The use of nonbreeding bulls for estrus detection (described as teaser bulls) is a method of identifying cows in estrus to help facilitate successful artificial insemination. Many strategies are commonly used to render herd members infertile for this purpose, typically by prohibiting intromission or insemination of receptive cows. Reported methods have included testosterone treatment of steers or heifers, preputial translocation, penile fixation, vasectomy, epididymectomy, CCP occlusion, physical occlusion of the preputial orifice, or a combination of these.1–4
The use of estrus-detection bulls offers important advantages over the use of androgenized animals. First, androgen supplementation of heifers and steers for this purpose is currently illegal2; second, the use of bulls for this purpose is associated with an increase in the percentage of cows identified that are truly in estrus with up to 100% identification, compared with 74% identification by intermittent human observation of a herd2; and third, in the authors’ experience, when androgenization of steers for heat detection was legal, estrus-detection bulls functioned successfully in the herd longer than artificially androgenized animals did. The use of these bulls also confers the benefits of reduced handling of hormone-based pharmaceuticals by producers and reduced time and labor associated with processing cattle multiple times. In herds for which estrus synchronization protocols are used, a nonbreeding bull may aid in detecting estrus in dominant females that are not receptive to other cycling females in the herd as well as in females that have short or weak estrus expression.
Estrus-detection bulls that cannot achieve intromission should be preferred, as their use reduces the risk of transmission of venereal diseases, including Tritrichomonas fetus infection.2,5 The sarcomastigophoran protozoa T fetus is an obligate parasite of the reproductive tract of cows and epithelial surface of the penis and prepuce of bulls. Infected bulls are asymptomatic carriers of T fetus and are capable of transmitting the organism to cows during coitus.6 Infection in cows results in endometritis, cervicitis, and vaginitis and can cause embryonic death, abortion, pyometra, fetal maceration, or infertility.6,7 Major economic losses associated with T fetus infection include a smaller number of live calves born, reduced weaning weight as a result of delayed conception, and the cost of culling and replacing infected cattle. A previous simulation model8 suggested that bull infection rates of 20% to 40% result in a 14% to 50% reduction in annual calf production, with important economic ramifications once the disease becomes endemic in a herd. Vaccines can help reduce the severity of clinical signs in infected females, but they do not prevent disease.9 Although nitroimidazoles were historically effective in treating Tritrichomonas spp infections, no effective medications are currently approved for use in cattle in the United States or Canada. Therefore, cattle with a diagnosis of T fetus infection should be culled.9
The use of estrus-detection bulls has seemingly declined in the past several years owing to implementation of hormonal manipulation techniques that allow for timed artificial insemination; however, use of these animals continues to have a place in many herds, and beneficial effects of bull exposure on cow and heifer cyclicity and fertility are well documented. Hornbuckle et al10 reported that the presence of bulls was associated with higher circulating progesterone concentrations and a faster rate of return to cyclicity for postparturient cows, compared with findings for cows housed separately from bulls. Bull presence has also been shown to decrease the postparturient anestrus period of primiparous cows11,12 and to increase the number of primiparous cows cycling at the beginning of a designated postparturient breeding season.13 Additionally, results of another study2 revealed that estrus-detection bulls with intermittent or continuous access to cows identified a greater percentage of cows in estrus than did human observers who monitored herds for 30 minutes twice daily. Results of that study2 also indicated that bulls with continuous exposure were more successful at identifying cows in estrus than bulls with intermittent access to a herd.
Incapacitation of the CCP is a logical method to prevent achievement of erection. The CCP is a complex of vascular compartments interrupted by thin septae that arise from the crura of the penis proximally and envelop the corpus spongiosum and penile urethra distally to the level of the glans. The CCP is enveloped by the robust tunica albuginea, and expansion of the vascular volume of the CCP along with relaxation of the retractor penis muscles during sexual arousal results in erection and extension of the penis in the bull. The fibroelastic nature of the bovine penis allows for achievement of erection with relatively little increase in CCP volume, compared with species that have a musculocavernous type penis.14,15
Thrombosis of the CCP was reported as a cause of acquired impotence in a bull by Hudson16 in 1971. In a later case series, Ashdown et al17 described impotence in 9 bulls attributed to occlusion of the dorsal longitudinal canal of the CCP. That report17 provides a thorough discussion of the angioarchitecture of the cavernous structures of the bovine penis, including the bidirectional blood flow through longitudinal canals of the CCP that is requisite for erectile success.
