Boar spermatozoa in the oviduct

Area of Science:

• Reproductive Biology
• Animal Science
• Sperm Physiology

Background:

• A functional tubal sperm reservoir (SR) is crucial for fertilization in pigs.
• Boar ejaculates contain a sperm-rich fraction (SRF) and a post-SRF fraction with seminal vesicle secretions.
• Spermadhesin PSP-I/PSP-II in secretions attracts leukocytes, aiding phagocytosis of non-reservoir spermatozoa.

Purpose of the Study:

• To investigate the origin and dynamics of spermatozoa within the pig's tubal sperm reservoir.
• To understand the role of the SR in sperm capacitation and fertilization.
• To elucidate the influence of seminal vesicle secretions and oviductal fluid on sperm function.

Main Methods:

• Sequential deposition of marked spermatozoa and SR screening.
• In vitro binding assays with epithelial explants.
• In vitro capacitation studies using SR fluid, seminal vesicle secretions, and oviductal fluid components.

Main Results:

• Spermatozoa in the SR primarily originate from the initial, PSP-poor portion of the SRF.
• The SR replenishes within 2-3 hours, with sperm numbers decreasing towards ovulation.
• Uncapacitated spermatozoa bind to the SR; capacitation increases significantly post-ovulation, influenced by bicarbonate and reversed by SR fluid/hyaluronan.

Conclusions:

• The SR maintains sperm viability before ovulation by limiting capacitation.
• Spermatozoa in varying capacitation stages within the oviduct maximize fertilization success.
• Tubal fluid composition and seminal vesicle secretions modulate sperm capacitation and viability.