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Bullish behaviour

TResearch Summer 2023

The sexed semen lab at Teagasc Moorepark is helping to increase the availability of sex-sorted semen from large teams of dairy bulls of a high genetic index. Sexed semen allows greater reliability when predetermining calf sex, which can help bolster the Irish beef and dairy sectors.

The use of sex-sorted semen in dairy production allows predetermination of calf sex with ~90% reliability. At present, the only commercially available method of predetermining offspring sex is by manipulating the relative abundance of viable X- and Y-chromosome bearing sperm.

Recent developments regarding the availability and uptake of sex-sorted semen in Ireland have been remarkable. For example, there was no sex-sorted semen produced in Ireland for the 2021 breeding season, and availability was limited to a combination of a small number of Irish bulls that were moved to a sex-sorting lab in another country (e.g. Cogent in the UK) and imports of non-Irish bulls from other countries (e.g. UK, New Zealand).

In November 2021, Sexing Technologies established a lab at Teagasc Moorepark with the primary objective of stimulating greater availability of sex-sorted semen from large teams of dairy bulls of a high genetic index based on the national breeding index (i.e. Economic Breeding Index, EBI). The sexsorting service was available to all artificial insemination (AI) companies operating in Ireland.

For the 2022 breeding season, the lab at Moorepark produced 85,000 straws for artificial insemination during a fivemonth period. For the 2023 season, Sexing Technologies started sorting at Moorepark in September 2022, and opened a second lab at the National Cattle Breeding Centre in November that same year. The combined output of the two labs for the 2023 breeding season was approximately 230,000 straws. There continues to be additional imports of sex-sorted semen from other countries (mainly UK and New Zealand), meaning that approximately 300,000 straws of sex-sorted semen were available for use in the 2023 breeding season.

The usage of sex-sorted semen must be carefully considered, as overall pregnancy per AI (P/AI) is less for inseminations with sexsorted semen compared with conventional semen. For example, controlled studies using both sexed and conventional semen to inseminate lactating dairy cows in seasonalcalving herds after detected oestrus or timed AI both reported that, on average, P/ AI was ~10% less for sexed semen. Reasons for a deterioration in P/AI following AI with sex-sorted semen include fewer sperm per straw (four million in SS straws vs. 15 million in conventional), damage to sperm during the sorting process and shorter fertile lifespan in the female reproductive tract.

On a positive note, our recent studies reported that a subset of herds achieved P/AI with sex-sorted semen equivalent to P/AI with conventional semen. Still, other herds had poor P/AI with sexed semen. This highlights that it is possible to achieve excellent reproductive performance using sexed semen, but that there is a risk of having a marked deterioration in fertility performance.

As sperm cells within the straw have already been exposed to potentially damaging steps during the sorting process, it is likely that sexsorted semen straws are more susceptible to any errors during the insemination procedure (e.g. thawing temperature, thawing time, cold shock, time from thaw to completion of insemination). When sex-sorted semen was used fresh (i.e. without cryopreservation), field data generated in New Zealand indicated non-return rates that were comparable with conventional semen. Hence, freeze-thawing is potentially a large source of fertility loss, and needs to be implemented with strict adherence to protocols.

The keys to the successful use of sexed semen are consideration of sire and dam choice, timing of AI, and straw handling on the day of AI. It is likely the difference in P/AI between conventional semen and sex-sorted semen will continue to shrink as technologies for creating sex-biased semen improve, fostering greater usage of sexed semen.

Enthusiasm for using sex-sorted semen has arisen for several reasons:

• Large teams of high Economic Breeding Index (EBI) bulls are available sexed
• Acceptable pregnancy rates are being achieved across thousands of herds
• Using high EBI sexed semen on the best EBI dams accelerates herd genetic gain
• Using sex-sorted semen to generate replacement heifers at the start of the breeding season ensures that all replacements are born at the start of the calving season the following year
• It facilitates a marked increase in the use of high Dairy-Beef Index semen to generate all non-replacement beefcross calves, which could account for over 70% of the total calf crop. These beef-cross calves are more saleable compared with male dairy calves.

Come meet Stephen and the reproduction team at the Moorepark Open day on 4 July where the most up to date research will be presented as well as information for farmers on how to select the best cows for sexed semen.


Teagasc, DAFM Research Stimulus Fund, Dairy Research Ireland, and FBD Trust. 


Stephen Butler, Principal Research Officer, Teagasc Moorepark Research Centre, Fermoy, Co. Cork.

Image credit: smereka/shutterstock.com.