Review: Semen extenders used in the artificial insemination of swine

This report reviews the latest knowledge on boar semen diluents used in artificial insemination procedures. The requirements of an effective fresh semen diluent are discussed and currently available extenders are compared. Finally, we suggest directions to be taken in future research on this topic. A semen extender should be carefully selected according to its proposed use. For a planned semen storage time lower than 72 h, it is preferable to use a short-term extender. This type of diluent is less expensive and has been associated with a similar reproduction outcome to that of long-term extenders. When semen doses need to be stored for more than 4 days (because of long distances, disease control procedures, etc.), we recommend the use of a long-term extender on a higher sperm concentration to compensate for reduced sperm viability due to ageing. The semen extender must be selected on the grounds of optimal performance (in terms of fertility and litter size), which, in turn, depends on the particular conditions of each pig farm. The choice of extender is crucial given its profound effect on the economic viability of the artificial insemination programme.