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MADISON, Wis. – Motivated by the desire to get more heifer calves out of a farm’s best cows, the use of sexed semen in dairy herds has grown dramatically in the last five years. Sexed semen was introduced to the industry in 2006, and according to AgSource, 20% of all Holstein breedings used sexed semen in 2020 compared to 8% in 2015. In Jerseys, that number was much higher last year at up to 45%.  
Dr. Paul Fricke, Ph.D., dairy reproduction specialist and professor of dairy science at the University of Wisconsin-Madison, expects these figures to continue to climb. Fricke shared background and new research on sexed semen during a Professional Dairy Producers of Wisconsin Dairy Signal podcast to help shed light on ways of maximizing the fertility of sexed semen. The studies looked at timing of artificial insemination when using sexed semen in first-lactation cows and non-lactating heifers. 
“Sexed semen is a large investment in a farm’s reproduction program, therefore, we want to use it the best way we know how,” Fricke said. “I think a lot of people are trying to use sexed semen the same way they would use conventional semen. But in randomized controlled trials, sexed semen has about 80%-85% of the fertility of conventional semen.” 
When creating sexed semen, sperm are stained with dye and sorted or killed by a laser. As a result, many sperm are damaged or wasted, making it a less fertile option than conventional semen. Therefore, breeding at the optimal time becomes even more important.  
Recent research disproves a concept in the industry that delaying timing of A.I. when using sexed semen is better for fertility. The idea that inseminating later relative to the onset of activity or estrus will lead to increased fertility with sexed semen was tested by Fricke and his team within a synchronized breeding protocol in which timing of ovulation was precisely controlled. 
“One of the negatives of breeding cows to an estrus is that onset of activity is not an exact predictor of when they are going to ovulate,” Fricke said. “You don’t really put semen into cows at an optimal time when you inseminate to an estrus or increased activity. Fortunately, with conventional semen, timing is not as critical because it lasts quite a while in the reproductive tract.” 
Fricke’s team tested the hypothesis that the induction of ovulation earlier relative to a timed A.I. in a Double-Ovsynch protocol will result in more pregnancies per A.I. The study was done on first-lactation cows on three farms in Nebraska, Ohio and Wisconsin. All farms submitted cows for first timed A.I. using a Double-Ovsynch protocol in which cows were inseminated 8 to 12 hours later than normal at 24 hours after induction of ovulation. The recommended interval from induction of ovulation to time of insemination using conventional semen is 16 hours. 
“We know they’re going to ovulate about 28 hours after the final GnRH treatment of the protocol so that gives us the right timing for the best fertility,” Fricke said. “We modified the Double-Ovsynch protocol. Rather than giving the GnRH treatment in the afternoon, we moved it to the morning. That way, we’re inducing ovulation earlier so the interval from induction of ovulation to time of insemination is 24 hours. This is about the time they’re going to ovulate.” 
However, the modification proved negative for fertility. Cows inseminated 24 hours after the last GnRH treatment had fewer pregnancies per A.I. than cows inseminated at 16 hours, experiencing a decrease of 6 percentage points.  
In a similar study done on pasture-based herds in Ireland, cows were inseminated later rather than moving the time of the GnRH treatment. Cows were bred at 16-hour or 22-hour intervals, and the number of pregnancies per A.I. did not differ between the two groups. Breeding later did not increase fertility. In both scenarios, the conception rate for sexed semen was 80%-85% that of conventional semen.
Research shows the ability to synchronize ovulation and do timed inseminations in heifers helps improve conception rates. A study from the University of Florida looked at different protocols where heifers were inseminated with conventional or sexed semen. Heifers inseminated with conventional semen showed no difference in fertility if bred to estrus or timed A.I. However, breeding with sexed semen to an estrus resulted in significantly lower conception rates as compared to timed A.I.  
“This really piqued our interest,” Fricke said. “It probably reflects the fact you have to be very close to the right timing with sexed semen, likely because the sperm is damaged and has a shorter lifespan in the reproductive tract.”
The recommended protocol in this study involved GnRH treatment, a CIDR device for five days, two treatments of prostaglandin and a timed A.I., yielding a 59% conception rate when using sexed semen.  
“We feel that once-a-day detection of estrus is not frequent enough when using sexed semen,” Fricke said. “Furthermore, the biggest cost to raising heifers is days on feed which is determined by when they get pregnant. If you wait for estrus, you’re delaying days to first A.I.”  
Another study at the University of Florida conducted in 2020 looked at the effect of breeding heifers later when using a five-day CIDR protocol. Half of the heifers in the study were inseminated 12 hours later than normal. For those bred with conventional semen, fertility was fairly standard. But conception rates with sexed semen were not good. 
“Research shows that if you’re using a timed A.I. protocol in first-lactation animals, use the standard timing in that protocol when inseminating with sexed semen,” Fricke said. “In a Double-Ovsynch protocol, you would give the last GnRH treatment in the afternoon and breed the following morning.” 
Fricke and his team are wrapping up research that compares various treatment protocols and breeding strategies when using sexed semen on non-lactating heifers. One study examines the fertility of Holstein heifers inseminated with sexed semen after five-day or six-day CIDR-synch protocols or once-daily detection of estrus after treatment with prostaglandin F2 alpha. In addition, Fricke’s team is doing a feed cost analysis to determine cost per pregnancy based on pregnancy rates yielded by different breeding protocols. Their findings will be published this year.
“At an $18 premium per straw, sexed semen is a big investment,” Fricke said. “Therefore, you want to make sure you maximize fertility.”

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