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 requred for artificial insemination in pigs, a technique of storing sperm after sortin must be developed while adequate numbers of sperm are allocated in to X- or Y-chromosome-bearing enriched pools. Cryopreservation is perhaps the ideal method of storage between sorting and insemination, as it allows unlimited time build up a sperm b ank, whereas liquid-storage requires the use of sperm within days of sorting. The limited number of studies investagating the survavibality 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 funciton 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. (C) 2008 Elsevier Inc. All rights reserved.