A recent study – undertaken by Teagasc this spring – revealed how timing of AI, relative to the expected time of ovulation, had an effect on conception rates when sexed semen was used.

This a hugely significant finding for the dairy industry as the use of sexed semen has become a very attractive option for dairy farmers due to the fall in the value of the dairy-bull calf.

This trial was completed on the back of a previous trial conducted in 2018; it found that the timing of AI is critical to achieving a successful conception rate with sexed semen.

The 2018 study also found that 25% of farms achieved a fertility performance with sexed semen that was equal to or greater than that of conventional semen.

The 2019 trial

At the recent Moorepark ’19 event, Teagasc’s Evelyn Drake discussed the procedure and findings of the 2019 trial.

She said: “The previous trial was based on natural heats, but for this one we used a synchronisation protocol.

“The reason we synchronised was that we needed to control the timing of ovulation – because we were doing the inseminations based on a certain timeframe.”

At the end of a fixed-time AI synchronisation protocol, an injection of a gonadotropin-releasing hormone (GnRH) was given to mimic a standing heat or the time of ovulation.

Some cows were then inseminated 16 hours after the start of standing heat and others 22 hours after the start of standing heat.

A total of 2,250 cows from 24 herds were involved in the trial. All the cows were parity one to four and calved greater than 50 days.

Three treatments were examined in each herd:
  • Conventional semen 16 hours after GnRH injection (control-16);
  • Sexed semen 16 hours after GnRH injection (sexed-16);
  • Sexed semen 22 hours after GnRH injection (sexed-22).

“We were focused on the 16 to 22-hour timeframe because we know that sexed semen doesn’t live as long in the cow as conventional semen; so we have a shorter timeframe to work with,” explained Evelyn.

The results

All cows were scanned for pregnancy diagnosis 35 to 40 days after fixed-time AI. Overall, the conception rate to first service was 61.1%, 49.0% and 51.3% for control-16, sexed-16 and sexed-22, respectively.

For sexed semen, however, a much greater herd-to-herd variation in conception rates was noted (range 32% to 67%). In eight of the 24 herds, conception rates with sexed semen were equal to conventional semen (60% for both).

On the other hand, six herds had excellent performance with conventional semen (66%), but poor performance with sexed semen (42%).

The cows in these six herds responded appropriately to synchronisation and were highly fertile when inseminated with conventional semen.

“The conventional conception rates were so high, we know it was nothing to do with the synchronisation protocol and we know that the cows were fertile.

“But it was something to do with the handling of sexed semen in these six herds that it did not like and sexed semen is a fragile product. This was not the norm because it performed very well in 18 herds,” explained Evelyn.

If the six herds with the poorest conception rates with sexed semen are excluded, the conception rates were 59.9%, 52.6% and 54.7% for control-16, sexed-16 and sexed-22, respectively.

Hence, in these 18 herds, sexed-16 and sexed-22 were 87.9% and 91% as good as control-16, respectively, and that “compared to 76% in the trial last year”.

Conclusion

The study found that inseminating with sexed semen at 16 and 22 hours after the final GnRH injection resulted in similar conception rates.

These are fantastic results and supports the concept of delaying the timing of AI to at least 16 hours after heat onset.

Evelyn concluded the talk by saying that “sexed semen does work and we have seen in this trial that it does”.

However, she also emphasised “the importance of having the right cows for the job and how fragile of a product sexed semen is; so it must be managed correctly”.

“You have to target the right cow because it is a fragile product so you must have the optimum conditions,” she concluded.