Studies on the modification of ram spermatozoa by ejaculation and cryopreservation and the effects of Binder of Sperm Proteins

Abstract

Frozen thawed ram spermatozoa must be deposited directly into the uterus via laparoscopy as they are unable to traverse the cervix in sufficient numbers to achieve acceptable fertility. Seminal plasma has been heralded as a possible solution to this problem, as it appears to enhance sperm cervical transit. However, the mechanism by which seminal plasma, or indeed cryopreservation, alters spermatozoa to subsequently influence cervical transit is unknown. This thesis explores how seminal plasma and cryopreservation affect the structure and function of ram spermatozoa, with the ultimate aim of improving the in vivo performance of cryopreserved ram semen. The findings of this thesis demonstrate that the physiological process of ejaculation and the artificial practice of cryopreservation significantly alter the molecular profile and function of spermatozoa. Seminal plasma exposure confers additional proteins, alters the sperm glycocalyx, protects spermatozoa from immune cells and regulates the timing of capacitation. Cryopreservation also alters the sperm proteome and glycocalyx, possibly increasing susceptibility of this sperm type to dynamic environmental pressures within the female reproductive tract. Further investigation of the degree to which BSPs benefit ram spermatozoa in the female tract is warranted given their significant effects on sperm cryosurvival and physiology demonstrated herein. The importance of this protein family in ram sperm physiology offers a potential avenue for future improvements in the fertility of frozen thawed ram spermatozoa following cervical insemination.