Examine the penis and prepuce of bulls from a distance followed by manual examination with the bull safely restrained in a chute with a drop side. The conformation of the sheath is important and the distal end of the sheath should be no longer than a line drawn from the hock to the carpus. The distal end of the sheath, the preputial orifice, should not be excessively large and the angle of the sheath should roughly approximate a line drawn along the ventral aspect of the sheath that intersects the lower front leg or foot¹ (see Figure 17.1).

With the bull in a chute, apply moderate pressure on the bull’s sides with the chute squeeze mechanism and place a sturdy bar behind him to limit his ability to kick during the examination. The preputial hairs should be free of calculi, exudate, or hemorrhage. The penis and prepuce should be contained within the sheath, although naturally polled bulls may have a slight prolapse of the prepuce when they are relaxed. Palpate the entire penis through the sheath for swelling or fibrous tissue.¹

With the aid of an assistant manually extend the penis, grasp the free portion of the penis with a dry surgical sponge, and complete penile extension. The skin of the penis should be moist and pink with no evidence of swelling, vesicles, pustules, papillomas, lacerations, or scar tissue.

Juvenile penile conditions

Penile fibropapilloma

Etiology

Fibropapilloma or warts caused by bovine papilloma virus are fairly common in young bulls. The virus is believed to enter the penile skin through wounds or abrasions sustained during homosexual activity among young bulls. The virus causes neoplastic growth of fibroblasts that is not locally invasive or metastatic. Often several bulls in a group will develop penile fibropapillomas and affected bulls frequently do not have obvious lesions on other parts of the body. Other neoplastic growth on the bovine penis is extremely rare.²

Diagnosis

Bulls with penile fibropapilloma are usually 1–3 years of age and frequently the earliest sign of the lesion is scant hemorrhage from the preputial cavity following attempted coitus. Often the lesion is first noted when the bull is observed masturbating or is presented for semen collection or breeding soundness examination. The growths are typically single pedunculated masses near the glans penis (Figure 18.1), although multiple or sessile growths occasionally develop (Figure 18.2). Very large lesions may prevent complete retraction of the penis into the preputial cavity. Rarely, continued growth of the lesion with the penis retracted into the preputial cavity may prevent penile extension resulting in phimosis.

Penile fibropapillomas are usually easily removed with the bull restrained on a tilt table or in a squeeze chute.¹ Manually extend the penis and either place a towel clamp under the dorsal apical ligament (Figure 18.3) or a gauze tourniquet around the penis proximal to the growth to aid in holding the extended penis. Prepare the surgical field and infiltrate 2–4 mL of 2% lidocaine subcutaneously across the dorsum of the penis proximal to the lesion (Figure 18.4). Repeat the surgical preparation and carefully identify the urethra to avoid incising this tissue during excision of the growth. Catheterize the urethra with a 10-French male dog urinary catheter to help identify the urethra and thus avoid this structure (Figure 18.5). Dissect the skin of the penis at the base of the lesion until the growth is completely removed. In lieu of sharp dissection with a scalpel, judicious dissection with a CO₂ laser may assist hemorrhage control. Large growths are more easily removed by gradually debulking the lesion until the entire mass is removed. Ligate any small vessels and close the skin with #0 absorbable suture (Figure 18.6). Very small growths may be excised without anesthesia or suture closure. Remove the towel clamp and return the penis to the preputial cavity. Application of topical or systemic antimicrobials is optional.

Postoperative care

Penile fibropapilloma may recur since new growth can occur if the bull is an active state of disease. Complete removal of the growth with an adjacent margin of unaffected penile surface epithelium lessens the likelihood of recurrence. Commercial or autogenous wart vaccine has been suggested to prevent or reduce recurrence of the lesions. Anecdotal evidence suggests the use of Immunoboost (Bioniche Animal Health, USA) may help prevent recurrence of penile lesions. Bulls treated for penile fibropapilloma should be examined for healing or regrowth 4 weeks following surgery before entering breeding service.

Penile hair rings

Body hair may accumulate on the penis of young bulls during homosexual riding and may develop an encircling ring on the penis of the more aggressive bull¹ (Figure 18.7). The encircling ring may become sufficiently tight to cause pressure necrosis with damage to the urethra causing urethral fistula formation. In severe cases the constricting ring may cause avascular necrosis of the surface epithelium of the penis and in the most severe cases damage the dorsal nerves of the penis or slough the entire glans penis. Treatment involves removal of the encircling ring of body hair and topical application of an emollient antibacterial agent. If a urethral fistula has formed, surgical repair may be necessary to restore breeding soundness.

Persistent frenulum: delayed preputial–penile separation

The penis of the bull calf cannot be extended prior to puberty due to interdigitating attachment of the skin of the penis and prepuce and lack of a sigmoid flexure. During puberty androgen production shifts from androstenedione to testosterone, and the attachment of the penis and prepuce begins and should be complete between 8 and 11 months of age. Young bulls are occasionally presented with incomplete separation at 12–14 months of age.^1,3 In these bulls separation can be completed by pulling the prepuce back from the free portion of the penis. These tissues should separate easily and hemorrhage is seldom a problem.

