Inability to Breed due to Injury or Abnormality of the External Genitalia of Bulls

Chapter 14
Inability to Breed due to Injury or Abnormality of the External Genitalia of Bulls

Herris Maxwell

Department of Clinical Sciences, College of Veterinary Medicine, Auburn University, Auburn, Alabama, USA


Impotence, the inability to sire offspring, may be due to abnormalities in sperm production and/or inability to copulate. Inability to copulate is further divided into inability to perform the copulatory act due to physical limitations or inability to copulate due to erection failure. This chapter reviews important causes of impotence due to abnormalities of the genitalia of the bull. Abnormal spermatogenesis is covered in other chapters of this book.


Natural service typically utilizes bull to cow ratios of 1 : 15 to 1 : 50.1 In single-sire units inability of the bull to breed will have a devastating effect on reproductive efficiency. Similarly, when a socially dominant bull in a multi-sire unit is unable to complete the copulatory act, the decrease in breeding efficiency may not be masked by the presence of additional subservient bulls. Although artificial insemination eliminates the requirement for coitus, semen must be collected from the bull and most semen processed for the artificial insemination industry is collected by methods that utilize an artificial vagina (AV) as the bull mounts a teaser or phantom to mimic the copulatory act. While some impediments to the copulatory act may be overcome by the collection of semen using electroejaculation, others may not be easily managed.

Physiology of erection in the ruminant

The unique and interesting features contributing to extension and erection of the penis of the bull have been described.2,3 A brief summary of the process follows.

The fibroelastic ruminant penis is encased in the rigid tunica albuginea. The erectile tissues of the corpus cavernosum penis (CCP) and corpus spongiosum penis (CSP) are contained within this strong, relatively inelastic case. In the nonerect state the penis is maintained within the prepuce and sheath and assumes a sigmoid shape due to the traction of the retractor penis muscles, which insert on the ventral surface of the mid-shaft of the penis at the distal bend of the sigmoid flexure. The proximal terminus of the CCP is the bulb of the penis, which divides into two crura that attach to the ischiatic arch on either side of the pelvis and are covered by the ischiocavernosus muscles.

At the initiation of sexual arousal the retractor penis muscles relax in synchrony with increased blood flow from the deep arteries of the penis into the crura and the CCP fills with blood. The lack of tension from the retractor muscles coupled with complete filling of the CCP initiates partial straightening of the sigmoid flexure. Contractions of the ischiocavernosus muscles force the crura against the pelvis and occlude all vascular flow to and from the CCP resulting in a closed hydraulic system. Further rhythmic contractions of the ischiocavernosus muscles apply pressure to the blood contained within the crura and this pressure is transferred to the blood contained within the CCP to generate the pressure necessary for full erection and extension of the penis. The pressure generated in the CCP far exceeds the arterial pressure of the circulatory system, reaching 14 000 mmHg (1.87 MPa) or higher at the time of peak erection.4


Although brief, the breeding act requires orchestration of interrelated simple and complex events. The bull must identify the female in estrus, approach, extend the penis, mount appropriately, achieve full erection, adjust his stance and posture while locating the vulva with the penis, achieve intromission, make the breeding lunge, ejaculate, and dismount. The physical requirements are obvious and structural soundness is a necessary component of the successful breeding act. In cattle the coital act occurs rapidly, with time from mounting to intromission and ejaculation generally less than 10 s and the time from intromission to ejaculation 1–2 s.5,6 Although some false mounts are expected, excessive numbers may be associated with pathology of the axial or appendicular skeleton or may indicate problems with the erection process, impediments to penile protrusion and extension, or lack of innervation of the glans penis.

Following a successful breeding attempt the bull has a brief refractory period, the length of which varies among bulls and is likely affected by age, physical condition, and the presence of other bulls and females exhibiting estrus. For young structurally sound bulls the refractory period may be only a few minutes and many bulls can be expected to copulate multiple times per day.

Abnormalities of the prepuce

The prepuce is an invagination of abdominal skin that contains the free portion of the nonerect penis and covers the body of the penis behind the glans. The penile attachment of this invagination of skin occurs caudal to the glans penis and in the nonaroused state results in the formation of a fornix in the preputial cavity adjacent to the free portion of the penis. The preputial orifice is located caudal to the umbilicus and is surrounded by a tuft of long hair that serves to divert urine away from the skin surrounding the orifice following micturition. When erect, the free portion of the penis extends beyond the preputial orifice and the hairless reflection of skin within the preputial cavity extends with the penis and covers the shaft. The subcutaneous tissues of the prepuce must be freely moveable to allow extension and retraction of the penis and the preputial reflection and these specialized connective tissues are referred to as the elastic layers of the prepuce.

