Doppler assessment of testicular arterial blood flow in stallions: influence of age and 180° spermatic cord torsion.

Doppler ultrasonography is a valuable tool for monitoring testicular hemodynamics, offering improved diagnostic insight and supporting treatment monitoring. However, its use in equine andrology remains limited due to a scarcity of published data and reference values. Therefore, this study aimed to characterize the testicular arterial blood flow patterns in clinically normal stallions and stallions with 180° spermatic cord torsion. Spectral Doppler ultrasonography was performed on both testes of 48 Mangalarga Marchador stallions. Thirty stallions with normal testes were divided into three age groups: young (YN, n = 10), adult (AN, n = 10), and senior (SN, n = 10). Stallions with spermatic cord torsion were classified as either young (YT, n = 10) or adult (AT, n = 8). Doppler indices, including resistance index (RI), pulsatility index (PI), peak systolic velocity (PSV), end-diastolic velocity (EDV), and time-averaged maximum velocity (TAMV), were measured in the supratesticular (Supra) and capsular (Cap) arteries. The effects of torsion, age group, and side (left vs. right) on these parameters were analyzed using linear mixed-effects models. Pearson's correlation coefficients were calculated to assess the associations between variables. The results showed that PSV in the supratesticular artery was higher in senior stallions than in young stallions (P = 0.041). Additionally, senior stallions had a higher PI in the left testis compared to the right testis of both young and adult stallions (P < 0.001). In young stallions, torsed testes had a lower RI in the supratesticular artery compared to normal testes (P < 0.001). In adult stallions, the contralateral testis (the unaffected testis in stallions with torsion) had a lower EDV than normal testes (P < 0.001). In all groups (normal, torsed, and contralateral) of both young and adult stallions, RI, PI, and PSV values decreased, while EDV increased, from the Supra to the Cap region. In conclusion, older stallions exhibited reduced testicular blood perfusion, and both torsed and contralateral testes showed altered blood flow dynamics.