The most recent results of the sexed semen trial carried out on Irish herds were discussed at the Moorepark Open Day yesterday (Wednesday).

The results show normal unsexed semen with a conception rate of 46% in cows compared to sexed frozen semen with a conception rate of 39% – a difference of 7%. The results for ‘fresh’ sexed semen were worse with a conception rate of 37% for cows and 46% for heifers.

In heifers the results are slightly better overall, with a conception rate for normal ‘unsexed’ semen of 52% and 46% for sexed frozen semen.

Yesterday the Moorepark researchers and Andrew Cromie from ICBF suggested the trial results show that the fertility performance of the frozen sexed semen is much improved compared to previous reports and outperformed expectations.

They also said the performance of the fresh sexed semen was disappointing. The results indicate that the expected 90% gender bias was achieved – that means 90% heifer calves were born.

The game changers

Body condition score data at the time of breeding was also collected on about 4,000 animals that were scanned as part of the trial. The results show that thin cows (less than 2.5 BCS) had a 30% conception rate compared to fatter cows (BCS over 3), which had a conception rate of over 50%. The trend was the same for maiden heifers.

The other significant factor that influenced conception rates was days in milk at insemination. Cows that were longer calved at the time of first in semination with sexed semen will have a greater likelihood of conception. This means for any spring calving farmer considering using sexed semen to have any chance of achieving good results, they would need to be inseminating February-calving cows.

The potential benefits to a dairy farmer and the wider industry of a sexed semen product that delivers 90% heifer calves are transformative. The direct effect of increased numbers of dairy heifer calves born in a herd using sexed semen presents the farmer with a number of options to grow the herd or sell surplus replacements. Many farmers using Jersey crossbreeding won’t have the issue of getting rid of low-value bull calves. On the other hand, there is the potential to use easy-calving short-gestation beef breeds to increase the value of calf output for later-calving cows.

The downsides

Reduced conception rate was and still is a major factor in all herds. For some farmers, getting a bull calf three or four weeks earlier is a better result than the cow slipping from February into March calving.

Only high-fertility herds should use sexed semen and in some cases it is those struggling to get good fertility that will be looking to use sexed semen. As mentioned above, if condition score is under pressure in the herd, then conception rates will be very low.

The other issue with sexed semen is it is more expensive and reduced days in milk, and poorer conception rates will increase the cost of putting the extra heifer calves on the ground.