Buck Semen Cryobiology: Integrating Biochemical, Hormonal and Functional Evidence

Buck semen cryopreservation supports genetic exchange, conservation and artificial insemination, but successful storage cannot be inferred from post-thaw motility alone. Goat spermatozoa encounter interacting osmotic, membrane, metabolic and oxidative stresses during dilution, cooling, freezing and thawing. The biochemical composition of the ejaculate, endocrine and seasonal conditions of collection, and the functional demands imposed by insemination further complicate interpretation. This critical narrative review integrates foundational and contemporary evidence on these interdependent processes, drawing on goat-specific experiments, endocrine observations, molecular profiling and field fertility studies. Particular attention is given to seminal-plasma phospholipase interactions with lipid-containing extenders, the conditional effects of cholesterol loading and non-permeating sugars, the promise and limitations of antioxidant and cell-death-targeted interventions, and the distinction between endocrine correlates and actionable predictors of freezability. Recent lipidomic and metabolomic studies support a richer account of sperm membrane vulnerability but remain constrained by small donor samples, outcome-defined groups, batch effects and insufficient external validation. Controlled extender comparisons suggest that several animal- and plant-derived formulations can preserve laboratory functions, although equivalence in motility, membrane integrity or heterologous fertilisation does not ensure equivalent pregnancy outcomes. Evidence from artificial insemination studies remains considerably thinner than the literature on post-thaw assays. A key synthesis is that cryoresistance is an emergent property of the donor, seminal environment, processing sequence and measurement system rather than a fixed characteristic of a single extender ingredient. Progress requires paired-ejaculate factorial designs, harmonised cryobiological reporting, prospective endocrine and molecular validation, and adequately powered fertility trials that account for insemination route and female-side variation. Biochemical sophistication should therefore be judged by reproductive performance and reproducibility, not by the proliferation of laboratory biomarkers.