SYDNEY, Australia — Ram semen frozen for 50 years has been used to impregnate 34 ewes in Australia — with huge success. Researchers from the University of Sydney say artificial insemination using the world’s oldest-known viable semen has a successful impregnation rate in sheep equivalent to recently frozen samples.
Professors Simon de Graaf and Jessica Rickard with the School of Life and Environmental Sciences at the University of Sydney used semen that had been stored since 1968 in a laboratory in Sydney. They used the semen to impregnate 34 Merino ewes, with the resulting live birth rate as good as for sperm frozen for just 12 months.
“This demonstrates the clear viability of long-term frozen storage of semen,” de Graaf said. “The results show that fertility is maintained despite 50 years of frozen storage in liquid nitrogen. 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. That style of Merino has since largely fallen from favor as the folds led to difficulties in shearing and increased risk of fly strike.”
Rickard did the original work to determine if the stored semen was viable for artificial insemination. That involved thawing the semen, which is stored as small pellets in large vats of liquid nitrogen at -196 degrees. She and her colleagues then undertook in-vitro tests on the sperm quality to determine the motility, velocity, viability and Deoxyribonucleic acid integrity — DNA — of the 50-year-old sperm.
“We believe this is the oldest viable stored semen of any species in the world and definitely the oldest sperm used to produce offspring,” she said.
It was the reproductive biology and genetic aspects of those as-yet unpublished findings that were of most interest to him, de Graaf said.
“We can now look at the genetic progress made by the wool industry over the past 50 years of selective breeding,” he said. “In that time we’ve been trying to make better more productive sheep. This gives us a resource to benchmark and compare.”
Out of 56 ewes inseminated, 34 were successfully impregnated — about 61 percent. That compares to recently frozen semen from 19 sires used to inseminate 1,048 ewes, of which 618 were successfully impregnated — about 60 percent. That’s a statistically equivalent rate.