Occlusion of the CCP was suggested3,4 as a method for preventing erection in, and intromission by, bulls used for estrus detection. This surgical technique aims to prevent expansion and engorgement of the CCP via blood flow from the crura of the penis during sexual stimulation. The procedure has been previously described3,4; however, follow-up information has been limited to anecdotal reports of success. In our hospital, CCP occlusion is achieved by means of a surgical approach to the penis and injection of an acrylic polymer into the CCP just proximal to the sigmoid flexure, causing an obstruction to blood flow. This procedure is believed to be well tolerated by bulls and a successful means of creating estrus-detection bulls. This technique is typically performed in conjunction with caudal epididymectomy to render the bull infertile as well as fixation of the distal bend of the sigmoid flexure to the fascia of the medial aspect of the gracilis muscle to prevent the passive extension of the fibroelastic penis that normally occurs through relaxation of the retractor penis muscles when the bull mounts a receptive cow.
The purpose of the study reported here was to retrospectively investigate surgical and long-term outcomes, including intraoperative and postoperative complications and use for estrus detection, of bulls that underwent CCP occlusion by means of acrylic polymer injection in addition to epididymectomy with or without penile fixation. Our hypothesis was that the procedure would result in low complication rates and produce bulls unable to achieve intromission while retaining appropriate libido for estrus detection purposes.
Materials and Methods
Case selection
Electronic and hard copy medical records from Purdue University Veterinary Teaching Hospital were searched to identify bulls that underwent CCP occlusion between January 1, 2002, and June 1, 2016. Keywords used to search the records database included “teaser,” “corpus cavernosum penis thrombosis,” “vasectomy,” and “epididymectomy.” Bulls were included in the study if they underwent the CCP occlusion procedure because they were intended for use as estrus-detection bulls and appropriate follow-up information was available. At a minimum, the following information was required to be present in the medical records for inclusion of a bull in the study: description of the surgical procedure and outcome, description of other procedures performed concurrently, signalment of the patient, and physical examination findings.
Long-term follow-up (> 6 months after the procedure) was performed by review of subsequent medical records when available or by telephone contact with the owner. All telephone follow-up was performed by 2 of the authors (AJD and ANB) using a questionnaire developed by the same authors for this purpose (Supplementary Appendix S1, available at: avmajournals.avma.org/doi/suppl/10.2460/javma.254.4.512). The follow-up questionnaire focused on success of the procedure, postoperative complications, success of the use of the bull for estrus detection with particular focus on the owner's assessment of the bull's libido and lack of ability to achieve erection or extension of the penis (and thereby intromission), and overall satisfaction with the procedure.
Medical records review
Data collected from the medical record included breed, age at time of the CCP occlusion procedure, and body condition score, estimated weight, or both. Details pertaining to the procedure, including restraint method, medications administered perioperatively, intraoperative or immediate postoperative complications, and any procedures performed in addition to the CCP occlusion, were also recorded. For study purposes, any difficulty resulting in a deviation from the intended routine procedure, such as contamination of the surgical site, failure of the restraint method, anatomic variation resulting in difficulty with surgical dissection and elevation of the penis, difficulty in handling or application of the acrylic polymer, or difficulty with the injection, was considered an intraoperative complication. Clinical complications included postoperative complications (surgical site abscessation, urogenital dysfunction [other than intended effects of the procedure], and incisional healing abnormalities), failure of the procedure to completely prevent penile protrusion, or premature loss of libido (preventing use of the bull for estrus detection for ≥ 1 complete breeding season).
