Bioscientifica Proceedings

Summary. Numerous biological and practical lessons associated with the use of sexed semen have been learnt in the 15 years since it was released onto the commercial market. Over this time, concerns regarding the safety of sex-sorted spermatozoa have been largely allayed through the birth of several million pre-sexed calves, but the major issue that remains is that of reduced fertility. Numerous studies have demonstrated that the process of flow cytometric sorting and subsequent cryopreservation causes reduced in vitro and in vivo fertility of sexed semen, which cannot be wholly compensated for by increasing the number of spermatozoa inseminated. As a result of this diminished fertilising capacity, the use of sex-sorted bull spermatozoa was traditionally only recommended for insemination of heifers, not lactating, superovulated and/or synchronised animals due to the low fertility obtained. However, recent changes to the processing methods used during and after flow-sorting are showing the fertility of 'sexed semen' is improving for the first time in over a decade of commercial activity. With continued research and development of methods to improve the conditions under which spermatozoa are sorted and frozen and concurrent advancements in sorter technology, it is anticipated that the fertility and application of sexed semen will continue to increase.

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