Sexed semen is becoming more and more popular in recent years as there has been more availability due to sexing labs operating in Ireland.

AI companies are saying that the majority of their dairy semen is now sexed and, so far this year, most companies are seeing a slight rise on sexed semen sales compared to last year.

Taking a survey from AI companies across the country to get an update on the cost of AI straws for 2024, the variation between companies is small, but the big difference is whether a farmer will be using sexed semen.

Using an example of a 100-cow herd and assuming a 25% replacement rate, there are also 25 maiden heifers for AI.

The farmer will be using all AI throughout the breeding season for this example, and using an AI technician for all first serves and any repeats.

Beginning with the heifers, assuming all heifers are at target weight and regularly cycling, they will be all suited to sexed semen. As these should be the highest genetic merited group for breeding, all sexed semen could be used here.

Given this herd is well managed and has good fertility, heifers will have a conception rate to first serve of 70% from conventional semen and presume that drops to 60% with sexed semen.

Fifteen heifers should be in calf after first service but there is also a 90% sex bias to be considered: 15 x 0.90 = 13.5 heifer calves and 1.5 bull calves.

Obviously, it isn’t possible to get half of a calf, so for the purpose of the example, there will be 13 heifers and two dairy bull calves.

At this point, many farmers will introduce a stock bull for labour purposes, assuming AI was used on repeats and all remaining 10 heifers were artificially inseminated once more.

There are now 13 dairy heifers coming from maiden heifers but there 30 are needed, so 17 dairy heifer calves must come from the main lactating herd of 100 cows. The costings of using both sexed semen, conventional and a combination of both are below.

Similar to maiden heifers, conception rates will also drop in dairy cows. Conception rates of sexed semen from trials in Ireland can be taken at 50%.

To get 17 dairy heifer calves, from the following calculation it will take 38 sexed semen straws assuming a 50% conception rate and a 90% sex bias.

If the farm is just using sexed semen on maiden heifers, and uses all conventional semen on dairy cows, conception rates should be higher and AI straws will be cheaper, but more dairy straws will be needed and there will be more dairy bull calves on the ground.

Again, 17 heifers will be needed to come from the dairy herd. Calculating this, considering a 60% conception rate and a 50:50 chance of a bull or heifer, there will be 57 straws needed.

Overall, to get cows in calf, there will be less straws needed as conception rates should be higher, but there will be more dairy bull calves and not as many dairy beef calves on the ground, reducing the value and market of calves in the spring.

A mixed approach using both sexed semen and conventional semen is a route, which many farmers have been using for the past number of years.

A common scenario would be using dairy AI for the first three weeks with the exception of cows marked out for beef bulls.

Many farms can only get a technician once a day, so having a cow suitable for sexed semen isn’t always realistic.

Cows should be less than lactation four, 50+ days in milk, optimum BCS and free of any postpartum disorders.

Even ticking all of these boxes, the cow must be 14 to 20 hours after heat onset, which might be in the evening, so a conventional straw would be more suitable.

So, to get 17 replacements from the dairy herd, using half and half sexed and conventional straws, how many straws of each are needed?

Based on the above calculations, using all sexed semen to breed dairy heifers is the most expensive method to artificially inseminate the herd but it has the highest calf value for saleable calves, as seen in Table 5.

Factors that haven’t been considered are submission rates of cows, and market demand for beef calves.