The use of sex-sorted semen in horses

Abstract

The application of sex-sorted semen in horses has historically lagged the bovine industry due to differences in the reproductive physiology and grater variability in equine semen quality. Recent advancements, including SuperGen™ sorters and Ultraplus™ semen processing methods developed by STgenetics® (Navasota, Texas), have significantly improved the efficiency of the sex-sorting process and reduced the sperm damage previously reported. To facilitate the broader use sex-sorted semen in the equine industry, it is essential to address challenges such as shipping cooled semen to a central sorting facility, minimizing oxidative stress and DNA fragmentation, and developing effective methods for short-term cooling or long-term cryopreservation of the sex-sorted sperm. In this study, we evaluated the feasibility of shipping cooled (8 °C) equine semen to a central facility for sorting and assessed the quality of sperm post-sorting and preservation. Results from the improved process showed enhancements in sperm motility, morphology, viability and DNA fragmentation following sex-sorting. Although there was a slight, consistent increase in lipid peroxidation of sex-sorted sperm, the quality of sperm over the first 24 h post-sorting was comparable to that of conventional (non-sorted) cool-shipped semen. Fertility rates with fresh semen did not differ between conventional and sex-sorted sperm. When using frozen-thawed sex-sorted sperm for intracytoplasmic sperm injection (ICSI), consistent blastocyst production was achieved, albeit at slightly lower rates than those observed with conventional semen for the same stallions. Stallion-specific variability may account for some of these differences. Overall, sex-sorted semen used for ICSI resulted in a higher number of embryos of the desired sex compared to those obtained using conventional semen.

Keywords: Fertility; ICSI; Sex-sorted semen; Stallion.