Congenital and developmental anomalies of the prepuce

Congenital preputial stenosis

Although congenital preputial stenosis could prevent extension of the penis, stenosis secondary to injury or laceration of the preputial tissues is more common.

Incomplete separation of the penile and preputial epithelium

Prior to puberty, the epithelium of the free portion of the juvenile penis and the integumentary epithelium of the penile portion of internal lamina of the prepuce are joined by an interdigitating attachment.7–9 Exposure to the trophic effects of androgens as bulls approach puberty leads to an increase in penile size and to development of the sigmoid flexure characteristic of ruminants. Simultaneous with the increase in penile size, the epithelial attachments between the prepuce and the free portion of the penis weaken and begin separating. Separation may be facilitated by mounting activity and early attempts at erection during sexual role-playing in young bulls. Until this separation is complete at 8–11 months of age, extension of the penis is not possible.7,8,10

Normal separation is sometimes delayed and may result in an inability to fully extend the penis at the time of a breeding soundness examination or during an observed breeding attempt (Figure 14.1). The attachment will spontaneously regress in most bulls given adequate time to mature but assisted separation by gentle application of manual traction to the penis is sometimes advocated in cases where partial separation has already occurred (Figure 14.1b,c).


Figure 14.1 (a) Failure of separation of the epithelium of the free portion of the penis and the penile portion of the prepuce. (b) Note the adherence between the preputial and penile skin. Application of gentle traction to the penis to facilitate adherence breakdown. (c) Penile and preputial epithelium following breakdown of the epithelial adherence.

Courtesy of Robert L. Carson and Dwight Wolfe.

Young bulls sometimes tear the epithelial attachment prematurely and hemorrhage into the epithelium, resulting in formation of a localized hematoma. Such injuries may go unnoticed and are often self-limiting.10 Should bacteria gain access to the damaged tissues and hematoma, the formation of an abscess may result in phimosis if the bull’s ability to extend the penis is compromised. Case management should emphasize isolation from other animals to discourage sexual role-play accompanied by broad-spectrum antibiotic treatment to minimize complications.

Persistent frenulum

The frenulum is a thin band of tissue found in juvenile bulls that extends from the midline of the ventrum of the tip of the free portion of the penis to the attachment of the preputial epithelium near the base of the free portion. Similar to the epithelial connection between the penis and prepuce, this band of tissue normally separates as the bull matures. Unlike the epithelial tissues of the penis and prepuce, the frenulum often contains a large vein. When the process of normal separation fails, the frenulum may persist and the result is a band of epithelium and connective tissue joining the tip of the penis with the preputial epithelium near the junction of the prepuce and free portion of the penis (Figure 14.2). A persistent frenulum results in a sharp ventral bend of the distal penis as it becomes erect. Persistent frenulum is often detected in young bulls during a routine pre-service breeding soundness examination,11 but occasionally is not detected until the bull attempts natural service.


Figure 14.2 Persistent frenulum. The location on the ventral surface of the penis adjacent to the median raphe is typical. Note the accumulation of hair between the penis and the frenulum.

Courtesy of Jack Smith.

The cause or causes of failure of separation of the preputial epithelium and/or frenulum are unknown. Although unproven, a genetic association is suspected in some breeds.12,13 Surgical transection of the frenulum is curative13,14 but use of affected animals only as terminal sires is recommended.

Injuries to the prepuce

Bulls sometimes sustain injuries to the prepuce severe enough to interfere with breeding. Bulls from breeds with substantial Bos indicus influence have a pendulous sheath and excessive preputial skin accompanied by a large preputial orifice and bulls with this phenotype are predisposed to preputial trauma at the time of breeding. Bos taurus breeds are less predisposed to preputial trauma but preputial injury at the time of the ejaculatory lunge may occur in any breed.

Preputial laceration

Although bulls with a pendulous sheath and excessive preputial skin may traumatize the preputial tissues independent of the breeding act, most serious preputial injuries occur at the time of the ejaculatory lunge. As the free portion of the penis enters the vagina during coitus, preputial skin slides caudally up the shaft of the penis toward the abdomen of the bull and folds of redundant skin gather at the preputial orifice. This “bunching” of preputial skin usually occurs without incident, but when preputial tissue is trapped between the abdomen of the bull and the bony pelvis of the female at the time of intromission compressive forces generated by the ejaculatory lunge can be focused on the entrapped tissues. In mild cases the preputial epithelium remains intact and the accumulation of edema in the damaged tissues results in an uncomplicated preputial prolapse. More serious injury occurs when compression of the entrapped prepuce disrupts the epithelium, with subsequent exposure and damage of the underlying elastic tissues. Although commonly referred to as preputial laceration, the injury is actually the result of bursting of preputial tissues in response to compressive force.15

