Doppler evaluation of testicular arteries of stallions of different ages

Doppler ultrasound is a relevant method of monitoring testicular hemodynamics and widely used in andrological evaluations in humans. Testicular blood flow in men increases with age, while the pediatric phase is characterized by physiological testicular hypo-vascularization (Dudea et al., Medical Ultrasonography. 2010;12:43-51). Doppler ultrasound is rarely used in stallions which explains the lack of information and benchmarks. Variation in blood flow of adult stallions of different ages has, however, been reported (Pozor and McDonnell, Theriogenology. 2004;61:799-810) and should be further explored. The objective of the present study was to evaluate the blood flow pattern of the testicular artery in normal stallions (anatomically positioned testicle) of different ages. Both testicles of 30 Mangalarga Marchador stallions were evaluated by spectral Doppler and subjected to three different groups: Young (30 months-4 years, n=10), Adults (6-9 years, n=10) and Old (10-22 years, n=10). For the spectral mode, resistance and pulsatility indexes (RI and PI, respectively), systolic peak velocity (SPV), end-diastolic velocity (EDV) and timed average mean maximum velocity (TAMMV) were measured from the supra-testicular (Supra) and capsular (Cap) arteries.Stallions were evaluated during the reproductive season and were restrained without sedation. For statistical analysis, overall effect and pairwise testing with Šidák correction was performed. The effect of the predictor variables presence of torsion, age group and side were assessed using mixed models, Pearson correlations were also applied to assess the association between pairs of variables. Results showed higher SPV Supra in Old than in Young stallions (P<0.041) and, when testis were compared, higher PI Supra in left testicles for Old stallions was observed when compared to right testicles for Young and Adult stallions (P<0.001). These findings suggest lower testicular blood flow in Old stallions possible related to degenerative processes resulting in increased blood flow resistance. Higher PI in the left testicles may be related to early development of left testicles and epididymis (Nishikawa, 1959, Tokyo: Shiba Tamuracho Minatoku) and a lesser descent into the scrotum (Bergin et al., Biol. Reprod. 1970;3:82-92). The difference in perfusion between testes may induce more pronounced degenerative processes in the left testis due to its greater exposure to intra-abdominal temperatures.