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Results of Sexed Semen Dairy Trial Published

Sexed semen is potentially a revolutionary technology for dairy farming. Large trials conducted on Irish dairy farms in 2013 and 2018 highlighted that conception rates were, on average, poorer with sexed semen compared with conventional semen, but these trials also noted large herd to herd variation. For example, in the 2018 trial a quarter of the herds had better conception rates with sexed semen compared with conventional semen.

Sexed semen is potentially a revolutionary technology for dairy farming

In spring 2019, a controlled trial involving 2,250 cows on 24 farms was carried out to examine the importance of timing of AI when using sexed semen. The results were published at the Teagasc Dairy Open Day, Moorepark ’19 this week.

Teagasc researcher Dr Stephen Butler said: “This 2019 field trial was undertaken to investigate if timing of AI relative to time of expected ovulation affected conception rates achieved with sexed semen. We compared AI using conventional semen or sexed semen at two different times relative to a controlled time of ovulation.”

At the end of a fixed-time AI synchronisation protocol, an injection of GnRH is given to control timing of ovulation, allowing AI at a fixed time 16 hours later, regardless of signs of heat. High fertility cows were identified on each herd, and were synchronised using a fixed-time AI protocol and inseminated by an AI Technician 16 hour  after final GnRH injection with conventional semen (CONTROL-16) or sexed semen (SEXED-16), or with sexed semen at a delayed time (22 h after final GnRH injection; SEXED-22).

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. Conception rates achieved with conventional semen were acceptable and relatively stable in all herds (range 54% - 70%), indicating that cows responded well to the synchronisation protocol, and inseminations were conducted at a suitable time.

For sexed semen, however, much greater herd to herd variation in conception rates was noted (range 32% to 67%). In 8 of the 24 herds, conception rates with sexed semen were equal to conventional semen (60% for both). On the other hand, 6 herds had excellent performance with conventional semen (66%), but poor performance with sexed semen (42%). The cows in these 6 herds responded appropriately to synchronisation and were highly fertile when inseminated with conventional semen, so the question is ‘why did sexed semen not work in these 6 herds’?. We can rule out the sexed semen product as the primary cause, as the remaining 18 herds, on average, had good conception rates with sexed semen (54%), indicating that the sexed semen was also fertile.

If the 6 herds with the poorest conception rates with sexed semen are excluded, the conception rates were 59.9%, 52.6% and 54.7% for CONTROL, SEXED-16 and SEXED-22, respectively. Hence, in these 18 herds, SEXED-16 and SEXED-22 were 88% and 91% as good as CONTROL-16, respectively. Conducting inseminations with sexed semen at 16 and 22 hour after the final GnRH injection resulted in similar conception rates, and supports the concept of delaying the timing of AI to at least 16 hours after heat onset.

Inseminating cows too early after heat onset is a likely cause of poor results when using sexed semen. Farmers need to be aware that sexed semen is a fragile product, and that it’s use needs to be carefully managed.

Dr Butler concluded that the levels of fertility performance obtained in this study, makes sexed semen a viable strategy for generating replacement heifers on commercial farms, but more work is needed to identify the reasons for poor performance with sexed semen in a subset of herds that can achieve excellent performance with conventional semen.

Sexed semen reliably produces a 90% sex bias. With the value of dairy bull calves very low, the need for a reliable sexed semen product has never been greater.

For further information see the event booklet at https://www.teagasc.ie/publications/