Conception rates poorer with sexed semen - new Teagasc research

Margaret Donnelly

Margaret Donnelly

New research trial results, published by Teagasc, show that conception rates using sexed semen are poorer than using conventional semen.

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.

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.”

All cows were scanned for pregnancy diagnosis 35 to 40 days after fixed-time AI.

Overall, the conception rate to first service was 61.1pc, 49.0pc and 51.3pc 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- 70pc), indicating that cows responded well to the synchronisation protocol, and inseminations were conducted at a suitable time.

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For sexed semen, however, much greater herd to herd variation in conception rates was noted (range 32pc to 67pc). 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 (66pc), but poor performance with sexed semen (42pc). The cows in these six 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 six herds’?

Inseminating cows too early after heat onset is a likely cause of poor results when using sexed semen, according to Teagasc.

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

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