Dairy cattle semen used for artificial insemination comes in 0.5 mL or 0.25 mL straws, and University of Idaho professor and dairy extension specialist Joe Dalton said that both product sizes offer excellent storage and fertility potential.
During the December Hoard’s Dairyman webinar, Dalton said he often gets asked about the difference in fertility between the two packages. He shared a review of 780,000 inseminations that showed a difference in pregnancy outcome between 0.5 mL and 0.25 mL straws of less than 1%. “Our ability to see a difference on farm will likely not happen so long as semen handling and storage are appropriate,” Dalton noted.
Proper semen handling is key to getting cows pregnant, and a component of that is the thawing process, since semen straws are stored in a frozen state in liquid nitrogen. Dalton said another question he is asked is how many straws can be thawed at one time if multiple cows need to be bred.
“Just because we have 10 cows to breed or 200 cows to breed on a particular day, it doesn’t mean we can break the rules,” he stated. “All the rules still need to be maintained so we are able to generate pregnancies today and in the future from the semen we purchased and are storing in our liquid nitrogen tanks.”
Dalton shared data that showed fertility was similar between cows that were bred first and fourth when one technician was breeding four cows. However, all those cows were being bred within about 10 minutes from when the semen was thawed, and that was very important.
“These technicians were doing an excellent job and being time efficient, getting semen into cows in 10 to 15 minutes, and that’s the range we want to be in,” said Dalton. “When we can control time, temperature, hygiene, and skill, and when we can deposit semen within 10 to 15 minutes, we can thaw more than one straw.”
So, the answer to the question of how many straws can be thawed at one time is, “No more than can be used in 10 to 15 minutes,” Dalton said. “Everyone should know their comfort zone.”
Semen should be thawed in warm water between 95°F to 98°F for 45 seconds. Timing begins when the first straw hits the thaw bath to when the last cow is inseminated, including the time it takes to load the gun and walk to the animals. When cows are not bred within that window, fertility will suffer.
Dalton also noted that straws of semen should not touch when thawing, as research shows this can damage sperm and reduce fertility. If thawing multiple straws, have multiple thaw baths or gently swirl the straws so they stay apart and use a temperature card within a thaw bath to keep them separated, Dalton said.
A special note about sexed semen
When it comes to sexed semen, the rules change a bit.
“Sexed semen is not the same as conventional semen. Even in 2022, it is a different product,” Dalton noted. “We want to make sure we handle it appropriately so we get our return on investment and can generate those pregnant animals and those calves that are highly desired for our business.”
When thawed correctly and then held at the appropriate temperature, research has shown very little decrease in progressive motility for sexed semen within 15 minutes after being thawed. However, when thawed appropriately but then held in a heat shocked system (around 108°F) or a cold shocked system (40°F), sperm motility is greatly affected.
“Sexed semen, packaged in 0.25 mL straws, is very sensitive to semen handling errors. To guard against those handling errors, we shouldn’t be using the 10-to-15-minute rule when thawing. That’s for conventional semen,” Dalton said.
For sexed semen, no more straws should be thawed than what can be used in about five to eight minutes, Dalton advised. Do this to help ensure a return on investment for that more expensive product.
To learn more, watch the December Hoard’s Dairyman webinar, “Back to the basics: Semen handling and tank management.” This webinar was sponsored by Select Sires.