Efficient artificial insemination (AI) is essential for future challenges in the pig industry. Core business for AI companies worldwide is diluting semen from high fertile breeding boars, and by that inseminating many sows. Efficient use of AI boars with high genetic merit is important to maximise dissemination of the genetic progress made in the breeding nucleus. An overview of factors affecting the reproductive efficiency of boars is presented. Boar semen is the most important carrier of genetic progress.