Molecular components of sperm and in the media surrounding them influence bull fertility. Given this concept, proteins of the seminal plasma modulate crucial functions and events of reproduction, such as sperm motility and capacitation, cell protection, acrosome reaction, fertilization and embryonic development. Sperm proteins are also important for successful fertilization, egg activation and embryo development. Empirical associations between seminal and sperm proteins and fertility in the bovine indicate that these proteins are potential molecular markers of the male reproductive status.