Comparative Study of semen parameters and testicular ultrasonography findings in fertile and sub fertile stallions during the breeding season

Testicular function depends on an adequate vascular supply, which supports spermatogenesis and ensures the maintenance of normal semen quality. Disruptions in testicular blood flow can impair sperm production, highlighting the importance of early detection of vascular and structural abnormalities. This study investigated which seminal, ultrasonographic, and hemodynamic variables remain physiologically stable throughout the breeding season and evaluated their usefulness in distinguishing fertile stallions from those with testicular dysfunction. Ten stallions of different ages were examined monthly from March to June. Seminal quality was assessed using Computer-Assisted Sperm Analysis (CASA) and flow cytometry, while testicular structure and perfusion were evaluated through B-mode ultrasonography, Doppler blood-flow analysis and computer-assisted echotexture assessment (Ecotext). The variables examined included total and progressive sperm motility, sperm kinematic and viability parameters, testicular volume, estimated daily sperm output (DSOe), and Doppler indices including RI, PI, PSV, EDV, TAMV, TABF and TABF rate. Healthy stallions displayed remarkable intra-seasonal stability across all functional and ultrasonographic parameters, confirming the consistency typical of the reproductive period. Conversely, subfertile stallions showed clear impairments, characterized by reduced motility, abnormal echotexture patterns, and notably decreased perfusion-related Doppler variables, particularly total arterial blood flow and TABF rate. These findings indicate that motility parameters, vascular perfusion indices and echotexture descriptors represent the most sensitive indicators of testicular dysfunction. When integrated, these complementary methods provide a comprehensive and clinically valuable framework for the assessment of stallion reproductive function during the breeding season.