Vaginal plug formation and release in female hibernating Korean greater horseshoe bat, Rhinolophus ferrumequinum korai (Chiroptera: Rhinolophidae) during the annual reproductive cycle

The objective of this study was to investigate morphological characteristics and functional roles of vaginal plug formation and release in female hibernating Korean greater horseshoe bat (Rhinolophus ferrumequinum korai) using optical microscope and scanning electron microscope. Vaginal plug formation begins by part of semen first jetted from cervical region and secretions of vaginal epithelium immediately after mating (at the end of August). These secretions are gradually solidified, accumulated, and moved toward the vaginal introitus while filling the vaginal lumen. This formation process continues through the copulation period and the hibernation period (from end of October to middle of March), maintaining vaginal plug throughout the next pregnancy period (from end of March to end of May). Finally, vaginal plug is discharged to the outside of vagina immediately before giving birth. Normal vaginal structures are taken from the nurturing period (from the beginning of June to the middle of August) and before mating period. Therefore, vaginal plug generated immediately after mating is important as a protective barrier to prevent re-mating with male. In addition, vaginal plug during pregnancy can protect fetus in the uterus from physical stimulation by preventing re-mating with male as a kind of defense mechanism to maintain healthy development of fetus in uterus.