Select Sires

Proper Semen Thawing Procedures
Transcript of Select Sires' Reproductive Moment Program
on DairyLine Radio Which Aired March 3, 2005
With Ray Nebel,
Extension Specialist and Professor of Reproductive Management,
Virginia Tech

This week’s Reproductive Moment is with Ray Nebel. This week we are talking about proper semen-thawing procedures. What are the recommendations for the proper thawing of semen?

Bill, the thawing procedures for frozen and thawed semen have really been the same for the last 20 to 25 years. In warm water thawing, I am talking about 90 to 95 degrees Fahrenheit for a minimum of 40 seconds, allowing the semen to come up to that temperature of 90 to 95 degrees. In the research that has been done in the last 20 to 25 years, we have seen no real differences with different thawing times and temperatures that would improve the post-thaw viability of the semen.

Lately, in the popular press articles, there have appeared recommendations for "in the cow" or "pocket thawing" of semen. Why, or why not, for semen processed by Select Sires?

In fact, "pocket thawing" has made a big splash recently for certain extended semen. That semen is extended in a milk diluter, versus the diluter used at Select Sires which is an egg yolk-citrate base. That might not seem like a big difference, but milk allows for transfer of heat much faster than an egg yolk-citrate buffer. In the industry it is about split. About half of the A.I. organizations use milk, and half use the egg yolk-citrate diluter. With the egg yolk-citrate diluter, it is very important that you do not use any cow pocket thaw because the semen does not warm up fast enough. Therefore, more sperm cells are actually damaged during that procedure.

What actually occurs that dictates the warm water thawing procedure?

It really goes back to how the sperm cells are frozen. Antibiotics are added to the sperm cells when the bull is collected. They are checked for viability, then they go to concentration so that the dilution is made and the semen has started initial cooling. Then, the glycerol is added, which allows the sperm to be frozen. After the equilibration time, which allows the sperm to equilibrate with the glycerol, the semen is put in straws and quickly frozen. When I mean quickly, it goes from refrigerator temperature to minus 196 degrees in about ten minutes. That dictates that we thaw semen very quickly, so the thawing of semen in 90 to 95 degree water for the 40 seconds brings it through the crystallization of ice very quickly. There are two things that really happen.

One, the buffer, or the extender, freezes before the cell itself freezes. And as the water in the buffer freezes, it concentrates the salts around the sperm, and that could be toxic to sperm.

The second thing is that the ice crystals themselves form within the sperm cell. We want those crystals to form uniformly, as well as being very small crystals, so this rapid freezing and thawing allows those things to happen at optimum conditions.

Thank you, Ray. That is Ray Nebel, Extension Specialist and Professor of Reproductive Management at Virginia Tech.

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