The sperm of four rams stored since 1968 in an Australian laboratory has been thawed and successfully used to inseminate 34 ewes.
Researchers Simon de Graaf and Jessica Rickard of the University of Sydney say it is the oldest sperm inseminated to date to produce offspring.
In addition, their work indicates that the birth rate associated with this sperm is as high as that of sperm frozen for only 12 months.
Our results show the viability of long-term sperm freezing since its fertility has been maintained despite 50 years of storage in liquid nitrogen.
Simon de Graaf, professor at the University of Sydney
“Lambs seem to have the body folds that were common among merinos in the middle of the last century, a feature originally chosen to maximize skin surface and wool yields,” says Simon de Graaf.
Nowadays, however, this sheep species from Spain has largely lost the favor of farmers, because these folds caused problems at the time of mowing.
Scientists say their work is analyzing the genetic advances made by the wool industry over the last 50 years of selective breeding.
Over time, we have tried to make sheep more productive, and these results allow us to conduct comparative analyzes.
Simon de Graaf
Her colleague Jessica Rickard determined whether stored semen was viable for artificial insemination. The first step was to defrost sperm, which was stored as small pellets in large tanks of liquid nitrogen maintained at -196 degrees.
His team then conducted in vitro sperm quality tests to determine the sperm’s ability to move, their speed, viability and DNA integrity.
What is surprising in this result is that we found no difference between frozen sperm for 50 years and frozen sperm for one year.
Of the 56 inseminated ewes, 34 were successfully fertilized. These results are comparable to those of recently frozen seeds. The pregnancy rate is 61% for sperm 50 years against 59% for recently frozen semen, which is statistically equivalent according to scientists.
The following video shows thawed fiftieth spermatozoa:
Sperm samples were donated in the 1960s by the Ledgworth Walker Family Farm. These samples, frozen in 1968 by Dr. Steven Salamon, came from four rams, including Sir Freddie, born in 1963.