Cryotolerance of buck goat spermatozoa: functional and oxidative biomarkers across different age groups

BACKGROUND: Cryopreservation is integral to artificial insemination and germplasm conservation in goats, yet post-thaw sperm survival remains inconsistent due to structural and oxidative damage. Age, a key intrinsic factor, critically modulates sperm functional competence and antioxidative capacity, making it a potential predictor of cryotolerance. Understanding age-associated functional and oxidative biomarkers can refine buck selection strategies to enhance fertility outcomes. OBJECTIVE: To systematically evaluate the influence of age on semen quality, oxidative stress markers, and functional competence of spermatozoa in both fresh and cryopreserved semen of Barbari bucks, with the aim of identifying age-associated functional and oxidative biomarkers predictive of sperm cryotolerance and post-thaw survival. MATERIALS AND METHODS: Eighteen breeding bucks were categorized into three groups: Group I (15 to 25-month young adults), Group II (26 to 40-month mid adults), and Group III (41- to 55-month old adults). Fresh and post-thaw semen was analyzed using CASA, flow cytometry, and biochemical assays for motility, viability, acrosomal and plasma membrane integrity, mitochondrial activity, DNA fragmentation, capacitation status, and antioxidative enzyme activity. RESULTS: Midaged bucks (26–40 months) showed significantly higher acrosomal integrity, antioxidant enzyme activity and genomic stability with better cryotolerance compared with younger and older bucks. Younger bucks exhibited incomplete functional maturation, while older bucks displayed oxidative deterioration, higher DNA fragmentation, and reduced antioxidant defense. CONCLUSION: The optimal age window for semen collection in bucks is mid-aged bucks (26 to 40-month old). Functional and oxidative biomarkers provide better predictors of cryotolerance than conventional semen traits, offering actionable insights for AI programs and germplasm conservation.