Surgical procedure
The CCP occlusion was performed as previously described.3,4 Mepivicaine hydrochloride or 2% lidocaine hydrochloride solution (0.01 to 0.02 mL/kg [0.005 to 0.01 mL/lb]) was administered by caudal epidural injection. Bulls were restrained in a squeeze chute or placed in right lateral recumbency on a hydraulic tilt table, depending on patient tractability. The tail was restrained outside of the surgical field, hair was clipped from the buttocks and perineum, and the surgical site was prepared aseptically. A 10- to 15-cm vertical skin incision was made with a No. 10 scalpel blade attached to a No. 3 handle. The incision was created on the caudal midline, and approximately centered between the anus and base of the scrotum. Sharp dissection with the scalpel and Mayo scissors was used to continue through the subcutaneous tissue and thick fascia. Blunt digital dissection was used to identify, isolate, and elevate the penis to the incision, typically isolating the body of the penis just proximal to the sigmoid flexure. The urethral groove was identified by digital palpation, and the tunica albuginea of the CCP was penetrated just lateral to the groove with a 12-gauge hypodermic needle. The needle was advanced in a dorsoaxial plane until the tip of the needle made contact with the tunica albuginea at the dorsal aspect of the CCP (Figure 1). This contact was appreciated as a slight increase in resistance to advancement of the needle as well as by palpating a tenting of the tunica with the hand stabilizing the penis. Approximately 10 mL of sterile saline (0.9% NaCl) solution was injected to ensure proper placement of the needle within the CCP (adjacent to the urethra and corpus spongiosum penis). Placement was confirmed by ease of injection and palpation of flow within the penis. After confirming placement, the initial saline-containing syringe was detached and replaced with a syringe containing an acrylic polymer,a and up to 10 mL of the polymer was injected into the CCP until a palpable bulge was identified. The volume required varied, with bulls that had smaller penises usually requiring smaller volumes of acrylic. The typical injection volume was 5 to 10 mL. If the surgeon was unable to palpate filling of the CCP during acrylic injection, needle placement was adjusted and the injection was completed. If the bulge was identified and then became undetectable, a second injection was performed to ensure that the acrylic polymerized appropriately. At the surgeon's discretion, a penile fixation procedure was performed in some bulls by securing the tunica albuginea to the thick fascia of the medial aspect of the gracilis muscle at the level of the distal bend of the sigmoid flexure; this was accomplished by use of nonabsorbable sutureb in a single interrupted horizontal mattress pattern bilaterally. The skin incision was closed with nonabsorbable sutureb in a continuous pattern. If postoperative drainage was expected, the ventral portion of the incision was left open to heal by second intention.
Photographs of bull penises (necropsy specimens) depicting needle positioning for CCP occlusion by means of acrylic injection. A—A 12-gauge hypodermic needle was inserted into the CCP lateral to the urethral groove in a dorsoaxial plane just proximal to the sigmoid flexure (star). The paired retractor penis muscles are intact (arrow). B—Cross-sectional anatomy at approximately the level of the body of the penis. A 14-gauge hypodermic needle (selected for illustration purposes only) is placed to show the intended trajectory for correct placement of acrylic in the CCP. The tunica albuginea at the dorsal aspect of the penis (asterisk), CCP (caret), corpus spongiosum penis (black arrow), and penile urethra (white arrow) are shown.
Citation: Journal of the American Veterinary Medical Association 254, 4; 10.2460/javma.254.4.512
Following the CCP occlusion, a caudal epididymectomy was performed as previously described.4 The ventral aspect of scrotum was clipped of hair and aseptically prepared. If anesthesia of the area was not sufficient with the previously described epidural injection, the site was further desensitized by instilling 2 to 3 mL of mepivicaine or 2% lidocaine solution along the ventral aspect of the median raphe. The testicles were placed under tension in the scrotum by placement of a wide rubber tourniquet or an assistant's hand around the base of the scrotum. Two 2- to 3-cm incisions were made with the scalpel 1 cm abaxial to the median raphe to enter each scrotal hemisphere, and the tail of the epididymis was isolated, clamped, ligated, and transected, removing approximately 2 cm of epididymis. The scrotal skin incisions were closed with absorbable suturec in a single layer in the skin or left to heal by second intention at the surgeon's discretion.
Antimicrobials (oxytetracyclined [4 mg/kg {1.8 mg/lb}, SC, once], long-acting ceftiofure [6.6 mg/kg {3 mg/lb}, SC, once], or penicillin G procaine [22,000 U/kg {10,000 U/lb}, IM, once]) and an anti-inflammatory (flunixin meglumine [1.1 mg/kg {0.5 mg/lb}, IV, once]) were administered perioperatively on the basis of surgeon preference. Clients were instructed to prevent sexual stimulation of the bulls for 14 to 30 days and monitor animals for delayed return to normal behavior or signs of difficulty urinating. Routine postoperative care, including maintenance of bulls in clean, dry environments while incisions healed, and compliance with scheduled removal of skin sutures, was also recommended.
