Ram sperm frozen for 50 years used to impregnate 34 ewes

'Sir Freddie', one of the rams whose sperm was frozen in 1968 (Photo: Walker family/University of Sydney)

Ram sperm frozen for 50 years has been used to impregnate 34 ewes in a trial undertaken by Australian researchers.

Associate Professor Simon de Graaf from University of Sydney said: “The lambs appear to display the body wrinkle that was common in Merinos in the middle of last century, a feature originally selected to maximise skin surface area and wool yields.“

Semen stored since 1968 in a laboratory in Sydney has been defrosted and successfully used to impregnate 34 Merino ewes, with the resulting live birth rate as high sperm frozen for just 12 months. The samples taken from four rams are described as the ‘world’s oldest known viable semen’.

The results from the trial demonstrates the clear viability of long-term frozen storage of livestock semen. 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He said that it was the reproductive biology and genetic aspects of these as-yet unpublished findings that were of most interest to researchers.

“We can now look at the genetic progress made by the wool industry over past 50 years of selective breeding. In that time, we’ve been trying to make better, more productive sheep,” he said. “This gives us a resource to benchmark and compare.”

The researchers believe the semen to be the world’s oldest viable stored semen of any species and the oldest frozen semen to be used to produce offspring.

The semen was stored as small pellets in large vats of liquid nitrogen at -196 degrees, the university said. Researchers then undertook in vitro tests on the sperm quality to determine the motility, velocity, viability and DNA integrity of the 50-year-old sperm.

The original semen samples were donated in the 1960s from sires owned by the Walker family. Those samples, frozen in 1968 by Dr Steven Salamon, came from four rams owned by the Walkers.