Drs.  Jörg Aurich, Juliane Kuhl, Alexander Tichy and Christine Aurich, from the University of Veterinary Medicine in Vienna, examined the semen quality of 1,012 frozen and thawed samples from 134 stallions of five different breeds. They calculated the acceptable percentage of ejaculates for AI as well as the doses available.

The researchers found that the most important variable was sperm motility before freezing: The higher this number, the more likely quality post-thaw semen would be found. Thawed semen is considered acceptable for insemination when the sperm's ability to swim in a straight line or in large circles is 35 percent or higher.

The age of the stallion was also an important parameter; there was a marked decrease in acceptable ejaculates in stallions over 9. The researchers suggest that stallions with high breeding values used in competitions should be collected while they are younger and not after they have retired from the competition ring.

While Arabian stallions had above-average acceptable ejaculates, Icelandic and Quarter Horse stallions had below-average ejaculates. Warmblood and Lipizzaner stallions had average numbers. The researchers note that this suggests a genetic basis for semen cryotolerance.

Total sperm count was the most important variable determining the number of doses of semen obtained. Stallions with good semen quality are more likely to yield acceptable semen after thawing, but good sperm motility in raw semen doesn't always correlate to post-thaw semen quality.

The scientists concluded that there are individual stallions that have semen that does not freeze well, though their raw semen is high quality.

Read more at HorseTalk.

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