws for most stallions. We recommend to assume using 100x10.6 cell per straw. Of course this could be more, but then there is less cryoprotectant in a straw which results in more damage to sperm.


Generally, the faster the sperm is frozen as quickly as it should be thawed. The ideal cooling and warming rate is affected by the composition of the extender, including the concentration of glycerol. Usually 0,5 ml straws were thawed at 37C for 30 seconds, but it is to recommend to use the protocol of the freezing stud farm.