Superior Post-Thaw Sperm Quality and Fertility of Epididymal Compared with Ejaculated Sperm in Subfertile Stallions.

Overview

• This study compares the quality, viability, and fertility of sperm obtained from the epididymis versus ejaculated sperm in subfertile stallions.
• It investigates how differences in seminal plasma composition, especially electrolytes, correlate with sperm function and fertility outcomes.

Background and Rationale

• Seminal plasma typically supports sperm function during natural breeding by providing nutrients and protective factors.
• However, in assisted reproductive technologies like artificial insemination, seminal plasma’s benefits are uncertain, and it may even be harmful.
• Previous reports indicate that secretions from accessory glands can negatively affect sperm viability and decrease conception rates, particularly in stallions with poor semen quality (subfertile stallions).
• The authors hypothesized that sperm collected directly from the epididymis (where sperm mature and are stored before ejaculation) might have better post-thaw quality and fertility than ejaculated sperm due to avoidance of potentially harmful seminal plasma components.
• They also explored whether differences in the electrolyte composition of seminal plasma correlate with fertility status.

Study Objectives

• To compare post-thaw sperm kinetic parameters (movement characteristics) between epididymal and ejaculated sperm from subfertile stallions.
• To assess structural and functional viability markers in sperm from both sources, including:
  • Plasma membrane integrity
  • Acrosomal integrity (important for fertilization capability)
  • Membrane peroxidation (indicator of oxidative damage)
  • DNA fragmentation (genetic damage)
  • Sperm capacitation status (ability to fertilize)
  • Membrane phosphatidylserine translocation and caspase activation (markers of apoptosis)
• To evaluate fertility outcomes post thawing between sperm from epididymis and ejaculate.
• To analyze electrolyte concentrations in seminal plasma and their association with fertility status.

Methods

• Sperm samples were collected from subfertile stallions both as ejaculates and from the cauda epididymis.
• Sperm kinetics were evaluated using computerized semen analysis (CASA) for objective and quantitative data on motility and movement patterns.
• Flow cytometry was used to assess multiple sperm quality parameters in a detailed manner:
  • Plasma membrane integrity
  • Acrosomal integrity
  • Membrane peroxidation
  • DNA fragmentation
  • Capacitation status
  • Phosphatidylserine translocation
  • Caspase activation
• Electrolyte concentrations, especially sodium levels, were measured in seminal plasma from stallions categorized as fertile or subfertile.
• Post-thaw sperm samples were compared for all parameters and fertility outcomes.

Key Findings

• After thawing, epididymal sperm showed superior motility and kinetic parameters compared to ejaculated sperm in subfertile stallions.
• Structural and functional viability markers (membrane integrity, acrosome status, oxidative stress, DNA integrity) were better preserved in epididymal sperm.
• Markers related to apoptosis and capacitation were more favorable in epididymal sperm, indicating healthier, functionally competent cells.
• Fertility rates (successful conception) were higher when using epididymal sperm rather than ejaculated sperm from subfertile stallions.
• Subfertile stallions had higher sodium concentration levels in seminal plasma compared to fertile stallions, suggesting an association between seminal electrolyte composition and subfertility.

Interpretation and Implications

• The findings suggest that the seminal plasma environment in subfertile stallions may contain factors detrimental to sperm function and fertility, potentially related to altered electrolyte composition.
• Sperm collected directly from the epididymis avoid prolonged exposure to unfavorable seminal plasma, resulting in better preservation of sperm quality after cryopreservation.
• This could have important implications for breeding programs and artificial insemination protocols in horses, especially for stallions with subfertile ejaculates.
• Further research is needed to dissect the specific seminal plasma components responsible for reduced sperm function and to optimize preservation methods.
• Targeted modulation of seminal plasma or use of epididymal sperm might improve fertility outcomes in subfertile stallions.

Conclusions

• This study demonstrates that epididymal sperm has superior post-thaw quality and fertility compared to ejaculated sperm in subfertile stallions.
• Elevated seminal plasma sodium levels in subfertile stallions might contribute to decreased sperm function and fertility.
• Understanding seminal plasma composition and its effects on sperm could lead to better assisted reproductive strategies in horses.