Sperm Selection in Animal Assisted Reproduction

The ejaculate contains a diverse sperm population, some of which are not suitable for fertilization and may succumb to selection within the female reproductive tract. Since only a fraction of the ejaculate is used in assisted reproduction, a high proportion of abnormal or immature spermatozoa will reduce the chances of a positive outcome. When preparing animal semen for assisted reproduction, spermatozoa with characteristics associated with fertility can be selected based on normal morphology, acrosome integrity, motility and chromatin integrity. Although migration techniques such as swim-up are used when preparing sperm for in vitro fertilization, the sperm numbers that can be obtained are too small to be useful for artificial insemination in the majority of livestock species. Filtration with sephadex or glass wool, or separation by magnetic activated cell sorting, have been attempted in the laboratory but have not been applied in the field. Colloid centrifugation can process whole ejaculates successfully in the field. It increases pregnancy rates following artificial insemination in horses and improves cryosurvival in boar and stallion semen. The focus of this chapter will be on how sperm selection can be performed, especially colloid centrifugation. Results from various studies will be reviewed and the use of colloid centrifugation in different species will be considered.