Chapter 16 Dwight F. Wolfe Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA The scrotum of the bull is a dependent appendage of the ventral abdominal skin that supports and protects the testicles and helps regulate testicular temperature. The testis is an abdominal organ maintained 2–7 °C cooler than body temperature.1 Testicular thermoregulation is a complex process that includes contraction of the tunica dartos within the scrotal wall to alter scrotal surface area in concert with the cremaster muscles to regulate the distance of the testicles from the body. The scrotum is one of the few places in the bovine where sweat glands are found. Blood temperature is regulated by counter-current heat exchange in the pampiniform plexus just proximal to the testicle between the testicular artery and vein. These mechanisms collectively function to maintain testicular temperature 4–6 °C below core body temperature, which is optimal for normal semen production.1,2 Bulls with scrotal or testicular disease or injury frequently have scrotal enlargement, which may be unilateral or bilateral and can be caused by a variety of conditions.2,3 It is important to use both visual and palpable information to determine the source of the swelling and make a definitive diagnosis. The most common cause of scrotal enlargement in the bull is fluid accumulation within the vaginal cavity.3 Fluid accumulation is usually unilateral and may be due to periorchitis, hydrocele, or hematocele. Appreciable fluid accumulation is readily detectable by palpation of the testis; the consistency of the fluid may be thin and easily displaced by palpation, or thicker (e.g., purulent material or clotted blood) which may be confirmed by ultrasound. Additionally, fibrinous or fibrous adhesions may form between the testis or epididymis and parietal vaginal tunic and these may be detected by palpation as the testis is moved within the vaginal cavity. Orchitis is usually subclinical but rarely may range to severe and perhaps suppurative.4,5 The dense fibrous tunica albuginea surrounding the testicle limits this organ’s potential for enlargement and therefore there is usually not significant testicular swelling. Although orchitis may affect one or both testes, greater than 25% size difference between the two testes should be considered abnormal. Orchitis in the bovine is usually due to hematogenous spread of bacteria but in rare cases may be due to puncture wounds through the scrotum. Occasionally, traumatic testicular rupture may occur and is diagnosed by an amorphous clot-like consistency by palpation and confirmed by ultrasound. Epididymitis occurs more commonly than orchitis in bulls and may be diagnosed by thorough examination of the testes and scrotal contents.6–8 The condition is often unilateral in the bull and may present as a swollen painful epididymal tail in the acute phase of the disease. Chronic epididymitis usually results in epididymal tails that are small and firm, and infertility is often caused by their eventual obstruction. Periorchitis – inflammation of the peritesticular tissues with fluid accumulation and adhesions – frequently accompanies epididymitis or orchitis. Trauma is a common cause of pathological changes in scrotal contents. Trauma to the scrotum may produce hematocele (hemorrhage into the vaginal cavity) or hydrocele (accumulation of inflammatory exudate or transudate in this cavity).3 Trauma severe enough to damage the tubular integrity of the testicle or epididymis may lead to an autoimmune reaction due to the extravasated haploid sperm that produce granulomatous reactions. Swelling of the wall of the scrotum can usually be differentiated from other causes of scrotal enlargement by palpation of the thickened scrotal skin, presence of pitting edema, with confirmation by ultrasound (Figure 16.1). Generalized swelling of the scrotal wall may be caused by infection with Mycoplasma wenyonii9,10 (Figure 16.2). This condition is not treated surgically but should be considered when managing scrotal wall thickness. Crushing or blunt trauma to the scrotal wall may disrupt the normal muscular and vascular architecture of the scrotal wall with resultant increased wall thickness. If these injuries are severe and unilateral, removal of the affected half of the scrotum and its associated testicle may be warranted. Figure 16.1 Pitting edema of the scrotal wall. Figure 16.2 Generalized edema of scrotal wall due to Mycoplasma weyenoii. Primary testicular tumors are not common in bulls but unilateral or bilateral scrotal enlargement has been reported in bulls with mesothelioma.4,5,9,11 Carefully examine the scrotum for dermatitis, edema, scar tissue, and symmetry.2 Palpate the testicles for relative size, firmness, symmetry, evidence of pain or swelling, presence of fluid in the vaginal cavity, and the ability of the testicles to move freely within the vaginal cavity. There should be no more than 10% difference in the size of the testes and normal testicular tone approximates that of liver. Scrotal circumference is heritable and highly correlated with daily sperm output, sperm reserves, serving capacity, and age of puberty of the bull’s offspring. Measure the scrotal circumference with a nonelastic tape at the widest circumference of the scrotum (Figure 16.3). This measurement can be compared against normal values that are readily available in tables for scrotal circumference in different age bulls. However, the recommended minimum scrotal circumferences from the Society for Theriogenology bull breeding soundness evaluation serve as an excellent reference:12 Figure 16.3 Scrotal circumference measurement.
Surgery of the Scrotum and its Contents
Normal scrotum and testes
Diagnosis of testicular disease or injury
Physical examination of the scrotum and testicles
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