Ultrasound Evaluation of the Reproductive Tract of the Bull

Chapter 9
Ultrasound Evaluation of the Reproductive Tract of the Bull

Harry Momont and Celina Checura

Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, USA


Diagnostic ultrasound has become the standard for medical imaging of soft tissue. The genital tract is an obvious target for this diagnostic modality and while ultrasound is routinely employed for evaluation of the female genital system, its use in male domestic animals remains much less common. In the bull, for example, the routine breeding soundness evaluation (BSE) as recommended by the Society for Theriogenology does not include ultrasonographic assessment of the genital system.1 In most cases of infertility in the bull, adequate diagnostic and prognostic information is obtained without the use of ultrasonography. A major advantage of ultrasonography, however, is the ability to localize and objectively assess morphologic changes in tissue.

A thorough history, complete physical examination, and a BSE should precede an ultrasound examination of the bull’s genital system. We routinely perform ultrasound evaluations for bulls with palpable or visible abnormalities of the genital system; those with pyospermia, hemospermia, azoospermia, or oligospermia; those with low semen volume; and bulls that persistently produce high numbers of morphologically abnormal or immotile sperm. As with any medical technology, the use of ultrasonography for examination of the bull will expand as veterinarians become more familiar with the modality and its application.

Equipment and general methodology

A wide variety of ultrasound equipment is available for diagnostic imaging. Most veterinary clinics providing service to cattle owners will already have a portable, real-time, B-mode system with a linear intrarectal probe that is used for reproductive examination of cows. All illustrations in this chapter were obtained with this type of system. Typical probe frequencies range from 5 to 7.5 MHz and are more than adequate for imaging the bull’s reproductive tract. More detailed images of the epididymis and penile tissues can be obtained using probes with a smaller footprint and higher frequency. Representative images may be captured, labeled, measured, and saved for inclusion in the medical record. These applications are available with most ultrasound systems. In order to adequately assess a system you intend to purchase, it is advisable to use it in an actual clinical setting so you can critically evaluate functionality and image quality under real-world conditions. Beyond the primary issue of image quality, durability and resistance to damage from dirt and moisture are important considerations when purchasing an ultrasound unit to be used in cattle environments.

Operator safety is always a concern when working with bulls. A chute or stock with a head catch and squeeze option is ideal. For added security, the bull’s head should be secured with a halter. Most bulls will tolerate scrotal, perineal, and rectal examinations with little restraint beyond confinement in the chute. If a kick bar is used behind the bull, extreme caution is needed to avoid placing the arms and hands in a dangerous position. For fractious bulls or for examination of the prepuce and penis cranial to the scrotum, we prefer sedation (xylazine 0.01–0.02 mg/kg i.v.).

While it is beyond the scope of this chapter, a fundamental understanding of ultrasound principles and an appreciation for common image artifacts are essential for anyone offering diagnostic ultrasonography services. For those requiring a more expansive treatment of the basic principles of veterinary ultrasonography, excellent texts are available.2,3 A bovine reproductive anatomy monograph is available from the National Association of Animal Breeders4 and McEntee5 is an excellent resource for those seeking a review of the pathology of the male genital system.

Images are obtained by either a transcutaneous or transrectal scan depending on the anatomical location of the tissue to be examined. If long or dense hair covers the area, the quality of the transcutaneous image is improved by first shaving the skin. Shaving is usually not required for examination of the scrotum and testes. Image quality is enhanced when the scrotal skin is stretched tightly over the testes. To do this, firmly grasp the scrotal neck dorsal to the testes and pull the testes ventrally while conducting the examination. In all cases of transcutaneous ultrasonography, a coupling agent is required to achieve good contact between the probe and skin. Any air or gas between the probe and the tissue to be examined will interfere with the acquisition of an image. The use of ultrasonic coupling gel as a coupling agent has the advantage of long duration, since it does not evaporate. Additionally, it is approved by most manufacturers for contact with the probe surface. Alcohol (70% isopropyl) also makes a good coupling agent, with the advantage that it does not have to be cleaned from the probe or patient after the examination is completed. A disadvantage of alcohol is that it evaporates and often needs to be reapplied to complete the examination. Additionally, not all probe surfaces are approved for contact with alcohol or other solvents. Placing a protective cover containing a small amount of coupling gel over the probe will prevent alcohol from contacting the probe surface. A disposable examination glove works well for this purpose.

For transrectal examination of the pelvic organs, the probe is covered with an examination sleeve containing just enough coupling gel to provide good contact between the probe and sleeve. Most probes designed for transrectal use in horses and cattle will fit snugly within a finger of a glove or sleeve. The feces are evacuated from the rectum and a manual examination is conducted before the covered probe is inserted. In our experience, no coupling agent is necessary to maintain contact between the sleeve and rectal mucosa beyond the lubricant normally used for palpation per rectum. If a protective cover is not used, the probe should be cleaned and disinfected between examinations following the recommendations of the probe manufacturer.

