Zona pellucida-sperm binding assay for equine oocytes.

Area of Science:

• Reproductive Biology
• Animal Reproduction
• Fertilization Dynamics

Background:

• Spermatozoon binding to the zona pellucida is a critical initial event in fertilization.
• The number of bound spermatozoa can indicate the functional state of both gametes.
• Understanding factors influencing this binding is essential for reproductive success.

Purpose of the Study:

• To investigate the effect of equine oocyte maturation stage on zona pellucida sperm-binding capacity.
• To compare sperm binding to immature versus mature oocytes.

Main Methods:

• Collection of equine cumulus-oocyte complexes (COCs) from abattoir ovaries and in vivo via ultrasound-guided aspiration.
• Insemination of oocytes directly after collection or after 30 hours of in vitro maturation (IVM).
• Quantification of spermatozoa bound to the zona pellucida.

Main Results:

• Immature oocytes inseminated directly bound significantly fewer spermatozoa compared to mature oocytes after IVM.
• Mature oocytes from preovulatory follicles bound more spermatozoa (324 ± 29) than immature oocytes from non-preovulatory follicles (222 ± 26).
• This difference in binding was not observed when oocytes were matured prior to insemination.

Conclusions:

• Immature equine oocytes exhibit reduced sperm-binding capacity compared to oocytes matured in vivo or in vitro.
• Oocyte maturation status is a key determinant of zona pellucida's ability to bind spermatozoa.
• These findings have implications for understanding equine fertility and improving assisted reproductive technologies.