Vaccines for immunological control of fertility in animals.

Fertility control has gained considerable momentum as a management tool to regulate populations of captive and wild animals and to control aggressive behaviour or improve meat quality in livestock. Anti-fertility vaccination (immunocontraception and immunocastration) is a humane alternative to methods that rely on surgical or chemical sterilisation and lethal control. Two types of experimental immunocontraceptive vaccine have been registered for field use in animals. They contain either porcine zona pellucida (PZP) proteins extracted from pig ovaries or synthetic conjugated gonadotrophin releasing hormone (GnRH) peptides. These vaccines require repeated injections and are limited to captive or small populations of free-ranging wild animals. Alternative immunocontraceptive vaccines are actively being developed either to improve efficacy or enable large numbers of wild animals to be targeted. Some employ live genetically modified viruses to deliver immunocontraception and have proved successful under laboratory conditions. The relative merits, risks, social acceptability and regulations controlling the use of existing and novel animal immunocontraceptives are reviewed.