This sperm may have come in like a lamb — but it’s out like a lion. A highly fertile one.
Semen stored in an Australian lab since 1968 has been defrosted and used to impregnate 34 Merino ewes, resulting in a live birth rate as strong as that from “ram lamb” sperm frozen for just 12 months.
“We believe this is the oldest viable stored semen of any species in the world and definitely the oldest sperm used to produce offspring,” says researcher Jessica Rickard, a post-doctoral fellow at the Institute of Agriculture and School of Life and Environmental Sciences at the University of Sydney.
Rickard did the original work to determine if the stored semen was viable for artificial insemination.
This involved thawing the donations of “Sir Freddie” the ram, which is stored in small pellets — kept at -196 degrees — in large vats of liquid nitrogen. Rickard and her colleagues then conducted in vitro quality control tests “to determine the motility, velocity, viability and DNA integrity” of the 50-year-old sperm.
“What’s amazing about this result is we found no difference between sperm frozen for 50 years and sperm frozen for a year,” Rickard says.
Out of 56 ewes inseminated, 34 were successfully impregnated. This compares to recently frozen semen from 19 sires used to inseminate 1048 ewes, of which 618 were successfully impregnated. This gives a pregnancy rate of 61 percent for the 50-year-old semen against 59 percent for recently frozen sperm, a “statistically equivalent” rate.
“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,” says Simon de Graaf, an associate professor at the University of Sydney.
A bonus breakthrough of this reproductive biology/genetic research: “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,” de Graaf said. “That style of Merino has since largely fallen from favor as the folds led to difficulties in shearing and increased risk of fly strike.”
So, apparently, avid sweater-wearers can rejoice.
“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.”
