Abstract
Background:
Reproductive efficiency in bucks is a critical determinant of genetic improvement and livestock development programs, particularly in smallholder farming systems where bucks contribute substantially to household income and food security.

Aim:
This study aimed to characterize the molecular weight profiles of sperm proteins and their association with kinematic motility parameters in frozen–thawed semen from Anglonubian, Ettawa Cross, Boer, and Saanen bucks.

Methods:
Frozen semen samples were collected from 16 bucks representing the 4 breeds. Sperm motility and kinematic parameters, including total motility, progressive motility, velocity parameters (VAP, velocity, VSL), linearity (LIN), straightness (STR), amplitude of lateral head displacement (ALH), and beat cross frequency, were analyzed using computer-assisted semen analysis. Sperm proteins were extracted, quantified, and separated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis to determine their molecular weight profiles. ANOVA and Pearson correlation tests were used in this study.

Results:
All breeds produced frozen-thawed semen with acceptable motility parameters for artificial insemination. Boer bucks exhibited significantly lower motility than Ettawa Cross and Saanen breeds (p < 0.05). Saanen bucks exhibited a significant decrease in sperm protein concentrations. SDS-PAGE analysis revealed 8–10 protein bands per breed, with prominent high-intensity bands at 15, 50, and 70 kDa. Correlation analysis demonstrated significant associations between ALH and total motility, progressive motility, STR, and LIN, whereas total sperm protein concentration was not correlated with any of the kinematic traits.

Conclusion:
Variations in sperm protein molecular weight profiles and kinematic motility were evident among buck breeds, suggesting the presence of potential breed-specific markers. These findings provide a foundation for the identification of molecular determinants of fertility and support the development of selection strategies for superior sires in buck breeding programs.

Key words: Buck semen; Kinematic motility; Molecular weight profile; Sperm protein.