Louisiana State University AgCenter scientists have produced calves from Angus bull semen that has been frozen for more than 40 years.
Some of the calves were sired by semen collected and frozen from bulls in the late 1960s, said Robert Godke, a professor of reproductive physiology at the LSU AgCenter.
“These calves are from frozen Angus bull semen stored in liquid nitrogen,” Godke said. The semen was thawed, and beef cows were artificially inseminated at the LSU AgCenter’s Central Research Station.
Semen from 25 bulls – some now deceased – was collected, processed and stored in liquid nitrogen in the 1960s and in succeeding years into the 2000s, said Godke, who led the research team that conducted the study.
The frozen semen, which came from the U.S. Department of Agriculture, was stored in the USDA National Germplasm Conservatory – a sperm and embryo cryobank – in Ft. Collins, Colo., Godke said.
“We believe these normal, viable calves have been produced from some of the longest-stored frozen semen ever reported in the scientific literature,” he said. “This helps verify that semen properly processed and stored can last for decades without losing its ability to fertilize and produce viable offspring.”
David Carwell, an LSU graduate student from Arkansas, was in charge of artificially inseminating more than 200 cows. The results show that pregnancy rates were greater than 50 percent for semen from each decade, which indicates the stored samples maintained their viability, Carwell said.
“We are pleased with these results,” said Glen Gentry, a reproductive physiologist at the LSU AgCenter’s Reproductive Biology Center in St. Gabriel. “That is what one would expect with good-quality semen used to inseminate synchronized cows with frozen-thawed semen stored in liquid nitrogen for only a month.
“All indications are that the early scientists, who had proposed that properly frozen semen stored in liquid nitrogen at minus-360 degrees would subsequently be viable for many years, appear to have been correct,” Gentry said. “We’re happy to have had the opportunity to use some of this long-term stored bull semen to verify what was proposed by the theoretical scientists decades ago.”
Now that the researchers have shown frozen semen can remain viable over extended times, Gentry said he sees two positive effects for the beef and dairy industries.
“First, these germplasm banks that are storing frozen semen have a product that we know will work for livestock producers,” he said. “Second, strides have been made in genetics, and some small differences in DNA — single nucleotide polymorphisms or SNPs — have been shown to be positive production modifiers that can and likely will be used to increase animal production performance.”
SNPs can act as biological markers, helping scientists locate genes that are associated with a variety of traits, such as growth, milk production and disease susceptibility.
“Some of the older bulls in our joint USDA study may have had these SNPs, but science during these animals’ lifetimes had not progressed enough to identify and take advantage of the SNPs,” Gentry said. “Now, because we can use semen that was stored years earlier, we could use that genetic material to identify production traits and hopefully make improvements in our more modern cattle.”
For the long-term, Godke said, “The valuable male sperm stored in the semen tanks will produce babies for a long time.”
The first calf produced from frozen and thawed semen in the United States was born in Janesville, Wis., May 29, 1953.
“It was just one of many thousands that have come from frozen semen over the years,” Godke said. “This important finding was discovered by Chris Polge and his colleagues at Cambridge University in England in the early 1950s.”
Polge was then invited to the United States and shared his findings with colleagues in Wisconsin, Godke said. “And this discovery subsequently changed cattle breeding management and production efficiency for the years to come.”
Today, dairymen can produce as much milk with half as many dairy cows as they did four decades ago, said Ken Bondioli, also a reproductive physiologist and member of the LSU AgCenter research team.
“This is a result good nutrition and genetic improvement through the genetic selection of bulls to use in artificial insemination with frozen-thawed semen on their farms,” Bondioli said. “With frozen semen and artificial insemination, the top, genetically proven bulls can be used to inseminate cows all over the world.”
Records verify that insemination of dairy cattle with frozen semen has resulted in a marked increase milk production per cow since the mid 1960s, he added.
“This is an excellent example where agricultural scientists have developed technologies that have improved animal production efficiency for our livestock producers,” Godke said.
“I am very pleased to have had the opportunity to go to Cambridge and work with Polge in my younger days at the LSU AgCenter,” he added. “He was a very creative, hard-working scientist. I think about him and the impact that his research has made on producers when I see these calves produced by semen that has been frozen for more than 40 years.”
Source: LSU AgCenter