Researchers who evaluated the effects of multiple freezing on stallion semen found it could be still be viable, although pregnancy rates were drastically reduced.
The German study team wanted to evaluate the influence of multiple freezing on sperm quality and fertility across stallions with good and bad track records for frozen semen.
Dr Jutta Sielhorst, from the University of Veterinary Medicine Hanover, and her colleagues found that previously frozen stallion semen may be thawed, diluted and refrozen, but it resulted in stepwise decreases in sperm motility, and membrane and acrosome integrity after each freeze/thaw cycle. The acrosome is a cap-like structure which forms part of the head of sperm cells.
They found that the integrity of sperm chromatin – a complex of DNA and proteins that ultimately forms chromosomes – was unaffected after two and three freeze/thaw cycles.
Overall, pregnancy rates after insemination of mares with refrozen semen were drastically reduced. they reported online in the Journal of Equine Veterinary Science.
In the first experiment, the semen of 10 Hanoverian sires with poor and good records for frozen semen was collected by artificial vagina, centrifuged, extended and frozen in a routine manner.
Semen from each stallion was then thawed, resuspended, put in 0.5ml straws, and refrozen. These steps were repeated and sperm concentration was adjusted to 20 x 106 sperm./ml after a third freezing cycle.
They found that motility and the integrity of sperm membrances decreased with each cycle, regardless of the frozen-semen record of each stallion.
In the second experiment, Hanoverian warmblood mares were inseminated with spermatozoa of two stallions with either good or poor semen freezability originating from the first, second and third freeze/thaw cycle.
Four out of 10 mares got pregnant in the first cycle (40%), but only one out of 10 in the second cycle (10%). None of the 10 mares got pregnant with the third-cycle sperm.
“In conclusion, as expected sperm viability of stallion spermatozoa significantly decreases as a consequence of multiple freezing,” the researchers reported.
“However, sperm chromatin integrity was not affected.
“Pregnancy rates after insemination of mares with refrozen semen are reduced.”
Sielhorst was joined in the study by Christiane Hagen, Daphne Behrendt, Barbara Schuette, Dominik Burger, Gunilla Martinsson and Harald Sieme.
Effect of multiple freezing of stallion semen on sperm quality and fertility
Jutta Sielhorst, Christiane Hagen, Daphne Behrendt, Barbara Schuette, Dominik Burger, Gunilla Martinsson, and Harald Sieme.
The abstract can be read here.