Ultrasonography of the penile urethra of healthy Dorper × Santa Ines lambs between 2 and 5 months of age

The objectives of this study were to establish, by ultrasonography, values of the width of the penile urethral lumen of Dorper × Santa Ines lambs, verify the effects of age and Dorper cross degree, and compare two types of linear probes. Forty healthy, uncastrated lambs (18 ½ Dorper and 22 ¾ Dorper) kept confined for fattening were studied. Ultrasonographic examinations were performed at 60 (beginning of confinement period), 120, and 150 days of age (end of confinement period). The penile urethra was examined at four sites: the proximal urethra (perineal region), sigmoid flexure (caudal aspect of the base of the scrotum), distal to the sigmoid flexure (cranial aspect of the base of the scrotum), and distal urethra (half the distance between the glans and the base of the scrotum). Images were acquired in B-mode with transcutaneous cross sections using two types of linear probes: for external use (13 MHz) and for transrectal use in large animals (10 MHz). The urethral lumen width was measured at each anatomical site. Data were analyzed using two-way repeated measures ANOVA. Genetic factors did not influence the results. The image definition was lower for the probe for rectal use. The urethra was identified as a circular or elliptical structure with an anechoic lumen and slightly hyperechoic wall. Urethral width increased with age in the proximal urethra (P = 0.038), distal to the sigmoid flexure (P = 0.013), and in the distal urethra (P < 0.001), but not in the sigmoid flexure (P = 0.056). The effect of the type of probe used was confirmed at the four anatomical sites examined (P < 0.001), with higher values measured using the probe for rectal use. With the probe for external use, the lumen width ranged 0.5‒2.0 mm in the proximal urethra, 0.6‒1.9 mm in the sigmoid flexure, 0.7‒2.0 mm distal to the sigmoid flexure, and 0.7‒2.1 mm in the distal urethra. With the probe for rectal use, the values were 0.6‒2.3, 0.8‒2.2, 0.7‒2.1, and 0.8‒2.5 mm, respectively. Ultrasound examination of the penile urethra of Dorper × Santa Ines lambs is feasible, and the values obtained for lumen width can be accepted as a parameter for comparison. This examination can be performed using a linear probe for rectal use in large animals.