151 Associations of Testicular Size and Arterial Blood Flow with Sexual Development and Semen Characteristics in Dorper Rams Raised in a Subtropical Climate

Spectral Doppler (velocimetric) indices are important indicators of blood perfusion and physiological status of internal organs. Doppler ultrasound is used in andrology to assess the blood flow in the testicular arteries, aiding in the diagnosis of scrotal disorders and abnormal spermatogenesis. It was proposed that blood flow indices measured in the testicular artery, namely, blood flow resistance and pulsatility index, were significant predictors of semen quality in clinically healthy dogs. There is a paucity of studies on the associations of testicular morphology and blood flow dynamics with spermatogenesis in growing rams. Forty-five Dorper rams (24 rams aged 8 to 11 months and 21 rams aged 12 to 24 months) were examined using a portable ultrasound scanner connectecd to a linear-array 7.5-MHz transducer. Measurements of the testes were taken with built-in electronic calipers on images containing the largest cross-sectional area of each testicle in 3 planes (coronal, sagittal, and transverse). Colour and spectral Doppler scans were performed immediately after scrotal ultrasonography to detect the testicular arteries and record the following velocimetric indices: peak systolic velocity (PSV, cm/s), end-diastolic velocity (EDV, cm/s), resistive index (RI = [PSV – EDV)/PSV], and pulsatility index [PI = (SPV – EDV)/mean velocity] of the blood vessels. The length (9.7 ± 0.3 v. 9.0 ± 0.2 cm; mean ± SD) of the testes and scrotal circumference (33.3 ± 0.5 v. 31.8 ± 0.4 cm) were greater (P < 0.05) in sexually mature rams than in peri-pubertal rams. There were no differences (P > 0.05) between the 2 age groups of Dorper rams in mean values for blood flow indices measured in testicular arteries. Semen was collected by ejaculation into the artificial vagina from 38% (8/21) of post-pubertal rams and 21% (5/24) of peri-pubertal animals (Chi-squared test; P < 0.05). Semen volume was negatively correlated with PI of the testicular arteries (r = –0.57, P = 0.04). In summary, the attainment of sexual maturity in Dorper rams maintained in a subtropical climate was associated with significant elongation of testes but not with the changes in testicular volume and blood perfusion. Testicular artery PI was a significant predictor of semen volume in peri-pubertal and sexually mature rams. Based on this and several previous studies, B-mode ultrasonography combined with echotextural analyses of the epididymides and accessory sex glands and serum testosterone measurements provide more useful information on the progression of sexual maturation and present semen quality in rams than the ultrasonographic assessment of testicular dimensions and an array of blood flow indices.