Preputial lacerations initiated during the breeding act predictably occur on the ventrum of the prepuce, with the initial injury in the preputial tissues oriented longitudinally, parallel to the long axis of the bull’s body. Following the injury, as the penis is retracted the damaged preputial tissues are drawn toward the preputial orifice and the disrupted tissues at the site of the laceration fail to maintain normal alignment. As a result, the defect becomes oriented transversely (Figure 14.3). If the preputial tissues cannot be retracted through the preputial orifice, the transverse orientation of the lacerated tissues results in shortening of the caudal aspect of the exposed prepuce and the characteristic “elephant trunk” appearance of the prolapsed tissues (Figure 14.4).


Figure 14.3 Preputial laceration in a breeding bull. The laceration assumed a transverse orientation as the preputial tissues were retracted toward the preputial orifice.


Figure 14.4 Preputial laceration with prolapse of the damaged preputial tissues. Reorientation of the wound results in the elephant trunk appearance of the prolapsed preputial tissue.

Trauma and disruption of the preputial epithelium and underlying elastic tissues result in inflammation and edema and the open wound inevitably becomes septic. As dependent edema in the prolapsed tissues increases the size and weight of the externalized prepuce, traction on the prepuce results in increasing amounts of preputial tissue becoming exposed. Additional trauma, mutilation, or desiccation of the unprotected preputial tissues complicates wound management and treatment. Wound contracture at the site of the injury further distorts the tissues as the reoriented wound undergoes fibrosis (Figure 14.5).


Figure 14.5 Wound contracture and fibrosis at the site of a preputial laceration.

Courtesy of Richard Hopper.

The preputial retractor muscles serve to elevate the prepuce and this elevation can minimize edema formation in damaged tissues. Because many polled bulls lack retractor prepuce muscles, preputial prolapse following laceration in naturally hornless bulls tends to become more severe.16

Wolfe and Carson have constructed a four-point classification scheme that incorporates the severity of the preputial injury to estimate the prognosis for return to function and guide treatment decisions (Table 14.1).

Table 14.1 Classification of preputial prolapse.

Source: Wolfe D, Beckett S, Carson R. Acquired conditions of the penis and prepuce (bulls, rams, and bucks). In: Wolfe DF, Moll HD (eds) Large Animal Urogenital Surgery. Baltimore: Williams and Wilkins, 1998, p. 258.

Category Description Treatment and prognosis
I Simple preputial prolapse with slight to moderate edema without laceration, necrosis, or fibrosis Either conservative or surgical treatment with good prognosis
II The prolapsed prepuce has moderate to severe edema, may have superficial lacerations or slight necrosis but has no evidence of fibrosis Surgery is the usual course of therapy with a good to guarded prognosis
III There is severe edema of the prolapsed prepuce with deep lacerations, moderate necrosis, and slight fibrosis Surgery is indicated and the prognosis is guarded
IV The prolapsed prepuce has been exposed for quite some time and has severe edema, deep lacerations, deep necrosis, fibrosis, and often abscess Surgery and salvage by slaughter are the only options, and a guarded to poor prognosis follows surgery

Medical management of preputial laceration and prolapse is aimed at control of sepsis, reduction of edema, and eventual return of the damaged tissues to the preputial cavity. Application of emollients to prevent desiccation and topical antibiotics should be combined with light bandaging. Careful cleansing and flushing of the wound with dilute antiseptic solutions combined with debridement of devitalized tissues is necessary. Topical antibiotic therapy is usually sufficient if wound management is adequate. Bandaging of the exposed preputial tissues must be done carefully to avoid restricting blood flow and devitalizing tissues but proper application of a circumferential bandage to prevent desiccation and to apply mild compression is useful. To apply a bandage following cleansing and application of an emollient antibiotic ointment, first place a short length of latex tubing into the preputial orifice and position it with one end in the preputial cavity proximal to the torn epithelial tissues and the other end exiting the preputial orifice to allow urine egress from the prepuce. Then place a piece of clean 5-cm orthopedic stockinette over the exposed preputial tissues and snugly apply an elastic tape bandage over the stockinette, prepuce, and urine egress tube beginning at the distal end of the prolapsed tissue, overlapping the tape as it advances up the prepuce to the preputial orifice where it can be secured to the haired skin of the sheath (Figure 14.6). Following bandaging, the edematous prepuce may be suspended by application of a bib or sling made of net material or burlap supported by straps encircling the bull’s abdomen (Figure 14.7). Frequent bandage changes are necessary and the wound should be treated locally each time it is exposed. Cold water hosing for 10–15 min at each bandage change will reduce edema and remove necrotic debris. With diligent treatment many bulls may be returned to service without surgery17 but repeat injury is common.


