PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Role of the oviduct in maintaining sustained fertility in hens

In poultry, sperm transferred by natural mating or AI into the distal end of the vagina immediately begin their ascent to the uterovaginal junction (UVJ) at the anterior end of the vagina. However, due to an intense selection process in the vagina, less than 1% of the sperm transferred actually reach the UVJ. Those sperm that do reach the UVJ enter numerous tubular invaginations of the surface epithelium of the vagina located in the UVJ mucosa, collectively referred to as the sperm-storage tubules (SST). Sperm residing in the SST lumen are capable of surviving up to several weeks while retaining their fertilizing capacity. Resident sperm are released gradually from the SST while the hen is in egg production, ascend to the site of fertilization, and interact with the next ovulated ovum. In this manner, given the absence of an estrus to synchronize ovulation with copulation, poultry are ensured a population of sperm at the site of fertilization around ovulation. Over the past decade, several new and diverse observations have been published addressing the microanatomy of the UVJ and SST, and the cellular and molecular mechanisms orchestrating oviductal sperm selection and storage. These include the role of sperm mobility in selection and transport, SST numbers in different poultry species and lines of high and low fertility, roles of the immune system and possibly neuroendocrine-like cells in the vagina in sperm selection and storage, and the roles of aquaporins and a fluid exchange mechanisms contributing to sperm release from the SST. The objective of this paper is to review and integrate these observations into a comprehensive understanding of the cellular and molecular events influencing the fate of sperm in the oviduct of the hen, particularly with regard to oviductal sperm selection and storage