Necessity of exact examination of sperm characteristics to assess artificial insemination-subfertile bulls

Conception rates of artificial insemination (AI) have gradually been decreasing in the cattle. In order to overcome this problem, AI centers need supply high-quality frozen semen whose insemination makes cow pregnant efficiently. Semen quality is conventionally assessed under the light microscope with cell biological methods, and only high-quality frozen semen straws are used for AI. However, lower conception rates are occasionally recorded in AI with frozen semen straws from some bulls (AI-subfertile bulls). In this paper, we introduce new methods to assess sperm molecular characteristics to find AI-subfertile bulls.