by Lilly Platts
Sex-sorted semen opens up many possibilities for producers, from targeted replacement heifer production to planned terminal matings.
The process of sorting semen creates challenges, which Dr. Jordan Thomas, University of Missouri, discussed during Fall Focus 2025.
Sex-sorted Semen Adds Options
Thomas began by explaining that to understand the potential benefits of sex-sorted semen, producers need to consider the basic financials of the cow-calf cycle. The number one cost cow-calf producers incur is feed, most of which goes into the cow herd. The second highest cost is replacing open cows, either by developing replacements or purchasing females. For producers who breed for their own replacements, setting those females up for success starts at conception. Females that breed earlier in the season and calve earlier not only have more time to recover and re-breed, but their female offspring are older and consequently start their productive cycle in a better place.
Using 60-day breeding and calving seasons as an example, Thomas explained that the yearly cow-calf cycle is undeniably demanding for females. A cow that gets bred early in the 60-day breeding season will calve at the start of the 60-day calving season. Factoring in a 283-day gestation period, that female will have around 82 days between calving and the next breeding season to recover. A female that breeds at the end of that 60-day cycle will also calve at the end of the 60-day calving season, and only have around 22 days to recover. Females go through a postpartum anestrus period (no heat cycle), and the female that only has 22 days to recover is not going to suddenly jump to the beginning of the 60-day breeding season. “These later-conceiving, later-calving cows don’t just magically become earlier-conceiving cows next year,” Thomas said.
The first breeding and calving season is especially demanding for heifers. Thomas shared that common advice has been to only select heifers born toward the beginning of their calving season, which ensures that they will be more mature when they enter the production cycle. Sex-sorted semen can give producers the option to further home in on the production of replacement heifers both by selecting specific genetics, and also selecting a group of cows to calve earlier in the season. While it might be prohibitive to breed the entire cow herd earlier in the season due to weather or other factors, it could be feasible to do so with a smaller group of females selected exclusively for producing replacements.
Maternal crosses are only one side of the coin with sex-sorted semen. Commercial producers can select more heavily for terminal traits, like carcass and growth, or seedstock producers can be more specific in their matings to produce registered bulls.
Common Challenges
Thomas and his team are currently working on a USDA-funded research project focused on improving the success of sex-sorted semen. The process of sorting semen changes the structure of the sperm cell, which can create challenges. The head of each sperm cell has projections sticking out, and signaling molecules, which are eventually cleaved off in order to interact with the reproductive tract. “What happens with sex sorting is sort of
like what normally happens with capacitation, which is this process of sperm cells acquiring the capacity to fertilize an oocyte. This normally happens in the tract, and with sex-sorted sperm cells, often a larger proportion of them have those important molecules cleaved off. This isn’t necessarily bad because they would go through a process like that anyway, but it changes their useful lifespan,” Thomas explained.
With conventional semen, the timeframe during which sperm cells are traveling and still fertile is longer than with sex-sorted semen. This means that breeding has to be closer in time to a female’s actual ovulation window with sex-sorted semen. Fresh semen can improve this, but logistically this is prohibitive for producers.
Another challenge Thomas and his team are interested in is the differences in fertility rates among bulls. In some scenarios, a bull’s fertility will be different between conventional and sex-sorted semen. “Another thing we propose to address with this grant, which we have honestly really struggled with, is addressing that there are bull-to-bull differences in fertility with sex-sorted semen. Just because a bull has high fertility with conventional semen, believe it or not, doesn’t even mean that he will successfully sort and freeze sexed semen that is viable,” Thomas said.
Above: Dr. Jordan Thomas presenting at Fall Focus 2025. Below: Sex-sorted semen can give producers the option to further home in on the production of replacement heifers both by selecting specific genetics, and also selecting a group of cows to calve earlier in the season.
The shorter fertile lifespan of sex-sorted semen requires more accurately timed AI breeding. Tracking when estrus expression happens—riding, restlessness, etc.—is especially important when using sex-sorted semen. Thomas said, “I think we all forget this, but ovulation occurs quite a long time after the onset of behavioral estrus in cattle. It’s closer to 30 hours after the onset of estrus.”
AI synchronization protocols can be effective, but Thomas cautioned that with sex-sorted semen, tracking estrus expression is still important. Estrus detection aids, like patches, are a good tool for making sure a female for heat more frequently can improve the success of sexsorted semen. “Devote time to check those animals at least three times per day,” Thomas shared. “The reason is, our best recommendation with AI and sex-sorted semen following detected estrus is to be closer to the 18–24-hour window after the detection of estrus for the actual AI to occur, rather than the 12-hour time window that might be more acceptable with conventional semen.”
For example, a female in heat in the morning would still be bred at night with sex-sorted semen, but by adding a check in the afternoon, a female that is in heat midday could be bred the next morning instead of that evening.
Timed AI protocols are popular because when done correctly, producers can get high conception rates in less time, and with less labor. Thomas shared that if a producer wants to utilize sex-sorted semen, they should pick a synchronization protocol that is well-validated with sexsorted semen, and one where animals actually express estrus before breeding.
Sex-sorted semen can open up many possibilities for producers who want to be extremely selective in their mating decisions. Sex-sorted semen is more expensive than conventional, and producers should ensure that their system is set up for success. “I would only consider using sex-sorted semen if females have an activated estrus detection aid, and I would also have conventional semen on hand,” Thomas concluded. .
