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Whether this be in the treatment of disease, monitoring calf health, increasing production efficiency or improving grass growth, there are now many tools that help drive efficiency and ultimately profitability. One of the biggest changes in genetics has been the adoption of sexed semen with the ability to breed heifers off your best cows and reduce the number of dairy bull calves entering the beef supply chain. This has both helped drive genetic gain whilst also improving social sustainability.
While the adoption of sexed semen has grown across the UK, uptake among grazing herds has been slower. Many farmers remain cautious, concerned about potential losses in conception rates leading to lost days in milk and ultimately revenue loss. This article will examine the financial impact of using sexed semen and show that, even with a slight drop in conception rates, the financial benefit is significant.
The value of a day in milk
Days in milk has long been a key focus in block calving systems, maximising days in milk by driving fertility improvement to increase revenue. Table 1 shows the current value of a lost day in milk, based on the current 5 year rolling average milk price from October 2025.
The value per cow per day is calculated using average yields from the top 53% of animals across 123 herds in the LIC UK database, with an average lactation yield of 5,858 litres. This figure reflects a true value, since the loss of milk would be seen on those served to sexed semen which requires the top 53% of a herd. A day in milk holds significant value for any dairy business, making fertility a critical performance driver – yet this is only half of the story.
Value of selection intensity
The other half of the story lies in the value of selection intensity, which is one of the key advantages of using sexed semen. This benefit comes from enabling farmers to breed from the best animals in their herd. With sexed semen, selecting the top 53% of a herd typically provides enough dairy replacements in a given year. In contrast, using conventional semen would require selecting the top 90% to achieve the same result, assuming all dairy semen is used during the first three weeks of the service period.
Exploring the performance gap between the top 53% and top 90% of the herd is critical. By using the data from the herds mentioned previously, the average difference in production between the top 53% and top 90% is 51.4 kg milk solids. Based on BV’s (Breeding Values) we can assume animals pass on half of this advantage, giving a benefit of 25.7 kg milk solids. Table 2 shows the value of this benefit per heifer born.
The comparison
Block farmers’ reservations about sexed semen often stem from concerns over reduced conception rates. However, several studies have examined the differences. One of the most relevant and current pieces of research was conducted by Teagasc in 2018, showing an average conception rate difference of 10.5%. However, within this there was no pre-selection of cows, even though younger animals generally have a higher chance of conceiving with sexed semen. Other trials have reported smaller differences of 5% shown in a meta-analysis conducted by ICBF in 2022, whilst a German trial conducted by Lenz et.al. (2016) showed no difference in conception rates.
Applying this to a herd setting, if we take a 400-cow herd moving from conventional to sexed semen, we can calculate the days in milk lost due to the use of sexed across the herd. Table 3 compares sexed vs conventional semen, based on expected usage in both scenarios. The calculation assumes service from week 1 to week 12 of a 12-week block, without the use of stock bulls with all dairy semen, used within the first 3 weeks to generate the required replacements.
There is no doubt that using sexed semen comes with an additional cost. However, it also brings extra gains through improved selection intensity. We know the value per heifer is £138, but what does this look like when applied to an entire herd. Table 4 shows this value when applied to the same 400 cow herd as referenced in Table 3.
What if we mated with conventional for six weeks
Many farmers choose to use conventional for longer than stated above, but for accurate comparison, it’s important to compare like for like. If using conventional for six weeks versus sexed semen for three, you would need to select the top 63% of the herd to achieve the same number of heifers. This equates to a 13.9 kg difference in Milk Solids. There is also an added benefit in reducing the length of time heifer calves are born from six weeks to three. This makes heifer management easier and results in better-matured heifers at service the following year, improving liveweight-to-age performance and likely boosting heifer fertility. A study by UNL¹ found heifers born in the first 21 days of a block system had greater weaning, pre-breeding and pre-calving bodyweights, with a greater percentage cycling prior to breeding and a higher number of pregnant heifers. There are also efficiency gains seen in management with routine vaccinations, and tasks like dehorning and weaning becoming easier.
Additional beef calf value
The final factor to consider is the value of additional beef calves born. While this is a secondary consideration, it remains important. Current market prices show average beef calves (Continental/ Native) selling for £335, compared to an average £161 for dairy bull calves – a difference in value of £174 per calf born. With 105 additional beef calves expected under a sexed semen strategy, this equates to £18,270 in additional calf crop revenue, on top of the genetic progress benefits already discussed.
Conclusions
Despite the potential drop in conception rates with sexed semen, the benefits of selection intensity and breeding replacements from a more elite group of cows far outweigh this. When focusing on fertility, it’s easy to prioritise short-term gains through additional days in milk, but we often overlook the long-term cost of compromising herd progress.
The long-term gains from sexed semen not only outweigh lost days in milk but are cumulative, meaning this effect will only multiply over the years of using sexed semen. We’ve already seen this in herds that have narrowed the gap between top and bottom performers, driving additional revenue through improved milk sales.
1)https://livestock.extension.wisc.edu/articles/calves-born-early-in-the-calving-season-have-more-value/
