Science

Healthy sheep born from frozen semen 50 years ago

Sir Freddie, a ram born in 1959, was one of four stallions whose sperm was collected in 1968 in Australia to inseminate Merino sheep, highly prized for the quality of their wool. For half a century, his semen was stored frozen in liquid nitrogen at -196°C until a team of scientists at the University of Sydney decided to find out if the samples would still be viable.

According to what they said on Sunday, the answer is yes and to their surprise, the reproductive success achieved with them has been similar to that obtained with semen collected 12 months ago. Of the 56 Merino sheep inseminated in the framework of this experiment, 34 managed to carry the pregnancy to a successful conclusion, as detailed by the Australian centre when making the results public.

By way of comparison, when sperm preserved for 12 months from 19 males were used, 1,048 sheep were inseminated, of which 618 had litters. In other words, the success rate with recently frozen sperm was 61% compared to 59% in 1968, according to figures provided by the authors of the study, who have not yet published in a scientific journal their progress in assisted reproduction. Jessica Rickard, co-author of the research, says they will do so soon.

Sir Freddie, one of the stallions whose sperm were frozen, in a 1969 photo. WALKER FAMILY
“We knew that the semen freezing process is efficient and allows semen to be stored for a long time, but we weren’t sure what the quality of DNA would be after so many years,” Rickard explains via email.

The extraordinary thing, he adds, is that they found no difference between semen frozen half a century ago and semen collected a year ago.

All the sheep that participated in the study were inseminated the same day. “The process takes about 30 seconds per animal. It is very fast and efficient, so it is possible to inseminate several hundred sheep in one day. First, the silk is placed and then the semen is deposited in the uterus. The sheep walks back to the meadow alone”, describes the researcher.

“The lambs were seven months old at the time of finishing the study [they are now eight] and they were all in good health at birth,” she says.

University of Sydney scientists Simon de Graaf and Jessica Rickard pose with the sheep born by artificial insemination MORGAN HANCOCK
Also, the young born with the genetic material of half a century ago have in their body the wrinkle characteristic of the Merino sheep of that time in Australia, says this scientist of the Institute of Agriculture of Sydney specialized in the research of assisted reproduction techniques in domestic and wild animals to improve their efficiency.

In addition to applying this technology to the livestock and wool industry to be able to compare the genetic progress made over the last 50 years in artificial selection processes [through which the characteristics that will pass to the next generations are chosen], the conservation of semen could help prevent the extinction of endangered species.

“We mainly work with sheep, but we can work with any species, from flies to rhinos to dugongs [an endangered vegetarian marine mammal],” says Rickard.

The authors of the paper also mention medical applications in humans, for example, to store more effectively in sperm banks samples from cancer patients who resort to that system before undergoing chemotherapy in order to have children in the future.

Steve Salamon inseminating a sheep in the 1960s
The samples from which the 34 sheep were born came from four males of varieties popular in Australia at that time, Ledgworth, Merryville and Boonoke. The semen was collected in the 1960s by a scientist named Steven Salamon (1918-2017), one of the pioneers in assisted reproduction techniques.

Born in Transylvania, Salamon went to Germany in 1956, during the Hungarian Revolution, and later to Australia, fleeing the Soviet regime. The sheep he worked with belonged to the Walker, a family of farmers with whom he collaborated for many years to improve methods of collecting and preserving sperm without losing quality. The family now numbers some 8,000 sheep and continues to collaborate with research at the University of Sydney.

Throughout his career, Salamon trained hundreds of veterinarians and sheep and goat producers in assisted reproduction techniques. “We think [1968’s] are the oldest viable samples of any species in the world and definitely the oldest from which offspring were born,” says Rickard, who now wants to find out how much longer they could be used. “We still don’t know.

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