The penile frenulum is a thin band of connective tissue on the ventral midline of the free portion of the penis which adjoins the prepuce. Normally the frenulum ruptures during penile separation from the prepuce. When the frenulum does not rupture, the penis extends but the frenulum causes ventral bending of the distal penis during extension (Figures 18.8, 18.9 and 18.10). Surgical repair is relatively simple. I recommend ligating each end of the frenulum and transecting the tissue to reduce the possibility of hemorrhage, although not all practitioners adhere to this practice (Figures 18.11, 18.12 and 18.13) The owner should be advised that this condition is considered to be heritable and retaining the bull’s sons as sires is not recommended (see also Chapter 17).

Anatomy and physiology of erection

Erection in the bull occurs when blood flow increases in the deep artery of the penis and into the crus penis and subsequently into the corpus cavernosum penis (CCP) following olfactory or visual sexual stimulation.^4–6 The CCP in the bull is a closed system in that erectile blood flows into the penis from the crus and leaves this same area during detumescence following erection. The stimulation that causes this reflex dilation of the deep artery of the penis also causes relaxation of the retractor penis muscles which hold the penis in the preputial cavity. As the retractor penis muscles relax, the sigmoid flexure relaxes and the mildly engorged penis protrudes from the sheath.^6–8 With continued sexual stimulation the ischiocavernosus muscles begin rhythmic contraction that raises blood pressure from the normal resting state of 15 mmHg within the CCP. Peak pressure within the CCP may be greater than 14 000 mmHg (1.87 MPa). This rapid increase in blood pressure within the CCP causes complete penile extension and erection. Following ejaculation the ischiocavernosus muscles relax, detumescence occurs as blood pressure within the CCP decreases, and the penis is withdrawn back into the preputial cavity.⁸

Erection may be induced in the bull with an ejaculator, although the optimal method for evaluating erection is with observed test mating. Normal function of the penile nerves is essential for coitus and is most accurately assessed by observed test mating or by semen collection using an artificial vagina.^9,10

Test mating

Bulls with erectile dysfunction do not achieve sufficient erection pressure to complete coitus.^11,12 Bulls with nerve dysfunction mount the cow but there are no penile searching motions near the vulva and the bull fails to make intromission.^9,10 Usually the penis is placed along the cow’s hip or below the vulva in the escutcheon area above the cow’s udder (Figure 18.14).

Diagnosis of CCP fistulas or vascular shunts (cavernosography)

Contrast radiography of the CCP, known as cavernosography, may confirm vascular defects in the penis.^11–14 Although the procedure may be performed with the bull in a squeeze chute, the technique is more easily accomplished with the bull restrained on a table in lateral recumbency. Manually extend the penis and place a towel clamp under the dorsal apical ligament approximately 5 cm from the distal end of the penis to aid in manipulation of the penis during the procedure (Figure 18.15). Place a length of umbilical tape through the rings of the towel clamp to allow complete removal of the hands from the radiographic field during the procedure (Figure 18.16). Place a double strand of heavy suture (0.6 mm) through the skin of the sheath, between the retractor penis muscles and the penis, and through the skin on the opposite side of the sheath (Figure 18.17). This suture serves to retract the penis away from the abdominal wall to enhance visualization of the sigmoid flexure of the penis.

With the penis fully extended, insert a 16-gauge 3.8-cm needle at a 45° angle proximally through the skin and tunica albuginea and into the CCP. Place the needle on the dorsum of the penis near the towel clamp. To ascertain that the needle has penetrated the tunica albuginea and the tip is within the CCP inject 10 mL sterile saline which should flow into the CCP with ease. Attach a sterile extension set to the needle for ease of injection and to position the hands away from the radiographic field (Figure 18.18). Place a radiographic cassette under the penis, then inject 15 mL of water-soluble radiographic contrast media (Renograffin 76, Squibb Diagnostic, New Brunswick, NJ) and expose the film. Slowly inject an additional 15–30 mL of media as the radiographic series is performed. Remove the cassette and quickly place another cassette more proximal under the penis. By using 43-cm cassettes the entire penis up to the sigmoid flexure may be radiographed with two or three exposures (Figure 18.19). Ideally all radiographic exposures should be completed within 60 s.

There are no vascular communications from the CCP to peri-penile vasculature in the normal penis, and there should be no contrast media outside the CCP (Figure 18.20). A vascular shunt is identifiable as contrast media exiting the CCP (Figures 18.21 and 18.22).

Congenital vascular shunts: erection failure due to corpus cavernosal shunts (impotentia erigendi)

Occasionally young bulls fail to achieve intromission due to congenital corpus cavernosal vascular shunts. These bulls usually are normal on physical examination but fail to achieve adequate intracorporeal pressure for erection. When observed during erection, either by test mating or with electroejaculation, the free portion of the penis becomes noticeably bluish during attempted erection. The bluish discoloration is due to blood from a relatively porous tunica albuginea of the penis exiting the CCP and being removed by subcutaneous capillaries and veins. These shunts may be confirmed by cavernosography (Figure 18.23). Typically the shunts are multiple and not considered repairable.

Hematoma of the penis

The term “hematoma of the penis” is used to indicate rupture of the tunica albuginea of the penis, an injury that happens much more frequently in bulls than other farm animals and may lead to permanent infertility. Common terms for this condition are broken or fractured penis.^1,15–17

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