Exploratory associations between quantitative multiparametric testicular ultrasound and semen quality in dogs

Semen quality represents the functional outcome of complex structural, vascular, and physiological processes in the testes. Ultrasonography has been explored as a complementary tool to investigate relationships between testicular morphology and vascularization to semen quality. Techniques such as Elastography and Contrast-enhanced ultrasound (CEUS) provide information on tissue mechanics and micro perfusion, however, documentation of these modalities remains scarce. Multiparametric ultrasound (mpUS) integrating structural and functional testicular assessment remains poorly documented. This study aimed to perform a standardized mpUS assessment of the canine testes to explore relationships between quantitative variables and semen parameters. Twenty-one clinically healthy male dogs underwent a mpUS protocol, including B-mode, Doppler ultrasound, Two-dimensional Shear-wave Elastography (2D-SWE), and CEUS, followed by semen analysis using Computer-assisted Sperm Analysis (CASA) and flow cytometry. Associations between ultrasonographic and seminal variables were explored using Spearman's correlation, and exploratory principal component analysis (PCA). Testicular stiffness showed associations with sperm concentration, motility, kinetics, and sperm membrane integrity (ρ = 0.464-0.597, p < 0.05), whereas Doppler indices were not associated with semen quality. Time-related perfusion parameters were associated with sperm cell populations (ρ = 0.467-0.540, p < 0.05). PCA identified distinct components explaining 63.9% of the total variance (KMO = 0.585; Bartlett's test of sphericity p < 0.001) integrating structural, mechanical, hemodynamic, and seminal variables, highlighting complementary dimensions of testicular physiology. In conclusion, mpUS provides complementary information on testicular structure and function associated with distinct aspects of semen quality, enhancing the physiological interpretation of male reproductive function when applied within a multiparametric framework.