It’s hard to believe the Wisconsin dairy industry already has over a decade of experience using sexed semen. AgSource DHI data shows sexed-semen use gained momentum in 2007 and 2008, with 8% to 12% of Holstein inseminations to sexed semen. That percentage declined until 2016, after which sexed semen has steadily gained in use since. In 2020, the percentage of Holstein inseminations using sexed semen increased to 20%.
Conception rates for sexed semen are generally accepted to be 75% to 90% of conventional semen. This reduction in fertility is possibly caused by sperm cell damage that occurs during the sorting process, or because of lower sperm counts per unit of semen. New sex-sorting technologies have resulted in less sperm cell damage during sorting and a narrowing in the fertility gap, but differences still exist.
Another possibility is the optimal AI timing for sexed semen is different than that for conventional semen. The hypothesis is sex-sorted semen is more developmentally advanced at the time of freezing due to the added time required for the sorting process. If this is true, inseminating later relative to the onset of estrus should result in greater conception rates. In the field, this theory is still being tested.
AI timing studies
The adoption of activity monitors provides new opportunities to more accurately determine the onset of estrus activity in commercial dairy herds. Two studies using activity monitors in Jersey herds (Nebel 2018 and Bombardelli et al. 2016) found delaying the time of insemination to 16 or more hours after reaching the activity threshold when using sexed semen resulted in greater conception rates. A similar study using activity monitors on Holstein heifers (Gunar et al. 2020) found delaying the time of AI to 20 to 24 hours after onset of estrus resulted in greater conception rates for sexed semen.
What has been missing until recently is a comparison of standard versus delayed timing to AI with sexed semen when using a synchronization program. A recent University of Wisconsin-Madison study (by Lauber) altered the timing of AI to sexed semen following a synchronization program. First-lactation, first-service cows following a Double Ovsynch program were targeted for this study. First-lactation, first-service cows should be the most fertile subgroup in the lactating herd and the best candidates for sexed-semen use.
In this study, the timing of the second GnRH injection was altered. One group received their last GnRH injection 32 hours after the last prostaglandin injection, followed by timed AI 16 hours later. The second group had an extended time from the last GnRH to timed AI. Group 2 received their last GnRH injection 24 hours following the last prostaglandin injection, with timed AI 24 hours later.
Contrary to the improved conception rates achieved by delaying insemination based on activity monitors, delaying timed AI in a Double Ovsynch program instead resulted in poorer conception rates. The standard Double Ovsynch group had a 48% conception rate, compared to 41% for the delayed insemination group. On a related note, a different study using CIDR-Synch in heifers came to a similar conclusion that delaying insemination following synchronization did not affect the conception rate to sexed semen.
Here are the take-home messages:
- For timing of AI for sexed semen based on estrus detection, delaying insemination to 16 plus hours after the onset of activity has been shown to improve conception rates.
- For timing of AI for sexed semen based on synchronization, no benefit has been shown by delaying the time of insemination.
Sterry is the Extension agriculture educator in St. Croix County, Wis. Fricke is a University of Wisconsin-Madison Extension dairy reproductive specialist and dairy science professor. This column is provided by the University of Wisconsin-Extension Dairy Team.