Review: Semen sexing – current state of the art with emphasis on bovine species

Abstract

It is approaching three decades since the first public evidence of sex-sorting of semen. The technology has progressed considerably since then with a number of institutions and researchers collaborating to eventually bring this to application. The technical challenges have been quite substantial and in the early years the application was limited to only heifer inseminations. Comparable fertility of sex-sorted semen with conventional semen has been an aspirational benchmark for the industry for many years. Significant investment in research in the primary biology of sex-sorted sperm and associated sorting equipment ensured steady progress over the years and current methods particularly the new SexedULTRA-4M™ seems to have now mostly bridged this fertility gap. The dairy and beef industry have adopted this technology quite rapidly. Other animal industries are progressively testing it for application in their specific niches and environments. The current state of the art in the fundamentals of sex-sorting, the biology of the process as well as new developments in machinery are described in this review.

Effect of delaying the time of insemination with sex‐sorted semen on pregnancy rate in Holstein heifers

“…The plausible explanation for this approach, which was also observed in the previous studies (Bombardelli et al, 2016;Vazquez et al, 2003), was sorting process damage to sex-sorted sperm (Bombardelli et al, 2016;Vishwanath & Moreno, 2018;Winters et al, 2018 TA B L E 3 Effect of sex-sorted semen from different sires on pregnancy rates in Holstein heifers life span of the sperm than non-sorted sperm, acrosomal membrane alterations and early capacitation/pre-capacitation like changes (Schenk, Cran, Everett, & Seidel, 2009). The sorting procedure changed the physiology of sex-sorted sperm, and sex-sorted sperm need less time for capacitation and to be ready for fertilization in the reproductive tract compared to non-sorted sperm (Vishwanath & Moreno, 2018;Winters et al, 2018). Therefore, delaying insemination with sex-sorted semen at closer to ovulation time was a critical approach to get better fertility (Hall, Kasimanickam, Glaze, & Roberts-Lew, 2017).…”

Bovine sperm sex‐selection technology in Japan

“…These studies have revealed the fact that AI with sexed semen is associated with lower conception rates in comparison with conventional semen. The field data on the commercial use of sexed semen also showed that the conception rates were lower in the United States, Denmark, Australia, and Japan . Thus, the definite causes of this issue should be sought as rapidly as possible.…”

“…A recent study reported that the conception rate of a branded sexed semen packaged at 4 million sperm per straw, SexedULTRA 4 M™ developed by STgenetics™, reached that of conventional semen packaged at 15 million per straw . The branded sexed semen is made using improved media during sorting . Thus, these findings suggest that in addition to the number of sperm, other factors are involved in the lower fertility rate of sexed semen.…”

“…Other research indicates that sexed sperm was associated with a lower fertility rate in comparison with unsorted sperm when an equal number of sperm were used, and suggested that a 5‐fold increase in sperm numbers is required to achieve a fertility rate comparable to that of control semen . A recent study reported that the conception rate of a branded sexed semen packaged at 4 million sperm per straw, SexedULTRA 4 M™ developed by STgenetics™, reached that of conventional semen packaged at 15 million per straw . The branded sexed semen is made using improved media during sorting .…”

Superovulation protocols for dairy cows bred with SexedULTRA™ sex‐sorted semen

“…Superovulated cows inseminated with sex‐sorted semen produced a significantly smaller proportion of transferable embryos and significantly larger proportions of unfertilized oocytes and/or degenerate embryos than heifers or cows inseminated with unsorted semen (Mikkola & Taponen ; Monteiro et al, ; Peippo et al, ). With 4M SexedULTRA™ sex‐sorted semen, fertility rates between conventional semen and sex‐sorted semen in single‐ovulating heifers approached equivalence (Vishwanath & Moreno, ); however, no data have been published regarding superovulated cattle. Although the economic impact of using sexed semen in an embryo transfer programme was deemed profitable only in heifers (Hayakawa, Hirai, Takimoto, Ideta, & Aoyagi, ; Mikkola & Taponen ), 4M SexedULTRA™ sex‐sorted semen may be appropriate in cows.…”