Use of sexed semen in cattle production

Abstract

Sexing of bull semen (a procedure validated in several other mammal species) is a process for separating X- and Y-carrying spermatozoa. The current process, which has been used by Sexing Technologies for 20 years, relies on cell sorting based on the higher DNA content of X carriers than Y carriers. The observed sexing accuracy is around 91%. Sexed semen (female) currently accounts for 12.5% of first inseminations in France. It is mainly used in dairy breeds, and more commonly in heifers. Its use is the highest in Jersey, Montbéliarde, and Brown Swiss breeds. It is associated with reduced fertility of around 6-8 points compared to conventional semen, but this difference is tending to gradually decrease. No other adverse effects were observed. The resulting progeny show no increase in the rate of de novo mutations in its genome, nor any significant loss of performance on any of the traits analyzed. The main advantage of sexed semen lies in its use in conjunction with two other tools: sexed semen is reserved for the part of the herd that produces replacement heifers while the other cows are crossbred with beef bulls, for a better economic value of the calves not kept for replacement; the choice of the cows mated with sexed semen is greatly improved by genomic evaluation. These three techniques should therefore continue to be developed, especially if the loss of fertility associated to sexed semen is limited.