Advances in gender preselection in swine.

Gender preselection using isolated populations of X- and Y-chromosome bearing spermatozoa that have been separated on the basis of DNA content is currently possible in swine and other farm animals, as well as in humans. Semen from most livestock species can now be successfully separated into predominantly X or Y sperm populations before their use for intra-tubal insemination, deep-uterine insemination or for in vitro fertilization (IVF) to produce sexed offspring. Birth of progeny of the desired sex in cattle, sheep and swine under semi-practical conditions has successfully validated the sexing technology. Spermatozoa are separated on the basis of inherent differences in DNA content in the X- and Y-chromosome bearing sperm population using modified flow cytometry/cell sorting technology. Spermatozoa are stained with Hoechst 33342 which binds to the DNA in an amount proportional to the amount of DNA present in the individual spermatozoa. Over 300 animals from various species at several locations have been born using the USDA-Beltsville Sperm Sexing Technology for separating X and Y spermatozoa. Sex ratios are shifted from the normal 50:50 to 85 to 90% of one sex or the other. In swine, offspring have been born as the result of surgical intratubal insemination of separated spermatozoa and also from IVF and embryo transfer. At the present time, standard swine artificial insemination techniques are not optimized for use with the small numbers of flow cytometrically separated X or Y sperm populations. Cattle, swine and rabbit offspring have been reproduced through the second generation with normal morphology and reproductive function. Numerous improvements have been made in the sexing technology since it was first reported in 1989. Increasing the speed of the sexing process to make the application of the technology available to a larger segment of the livestock industry is paramount, even with insemination technology designed for small numbers of spermatozoa.