Sexing of stallion semen

Separation of X-and Y-chromosome bearing spermatozoa to pre-select the sex of offspring is now possible in most large farm animals including horses. Spermatozoa are separated by flowcytometry based on the amount of DNA that differs between the both sex chromosomes. The purity of the sex selection is very high, however the number of spermatozoa being separated is limited. Therefore AI strategies have to be modified in order to get normal pregnancy rates even with low dose insemination. Recently it was shown that hysteroscopic insemination into the tip of the uterus horn or at the uterine papilla results in acceptable pregnancy rates. This review summarizes the data being provided in literature when both technologies, sperm sexing and low does insemination, are combined, employing freshly collected sorted semen, fresh semen stored for 18h prior to sorting and sorted, frozen/thawed spermatozoa. Several foals have been born so far, but the technology needs further improvement before being advertised for commercial use.