Sexed-Sorted Semen and Insemination Timing

Reproductive efficiency is an important factor for successful and profitable dairy herds. In the last twenty years, sexed-sorted semen has become a popular tool for producers to increase the rate of genetic progress, manage heifer inventory, and allow for expanded use of beef semen in their herd. All breedings are important regardless of semen type being used, but if the value of the pregnancy and cost of sexed-sorted semen is greater, selecting the ideal time to inseminate an animal is even more crucial. This newsletter is focused on discussing the ideal timing of insemination of sexed semen in dairy herds.

Occasionally, we hear that breedings with sexed semen should be delayed to improve conception rates. Delayed insemination was proposed because the sexing process changes the way sexed semen performs in the female reproductive tract when compared to conventional semen. Delayed insemination has shown to improve chances of fertilization, but does it result in an increased chance of pregnancy? It was suggested that breedings with sexed semen may need to happen closer to the time of ovulation (delayed when compared to conventional semen), which occurs on average 28 hours after the onset of estrus activity. A few early studies with smaller numbers of breedings supported improved conception rates with delayed breedings (>24 hours after onset of estrus). However, newer research using a substantially greater number of breedings has found different results.

When considering timing of insemination with sexed semen, a variety of factors can be considered. This is relevant because studies that aim to address timing of insemination vary in the reproductive management of the animals being bred.

1. Heifer vs Cow

2. Timed AI (Ovsynch) vs Estrus Detection AI

3. Fertility Programs (Double Ovsynch, Presynch Ovsynch)

4. Breed: Holstein vs Jersey

5. First service, second service, or greater

6. Automated activity monitoring vs visual observation

7. Breeding relative to onset, peak, or end of estrus activity

A recent large study focused on timing of insemination with sexed semen in lactating cows using Ovsynch and automated activity monitoring. They demonstrated that cows on Ovsynch being bred between 16 and 23 hours after the last GnRH shot (Fertiline) of synch had similar pregnancy rates. In comparison, cows bred around 16 hours after the onset of estrus activity had a higher conception rate than cows bred 24 hours or later after the onset of estrus.

Another recent study addressed timing of insemination with sexed semen in heifers based on automated activity monitoring. They found breedings 9-32 hours after the onset of estrus in heifers had similar pregnancy rates, but breedings 25-32 hours after the onset of estrus was best. 17-24 hours after onset of estrus was the second best. Heifers bred 32 hours after the onset of estrus had a reduction in pregnancy rate. In addition, there was not a strong relationship between the timing of insemination based on the peak of estrus or end of estrus activity and pregnancy rates.

Recommendations For Sexed Semen

If Using Timed AI (Ovsynch):

• Overall, if breeding cows using Ovsynch with sexed semen, insemination can be 16-24 hours after GnRH.

• One study showed insemination with sexed semen 16 hours after GnRH yielded higher conception rates than 24 hours after GnRH in primiparous cows. Typically, Ovsynch with conventional semen has the highest conception rate 16 hours after GnRH. There may be a preference towards 16 hours after GnRH when using sexed semen.

• Delayed insemination (>24 hours after GnRH) is not recommended for timed AI in cows.

• Heifers can be submitted to a split TAI 5-day CIDR synch program when using sexed semen. This can improve pregnancy rates and reduce age at conception when compared to automated estrus detection and AI on its own.

• Estrus Detection Using Automated Activity Monitoring

• If breedings are based on automated activity monitoring, timing of insemination should be relative to onset of activity (not the peak or end of estrus activity).

• There is little evidence to support delayed breedings (24 hours after onset of activity) in cows

• Cows with low levels of estrus expression (based on automated activity monitoring) are typically less fertile. Consider avoiding sexed semen and using conventional semen for animals demonstrating less intense estrus activity to optimize pregnancy rate.

• Breedings between 9 and 32 hours after the onset of estrus is acceptable in heifers. This means that the timing of insemination may be more forgiving in heifers versus cows. 17-32 hours after the onset of estrus might be ideal. Delaying breeding greater than 32 hours after onset of estrus is not recommended with sexed semen in heifers.

Final Note

A recent analysis demonstrated a gradual improvement in fertility of sex-sorted semen over the last 20 years. Recommendations regarding use of sexed semen may change with advancements in sorting technology as its fertility becomes similar to conventional semen.