Figure 14.6 Bandaging of the prolapsed preputial tissues following application of an emollient and topical antibiotics. Placement of a urine egress tube to evacuate urine from the prepuce, a light stockinette to protect the exposed tissues (a), and an overlapping elastic tape pressure bandage secured to the preputial hairs and urine egress tube distally and to the skin of the haired sheath proximally (b).


Figure 14.7 Burlap “bib” applied to the bull’s abdomen to suspend the edematous preputial tissues.

Surgical treatment following preputial laceration can improve outcome18 and is indicated when the bull’s value and remaining breeding life is sufficient to justify the expense.18,19 Surgery must always be preceded by preoperative wound management. Excellent descriptions of the surgical options appear elsewhere in this book (see Chapter 17).

Retropreputial abscess

Preputial injury and laceration are not limited to Bos indicus influenced breeds. In Bos taurus bulls preputial injury may occur at the time of breeding in a manner identical to that described for Bos indicus bulls but the outcome is often altered by phenotype. Bos taurus breeds are more likely to retract all the damaged tissues into the preputial cavity following injury and as a result the wound is less likely to be noticed early. The compromised elastic tissues within the preputial cavity are contaminated with bacteria and cellulitis and phlegmon rapidly develop and often progress to abscess formation. The preputial swelling may be confined to a well-defined area adjacent to the sheath, or may be more diffuse and occasionally extend from the preputial orifice caudally toward the scrotum.

Retropreputial abscess formation is more likely in bulls of Bos taurus than Bos indicus influenced breeds due to lack of redundant skin and generally tighter sheath conformation. Affected bulls present with an obvious swelling visible through the overlying skin of the sheath that may be accompanied by the presence of pus or blood at the preputial orifice. Diagnosis is based on physical examination and palpation, sometimes augmented by ultrasound imaging of the tissues. This condition must be differentiated from the enlargement of the elastic tissues seen following rupture of the tunica albuginea of the penis. In contrast to the lesion seen with rupture of the tunica albuginea, retropreputial abscesses are generally nonsymmetrical and located distal to the sigmoid flexure nearer the level of the preputial fornix (Figure 14.8). Retropreputial abscess formation carries poor prognosis for future breeding. Destruction and impairment of the elastic tissues frequently result in adhesion formation within the elastic tissues of the prepuce and the overlying skin or in compromise of the diameter of the preputial lumen, either of which may prevent extension of the penis.20


Figure 14.8 Retropreputial abscess following preputial laceration in a young bull. Note location of the swollen tissues in the distal sheath.

Therapy for retropreputial cellulitis, phlegmon, and abscessation relies on systemic antibiotic administration and local wound management. Daily flushing of the preputial tissues with dilute antiseptic solutions and cold water hosing of the sheath aids in resolution of cellulitis. Drainage of a retropreputial abscess into the preputial lumen at the site of the original injury is difficult but if possible may facilitate recovery. No attempt should be made to drain a retropreputial abscess through the overlying skin of the sheath as damage and sepsis of the underlying elastic tissues is inevitable and formation of peri-penile adhesions will decrease the chance of a successful outcome.17,20 Even with aggressive therapy the prognosis is guarded to poor and many affected bulls will never return to service.20


Phimosis, the inability to extend the penis, effectively prevents the bull from breeding and may be diagnosed at the time of an observed breeding or by induction of erection with an electroejaculator. Phimosis may be due to stenosis of the preputial opening or lumen, adhesions within the elastic layers of the prepuce and surrounding skin, or occasionally to abnormalities of the distal penis including the presence of large penile fibropapillomas.

Stenosis or stricture of the preputial lumen can occur following preputial injury despite appropriate and apparently successful medical or surgical management. Scar tissue replaces damaged elastic tissues and contracture and cicatrix formation may constrict the preputial lumen and result in preputial stenosis sufficient to prevent extension of the penis (Figure 14.9). If circumferential constriction of the preputial cavity occurs distal to the end of the tip of the nonerect penis, sexual arousal and engorgement of the penis will force the distal portion of the penis down the prepuce until the constriction is encountered and the preputial lamina will be forced out the preputial orifice without exposure of the free portion of the penis. Strictures sometimes interfere with the evacuation of urine from the preputial cavity. Noncircumferential scar formation at the site of a healed preputial laceration may also compromise the preputial lumen enough to prevent penile extension.


Figure 14.9 Phimosis due to circumferential stricture of the preputial cavity following preputial laceration.

Courtesy of Craig Easley.

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Aug 24, 2017 | Posted by in GENERAL | Comments Off on Inability to Breed due to Injury or Abnormality of the External Genitalia of Bulls

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