Functional integrity of sex-sorted, frozen-thawed boar sperm and its potential for artificial insemination

Despite being developed in its present form 20 years ago, sex-sorting of mammalian sperm is still a work in progress. While relatively successful in cattle and sheep, the unique challenges of incorporating sex-sorted sperm into pig production have not yet been overcome. Generally speaking, boar sperm survive freeze-thawing less well and are required in larger numbers for insemination, while in vitro embryo production of pig embryos is less successful compared to other domestic species Niemann H, Rath D. Progress in reproductive biotechnology in swine. Theriogenology 2001;56:1291-1304]. Due to the large number of sperm required for artificial insemination in pigs, a technique of storing sperm after sorting must be developed while adequate numbers of sperm are allocated into X- or Y-chromosome-bearing enriched pools. Cryopreservation is perhaps the ideal method of storage between sorting and insemination, as it allows unlimited time to build up a sperm bank, whereas liquid-storage requires the use of sperm within days of sorting. The limited number of studies investigating the survivability of sex-sorted, frozen-thawed boar sperm have produced promising in vitro results but poor in vivo outcomes. Before fertility can be improved, the causes of any damage to sperm function during the sex-sorting and freeze-thawing procedures must be more fully understood. Once defined, the source of damage may be minimised and this would lead to increased success rates after in vivo application of sex-sorted, frozen-thawed boar sperm.