Louisiana State University (LSU) AgCenter scientists have produced calves from Angus bull semen frozen for more than 40 years. Semen from 25 bulls was collected, processed and stored in liquid nitrogen in the 1960s and in succeeding years into the 2000s, says Louis Godke, professor of reproductive physiology at the LSU AgCenter, who led the research team that conducted the study.
"We believe these normal, viable calves have been produced from some of the longest-stored frozen semen ever reported in the scientific literature," he says. "This helps verify that semen properly processed and stored can last for decades without losing its ability to fertilize and produce viable offspring."
The frozen semen came from USDA and was stored in its National Germplasm Conservatory, a sperm and embryo cryobank in Ft. Collins, CO. More than 200 cows were artificially inseminated, with pregnancy rates greater than 50% for semen from each decade.
“All indications are that the early scientists, who had proposed that properly frozen semen stored in liquid nitrogen at -360°F. would subsequently be viable for many years, appear to have been correct,” says Glen Gentry, LSU reproductive physiologist.
Now that the researchers have shown frozen semen can remain viable over extended times, Gentry says he sees two positive effects for the beef and dairy industries.
“First, these germplasm banks storing frozen semen have a product we know will work for livestock producers,” he says. “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.”
-- LSU AgCenter release