Sexed Semen in Irish Dairy Herds

The principal benefit for dairy farmers of using semen specifically enriched with sperm containing X chromosomes (i.e., sexed semen) is increased numbers of heifer calves born, with approximately 90 per cent of successful pregnancies resulting in a heifer calf.

“The subsequent increased availability of replacement heifers could form a pivotal component of the 50 per cent increase in milk output targeted in Food Harvest 2020,” said Dr Stephen Butler, Teagasc Animal and Grassland Research & Innovation Centre, Moorepark.

Other benefits of sexed semen use include reduced incidence of calving difficulty, as heifer calves are smaller than male calves, allowing farmers to expand herd size by generating greater numbers of heifers while maintaining a biosecure closed herd, and reducing the number of low-value male dairy calves born.

The current technology used to sort sperm containing X or Y chromosomes has a number of limitations. “Only 10 to 15 per cent of the original sperm population entering the flow cytometer are recovered as marketable sexed semen,” said Dr Butler. Furthermore, conception rates in heifers for frozen-thawed sexed semen are assumed to be 53 per cent, compared to figures of 70 per cent for conventional frozen-thawed semen and 66 per cent for fresh sexed semen.

Dr Butler explained: “Data from recently published studies conducted in the USA, Denmark, Switzerland and China indicate that conception rates achieved with frozen-thawed sexed semen in maiden heifers are approximately 75 per cent of those achieved with conventional semen (e.g., conception rate of 70 per cent for conventional semen vs. 52.5 per cent for sexed semen). The reduction in fertility observed when using frozen-thawed sexed semen has, to date, restricted its use to inseminations on maiden heifers.”

As sexed semen is more expensive than conventional semen (€12 to €20 more per straw) and fertility performance will likely be poorer, research is currently being undertaken to model the economic impact of using sexed semen in heifers and lactating cows on Irish dairy farms. Initial observations suggest that use of sexed semen could have important implications for the rate of national herd expansion after the quota regime is removed.

Further results of the study can be found in the article ‘Sexed semen in Irish dairy herds?’ which is featured in the spring 2012 issue of TResearch, Teagasc’s research and innovation magazine available online at: http://www.teagasc.ie/publications/tresearch/index.asp