Ram sperm frozen for 50 years has been awakened to impregnate 34 ewes in Australia.
Researchers from the University of Sydney have thus concluded that artificial insemination using the world’s oldest known viable semen has a successful impregnation rate in sheep equivalent to recently frozen samples.
Associate professor Simon de Graaf and Jessica Rickard used semen that had been stored since 1968 in a laboratory in Sydney to impregnate 34 Merino ewes, with the resulting live birth rate as high as sperm frozen for 12 months.
De Graaf from the Sydney Institute of Agriculture and School of Life and Environmental Sciences at the University of Sydney said it demonstrates the viability of long-term frozen semen storage.
“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 favour as the folds led to difficulties in shearing and increased risk of fly strike,” he said.
Rickard carried out the original work to determine if the stored semen was viable for artificial insemination. This involved thawing the semen, which is stored as small pellets in large vats of liquid nitrogen at -196 C.
She and her colleagues then undertook in-vitro tests on the sperm quality to determine the motility, velocity, viability and DNA integrity of the 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,” Rickard said.
De Graaf said the reproductive biology and genetic aspects of these as-yet unpublished findings were of most interest to him.
“We can now look at the genetic progress made by the wool industry over the past 50 years of selective breeding. 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.
This compares to recently frozen semen from 19 sires used to inseminate 1,048 ewes, of which 618 were successfully impregnated.
That is a pregnancy rate of 61 percent for the 50-year-old semen against 59 percent for recently frozen sperm, a statistically equivalent rate.