Progress of sex control techniques in mammals

Sex control techniques enable the production of offspring of a specific sex in animals. Methods for achieving sex control in mammals generally fall into two categories: (1) spermatozoa processing pre-fertilization and (2) early embryo sexing after fertilization. This paper reviews and compares spermatozoa processing pre-fertilization based on the physical and chemical characteristics of X and Y spermatozoa, including various sperm separation methods. Early embryo sexing techniques after fertilization are classified into invasive and non-invasive methods. These include karyotyping, polymerase chain reaction based on Y chromosome-specific genes, loop-mediated isothermal amplification based on the specific sequence of Y chromosome, fluorescence in situ hybridization based on a Y-chromosome-specific DNA probe, H-Y antigen detection, X-linked enzyme detection, metabolomics based on the spent culture medium of the embryo, and non-invasive genetic reporter labeling of sex chromosomes. The use of ligands to activate the TLR7/8 signaling pathway in the immunological separation is also reviewed as a potential method for sperm separation. Overall, novel molecular and cell biology methods are enabling the development of sex control technologies, which can positively impact animal production.