Recent field trial studies have highlighted that, on average, the conception rates achieved with sexed semen in lactating dairy cows were approximately 84% of those achieved with conventional semen. This means that if conventional semen conception rates were 60.0%, it would be 50.4% when sexed semen was used. The results were similar if cows were bred using AI after observed heat or using fixed-time AI.

A tightly controlled field trial was conducted in 2019 on 24 dairy herds, with similar cows within each herd receiving conventional and sexed semen from the same team of three bulls (2,250 cows enrolled on the study).

The results indicated that one-third of herds had conception rates with sexed semen that were equal to conventional semen, one-third of herds had conception rates that were 84% of conventional semen, and one-third of herds had conception rates that were 67% of conventional semen.

Hence, large herd-to-herd variation existed despite similar conditions being imposed for all herds indicating that the handling of sexed semen straws on the day of AI is likely much more critical than conventional semen straws.

To maximise the chances of successful pregnancy establishment when using sexed semen, follow each step in the guidelines.

A desktop simulation study was undertaken on a 100-cow herd to assess the economic effect of using sexed semen during the first three weeks of the breeding season.

This was done by simulating herds with different levels of fertility (good, average and poor), and then looking at different conception rates with sexed semen relative to conventional semen (100%, 85% and 70%). The dams identified for sexed semen usage were as outlined in the guidelines.

The key takehome messages are:

  • When the sexed semen conception rate was greater than or equal to 85% of conventional semen, sexed semen usage was more profitable than conventional semen usage.
  • Using sexed semen resulted in reduced conception rates and greater dairy semen costs. Using sexed semen also allowed more beef semen to be used, however, and the increased sale value of beef cross calves (€150/head) outweighed the greater sexed semen costs and reduced conception rates.
  • The financial benefits of using sexed semen were greatest on the most fertile dams in the herd (heifers and cows with good fertility).
  • Sexed semen conception rates that were 85% of conventional semen were necessary for sexed semen to increase profitability.

    • Sexed semen must be treated as a fragile product, targeted at the most fertile females and carefully handled on the day of AI, according to the guidelines. If relative conception rates of 85% can be reliably achieved, it will promote greater uptake and usage of sexed semen. This is necessary before a sex-sorting lab can be established in Ireland, which will allow sexed straws to be made available from all high-EBI bulls.

    Guidelines

    Bull team

  • Pick highest EBI bulls available.
  • Use a team of five bulls or more.

    • Suitable dams

    Heifers

  • Target liveweight and BCS of 3.25.
  • Cycling regularly.

    • Cows

  • Lactation one to four.
  • More than 50 days in milk on day of AI.
  • BCS of 3 or more.
  • Cycling regularly.
  • Free of disorders and uterine infections.

    • Timing of AI

  • Fourteen to 20 hours after heat onset (first standing mount). Practise AM-PM rule if possible. If using once-a-day AI, use conventional semen if time of AI is less than 14 hours after heat onset.

    • Fixed-time AI

  • Costly, but mitigates risk.
  • Facilitates targeted usage of sexed semen on mating start date.

    • Straw handling on day of AI

  • Organise sexed straws into one goblet.
  • Thaw a maximum of two sexed semen straws at a time.
  • Thaw straws at 35°C to 37°C for 45 seconds.
  • Load straws into pre-warmed AI guns and keep warm.
  • Complete inseminations within five minutes.