Congenital Preputial Stenosis
Congenital preputial stenosis will prevent extension of the penis, but 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 preputial skin and the epithelial surface of 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 by young bulls. Until the 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 15.1a). The attachment will often spontaneously regress in affected bulls if allowed 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 15.1b and c).
Figure 15.1 (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.
Source: Courtesy of Robert L. Carson and Dwight Wolfe.
Young bulls at times tear the epithelial attachment prematurely, and hemorrhage into the space between the penile and preputial epithelium results in a localized hematoma. Such injuries may go unnoticed and are often self‐limiting [10]. If bacteria gain access to the damaged tissues and associated hematoma, abscess formation and fibrosis may compromise the ability to extend the penis. Case management should emphasize isolation from other animals to discourage sexual role‐playing during the healing period, accompanied by broad‐spectrum antibiotic treatment to minimize complications. Drainage of an abscess in this location is difficult and must be done with care to minimize loss of the elastic layers of the prepuce.
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 penis to the attachment of the preputial epithelium near the base of the free portion. Like the epithelial connection between the penis and prepuce, this band of tissue normally separates under the influence of androgen exposure as the bull matures. Unlike the epithelial tissues joining the penis and prepuce, the frenulum often contains a large vein. When the process of normal separation fails, the frenulum may persist after breakdown of the other epithelial attachments and result in a band of epithelium and connective tissue joining the tip of the penis with the preputial epithelium at the junction of the prepuce and free portion of the penis (Figure 15.2). 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 preservice breeding soundness examination [11], but occasionally is not detected until bulls attempt natural service.
Figure 15.2 Persistent frenulum. The presence of the persistent frenulum was noted at the time of a post‐purchase breeding soundness examination. A satisfactory pre‐purchase “semen test” had been provided at the time of sale, emphasizing the importance of examination of the external genitalia during a bull breeding soundness examination.
Source: Image courtesy of Dr. Clint Hilt.
The cause or causes of failure of separation of the preputial epithelium and/or frenulum are unknown. An unproven genetic association is suspected [12, 13]. Surgical transection of the frenulum is curative [13, 14], but limiting affected animals to use 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, excessive preputial skin, and a large preputial orifice, and bulls of this phenotype are predisposed to preputial trauma at the time of breeding. While Bos taurus breeds have less redundant skin in the area of the prepuce and are less likely to sustain breeding‐associated preputial trauma, preputial injury at the time of the ejaculatory lunge may occur in any breed.
Preputial Laceration
Bulls with a pendulous sheath and excessive preputial skin may traumatize the preputial tissues independent of the breeding act, but 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 inadvertently trapped between the abdomen of the bull and the bony pelvis of the female at the time of intromission, compressive forces generated at the time of the ejaculatory lunge can injure the entrapped tissues. With mild injury, the preputial epithelium remains intact and the accumulation of edema in the damaged tissues results in an uncomplicated preputial prolapse. More serious injuries result when compression of the entrapped prepuce disrupts the epithelium, with subsequent exposure and damage of the underlying elastic tissues. Commonly referred to as preputial laceration, the injury is in reality the result of bursting of preputial tissues in response to compressive force [15].
Preputial lacerations initiated during the breeding act are predictably located on the ventrum of the prepuce, with the initial disruption of the preputial tissues oriented longitudinally, parallel to the long axis of the bull's body. Following the injury, the disrupted tissues at the site of the injury become oriented transversely as the penis is retracted and the damaged preputial tissues are drawn toward the preputial orifice. As a result, the defect becomes oriented transversely (Figure 15.3). When the damaged 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 a characteristic “elephant trunk” appearance of the prolapsed tissues (Figure 15.4).