Use of Doppler indices of vascular impedance for diagnosing testicular degeneration in stallions

Abstract

Spectral Doppler ultrasonography is used to evaluate testicular blood flow in males. Further, the correlation between testicular function and values of Doppler indices, Resistive Index (RI), and Pulsatility Index (PI) were reported in men and several animal species (Velasco and Ruiz. Animals 2020;11:1-13). We have previously shown that stallions with oligospermia associated with medically induced testicular degeneration (TD) have higher values of Doppler indices of testicular blood flow than normal stallions (Pozor et al. JEVS 2014;34:38-9). The goal of this retrospective study was to validate Doppler indices of vascular impedance for the identification of stallions with TD. Medical records from five adult stallions with clinical signs of testicular degeneration (small, flaccid, hypoechoic testes; oligospermia or azoospermia, necrospermia; immature germ cells, detached sperm heads) were reviewed. Three of the five subfertile stallions were later castrated, and severe TD was confirmed histologically. Spectral Doppler ultrasound examination of the marginal aspect of the testicular artery was performed by the same operator, and values of RI and PI were determined for each testis. Doppler indices in the five subfertile stallions were compared with those of five normal fertile stallions, evaluated four times in different seasons, using Kruskal-Wallis One-Way ANOVA method. There were no significant differences betweensubfertile and normal stallions for RI (Mean: 0.66 vs. 0.63, SD: 0.08 vs. 0.11, respectively; P>0.5) or PI (Mean: 1.18 vs. 1.22, SD: 0.23 vs. 0.40, respectively; P>0.5). In addition, information from a pony stallion was obtained over four consecutive years. An initial testicular blood flow evaluation was performed on this stallion at 18 yrs. of age, when good fertility and normal semen parameters were confirmed. Over the four years, the pony stallion's testicular volume decreased from 95 cm3 to 41 cm3. The stallion's total sperm numbers fell from an average of 4.6 billion in Year 1 to 0 in Year 4, indicating progressive TD, which was later confirmed histologically. Values of Doppler indices of vascular impedance in the affected stallion were compared to a pony stallion of a similar size and age with normal testicular and seminal parameters. Doppler indices in the affected stallion did not change significantly over the 4 years evaluated (RI: 0.58 – 0.65; PI: 1.02 – 1.12). Further, the Doppler indices in the affected stallion were not different from the normal pony stallion. Based on data collected from this small population of stallions, Doppler indices of testicular blood flow may not be reliable for diagnosing testicular degeneration in stallions. We have no clear explanation for why the results presented here differ from our previous study. Perhaps different etiologies of TD, acute induced vs chronic progressive, contributed to this difference.