Fixative composition and sample storage conditions influence the proportion of morphologically normal bull sperm

Area of Science:

• Veterinary Science
• Reproductive Biology
• Animal Science

Background:

• Sperm morphology is crucial for bull breeding soundness evaluations (BBSE).
• Current fixation and storage methods for bovine sperm are not standardized, leading to inconsistencies.
• Variability in methods can affect the accuracy of morphology assessments.

Purpose of the Study:

• To investigate the impact of fixative composition and storage conditions on bovine sperm morphology.
• To identify optimal fixation and storage protocols for accurate and reliable sperm morphology assessment in bulls.
• To provide recommendations for standardizing BBSE protocols.

Main Methods:

• Semen from Angus bulls (n=11) was fixed using various glutaraldehyde-based and neutral buffered formalin (NBF) formulations.
• Experiments evaluated different pH, osmolality, and chemical compositions of fixatives.
• Sperm morphology was assessed using 1000x oil immersion differential interference contrast microscopy.
• Fixative stability was tested at 4°C, 21°C, and 37°C over 28 days.

Main Results:

• Neutral and isotonic adjusted fixatives resulted in the highest percentage of normal sperm.
• 5% NBF with methanol yielded the greatest proportion of morphologically normal sperm.
• 5% NBF with methanol maintained high normal sperm percentages for up to 28 days at 4°C or 21°C.
• Storage at 37°C led to significant deterioration of sperm morphology across all fixatives.

Conclusions:

• Fixative chemical composition, pH, and osmolality significantly influence bovine sperm morphology.
• 5% NBF with methanol is a superior fixative for preserving sperm morphology.
• Storing samples at or below 21°C is critical for maintaining morphological integrity.
• Standardizing BBSE protocols with 5% NBF with methanol and controlled storage temperatures will improve consistency and reliability.