Sperm capacitation in bulls, rams, bucks, and boars: molecular mechanisms and species-specific differences

Capacitation is the process by which sperm undergoes physical, biochemical, and molecular changes to acquire the ability to fertilize an oocyte. The first stage occurs after ejaculation with the removal of cholesterol from the cell membrane, reorganization of the cell membrane, and permission of ion entry into the cell. Intracellular alkalization leads to signaling, resulting in the basic capacitation cascade (sAC-cAMP-PKA-PTP). Consequently, the process of hyperactivation and preparation for the acrosome reaction is completed. Significant interspecies differences are observed in farm animals, and identifying these differences will make important contributions to the development of reproductive technologies. Bull sperm is mostly dependent on heparin-like glycosaminoglycans; however, in ram, seminal plasma proteins are shown to play important roles during capacitation. In goat, the rapid and stress-sensitive capacitation mechanism and the tight zinc-dependent in vivo control of boar sperm are important. Furthermore, early and premature capacitation caused by cryopreservation is called cryocapacitation and directly affects fertilization success. Species-specific capacitation mechanisms have been investigated; however, understanding differences will be beneficial using omics approaches in fertilization prediction and in developing cryopreservation strategies. Moreover, this review compares the molecular mechanisms of sperm capacitation in bulls, rams, bucks, and boars. It highlights species-specific differences and their impact on reproductive technologies.