World's Oldest Stored Semen Still Viable, Successfully Used To Produce 34 Lambs

The world's oldest semen is 50 years old, and it's still viable. In fact, it appears to have lost none of its potency, despite having been stored in a freezer for half a century. The sample, or rather samples, are not human in origin, but come from a group of Merino rams. Astonishingly, the semen has been successfully used to produce offspring, boasting fertility rates as high as recently stored specimens, CNN is reporting.

In a record-breaking feat, scientists in Australia have used the sperm samples to inseminate dozens of Merino sheep. Said sheep later gave birth to healthy, adorable lambs. According to, the team believes that the 50-year-old sperm is the oldest sample to ever produce offspring -- and the oldest viable stored semen of any species.

"The birth of these lambs clearly demonstrates that artificial insemination with frozen semen is a safe and reliable reproductive technology now and into the future," said Simon de Graaf, an associate professor at the University of Sydney's Institute of Agriculture, which conducted the research.

The semen samples have come from four Merino rams, and were donated in the 1960s by the Walkers, a family of sheep farmers with a long tradition in the trade. The Walker family now runs an 8,000-strong sheep ranch in Yass Plains, New South Wales.

One of the four rams, known as Sir Freddie, was born in 1959. He was bought by the family in 1961 for the sum of 345 guineas, notes CNN.

The sperm specimens went to the University of Sydney's animal breeding program, and were put on ice in 1968 -- being frozen in liquid nitrogen at minus 196 degrees Celsius (or minus 320.8 degrees Fahrenheit). Half a century later, the specimens were defrosted by Dr. Jessica Rickard, a post-doctoral research fellow at the Sydney Institute of Agriculture.

After performing a series of sperm quality tests that checked the motility, velocity, viability, and DNA integrity of the 50-year-old samples, Rickard discovered that the specimens had been very well preserved.

"What is amazing about this result is we found no difference between sperm frozen for 50 years and sperm frozen for a year," she said in a statement.

The samples were used to inseminate 56 Merino ewes, out of which 34 were impregnated and later gave birth to lambs.

"The lambs appear to display the body wrinkle that was common in Merinos in the middle of last century, a feature originally selected to maximize skin surface area and wool yields," said de Graaf.

The numbers showed a pregnancy rate of 61 percent, which favorably compared to the 59 percent success rate that the team obtained with recently frozen semen.

As de Graaf pointed out, the success of the endeavor brings good news not only for veterinarians and conservationists working on breeding program for endangered species, but for human reproduction as well. Given that sperm fertility was proven to maintain during long-term storage, this could help couples who decide to freeze samples before undergoing chemotherapy or other treatments that can negatively impact fertility.

At the same time, the results could benefit programs focused on saving threatened species from extinction.

"The work demonstrates that we can preserve the genetics of rare, endangered animals today so their sperm cells can be used for artificial insemination, IVF or even more advanced reproductive technologies into the future," de Graaf told CNN.