While diagnostic ultrasonography is generally regarded as safe for examination of reproductive tissues and fetuses,3 few published data exist in the veterinary literature. Coulter and Bailey6 exposed yearling beef bulls to ultrasound (3 min for each testis, one time, using a 5-MHz linear transducer) and found no discernible effects on sperm numbers, morphology, or motility during a 70-days period after the examination. They concluded that diagnostic ultrasonography should be safe for examination of the bull scrotum and testes. A reasonable approach is to use the minimum power and contact time necessary to complete your examination.

Examination of the scrotum

B-mode ultrasonography of bull testes was first described by Pechman and Eilts7 in 1987. A thorough visual and manual examination of the scrotum and its contents should always precede the ultrasound examination. The scrotum and testes are then examined by ultrasound in both a sagittal and transverse plane with the probe applied to the cranial, lateral, or caudal surface of the testis depending on the examiner’s preference. A complete examination includes the spermatic cord, the entirety of the testicular parenchyma, the epididymis, and the scrotal wall. The body of the epididymis and the ductus deferens are difficult to detect unless they are grossly abnormal.

Normal ultrasonic appearance of the testis is shown in Figure 9.1. The testis parenchyma appears as a homogeneous tissue with a stippled medium echogenicity that surrounds the centrally located and more hyperechoic (whiter) mediastinum testis. The mediastinum testis is normally less than 5 mm wide. The parenchyma consists primarily of convoluted seminiferous tubules that contain the sustentacular (Sertoli) and germinal cells but also includes the adjacent interstitial (Leydig) cells along with associated vascular, neural, and stromal tissues. The seminiferous tubules are connected by the straight tubules to the rete testis that comprises a series of interconnected channels within the mediastinum testis. Sperm pass dorsally through the rete testis to the efferent ducts that in turn penetrate the capsule of the testis before uniting as the epididymal duct.


Figure 9.1 Caudal ultrasonographic views of the left testis of a yearling dairy bull. Caudal is at the top and cranial at the bottom of each ultrasound image. On the left is a sagittal view with the mediastinum testes (between arrows in each image) appearing as a more hyperechoic linear structure running through the approximate center of the less echoic testis parenchyma. On the right side of the image is a transverse view of the same testis with the mediastinum in cross-section, again in the middle of the less echoic parenchyma. The scrotal wall is visible adjacent to the probe on the top (caudal) and on the bottom (cranial) of the testis in each image. The bright white line at the bottom of each image is a gas artifact that marks the far side of the scrotal skin.

Changes in the ultrasonic appearance of the testis parenchyma can reflect normal events around puberty as well as pathology. An increase in echogenicity (increased pixel intensity, or a whiter parenchyma) has been reported to occur in association with sexual development around the time of puberty,8,9 but ultrasonography was no better at predicting puberty than was measurement of scrotal circumference.9 While pixel intensity has been correlated with attainment of sexual maturity as assessed by semen quality,10 it seems to be a better predictor of future semen quality than the present status of the bull.11 In any event, objective assessment of these subtle changes in pixel intensity is not possible by real-time visual interpretation of an ultrasound image. To accurately assess pixel intensity, images must be obtained and digitally preserved using rigorously standardized methods. The digital files are then sampled and evaluated using computer software that can objectively assess the gray scale of each pixel in the sampled area, providing both an average intensity and measure of variation. Given the limited clinical utility and the great effort required, Brito et al.9 concluded that “though testicular ultrasonogram pixel intensity might be useful for research purposes, clinical application of this technology in the present form for bull breeding soundness evaluation is not justifiable.”

The majority of the discrete ultrasonographic changes detected in the testis are more hyperechoic than normal tissue. These may appear as small foci scattered throughout the testis (Figure 9.2) or they may be more localized (Figure 9.3). Larger hyperechoic lesions are often seen to radiate from the rete to the periphery of the testis, suggesting the complete involvement of one or more seminiferous tubules (Figure 9.4). The histologic basis for the increase in echogenicity is usually fibrosis12 but the echogenicity itself does not confirm histology or etiology. Tumors are generally more hyperechoic than the normal testis parenchyma (Figure 9.5) but mixed or hypoechoic echogenicity is also possible.3 Mineralized lesions are extremely hyperechoic and are always accompanied by intense or complete shadowing causing a loss of image distal to the lesion (Figure 9.6).


Figure 9.2 Sagittal view of the left testis of a mature bull with small hyperechoic foci distributed throughout the testis parenchyma.

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Aug 24, 2017 | Posted by in GENERAL | Comments Off on Ultrasound Evaluation of the Reproductive Tract of the Bull
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