,-.$/"01)$!233456-"$ Sexed Semen Applications in Dairy Cattle

Semen of most mammalian species can be sexed with greater than 90 % accuracy with an instrument called a flow cytometer/cell sorter. Unfortunately, the process is slow relative to the number of sperm in a typical artificial insemination dose. Furthermore, the process damages sperm, although to a lesser degree than current procedures for cryopreservation. Because of these limitations, commercially available sexed semen for artificial insemination has lower sperm numbers per dose (about 2 million sperm) than are used conventionally (usually>10 million sperm/dose). Thus far, there is no evidence that these sexing procedures result in abnormal offspring (Tubman et al., 2004). The main problem with this technology is that pregnancy rates are about 10 percentage points lower than with unsexed semen. Nevertheless, sexed semen is commercially available for many bulls. Most applications will be limited to artificial insemination of heifers, which have higher fertility with fewer sperm than cows, and use of sexed semen with dairy heifers has become widespread. Here, I will summarize potential applications of sexed semen in dairy cattle, assuming that accuracy of sexing semen is greater than 90%, that fertility is about 80 % of fertility of unsexe