Semen stored since 1968 in a laboratory in Sydney, Australia has been defrosted and successfully used to impregnate 34 Merino ewes, with the resulting live birth rate as high as sperm frozen for just 12 months.
“This demonstrates the clear viability of long-term frozen storage of semen. The results show that fertility is maintained despite 50 years of frozen storage in liquid nitrogen,” said associate professor, Simon de Graaf from the Sydney Institute of Agriculture and School of Life and Environmental Sciences at the University of Sydney.
“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,” de Graaf said.
“We believe this is the oldest viable stored semen of any species in the world and definitely the oldest sperm used to produce offspring,” said colleague Jessica Rickard.
She undertook in vitro tests on the sperm quality to determine the motility, velocity, viability and DNA integrity of the 50-year-old sperm.
“What is amazing about this result is we found no difference between sperm frozen for 50 years and sperm frozen for a year,” Rickard said.
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. This gives a pregnancy rate of 61 per cent for the 50-year-old semen against 59 per cent for recently frozen sperm, a statistically equivalent rate.