Results
Clinical details
Nineteen bulls underwent CCP occlusion during the study period, and follow-up information was available for 18. Long-term (> 6-month) follow-up was available from owners of 16 bulls, and 2 bulls had been treated at the hospital following the procedure. All bulls had the procedure performed as elective surgery, and none had substantial health abnormalities at the time of hospital admission. One bull was unilaterally cryptorchid. Most animals (7/18) were of mixed beef cattle breeds; there were also 3 Angus, 3 Shorthorn, 2 Herefords, 2 Simmental, and 1 Jersey. Ages (on the basis of owner-reported calving dates) ranged from 7 to 17 months (mean age, 11.1 months; median, 11.5 months) at the time of the procedure.
The CCP occlusion was performed with local anesthesia provided by epidurally administered lidocaine in 16 of 16 bulls that had information available in the record; the method of local anesthesia was not recorded for 2 bulls. The procedure was performed in a squeeze chute (15/18) or with the patient in right lateral recumbency on a hydraulic tilt table (2/18). The remaining patient was transitioned from standing restraint to right lateral recumbency during the procedure because it was unable or unwilling to remain standing. Procedures in the earlier years of the study period (prior to 2005; n = 5) were typically performed without perioperative antimicrobials or anti-inflammatory medications; however, more recent procedures (n = 13) typically included a single preoperative dose of flunixin meglumine (8). An antimicrobial was also administered for prophylaxis at the surgeon's discretion (ceftiofur crystalline free acid [6.6 mg/kg, SC] or penicillin G procaine [22,000 U/kg]; n = 3 and 8, respectively).
Although the penis was isolated and elevated and a test injection was performed in all cases, palpable filling with the acrylic was initially identified but then became unidentifiable in 2 bulls. Both animals had a second injection of the acrylic performed to ensure appropriate polymerization. Eight of the 18 bulls underwent penile fixation as well as CCP injection. The entire length of the perineal skin incision was closed in 15 patients; for the remaining 3, intraoperative contamination with feces resulted in the decision to leave the ventral portion of the incision open to facilitate drainage and heal by second intention. All 3 of these incisions healed without complication. All bulls had bilateral caudal epididymectomy performed, except that the bull with unilateral cryptorchidism was treated with unilateral caudal epididymectomy of the descended left testicle. The scrotal skin incisions were allowed to heal by second intention (16/18) or were sutured closed (2/18). The 2 bulls that had scrotal skin closure performed had excessive hemorrhage, and the scrotum was sutured to help provide hemostasis.
Outcomes
Complications pertaining to the acrylic injection occurred intraoperatively in 4 bulls; these included the 2 bulls in which failure to palpate the acrylic within the CCP necessitated a second injection, and an additional 2 in which the acrylic injection was noted as difficult, once because of leakage out of the tunica albuginea around the needle, and once because the acrylic polymer set prematurely within the syringe and needle. Subjective difficulty isolating the penis was noted in the records of 1 bull, and 2 had incomplete anesthesia of the surgical site requiring additional anesthetic administration. Three bulls had fecal contamination of the surgical site, including 2 with other complications (one was the bull transitioned to lateral recumbency when it would not remain standing, and the other had the described injection difficulty encountered owing to premature polymerization of the acrylic). In the 3 instances of intraoperative contamination, the surgical fields were copiously lavaged with sterile isotonic fluids, and the ventral aspect of the incisions were left unsutured to heal by second intention.
Two additional bulls were reevaluated at the study hospital because of postoperative complications. One of these bulls was examined because of vocalization and anuria 34 days after surgery. Clinical examination revealed ascites on abdominal ballottement; a rent in the urinary bladder was identified during exploratory laparotomy, and the bull was euthanized. Necropsy revealed occlusion of the penile urethra with acrylic in addition to the acrylic mass within the CCP and confirmed rupture of the urinary bladder. The remaining bull was evaluated 196 days after surgery because of swelling and fistulation of the perineum and was successfully treated for abscessation at the surgical site. Surgical debridement of the abscess removed an approximately 7 × 2-cm piece of acrylic that was adjacent to the penis. Electroejaculation following abscess lancing and lavage confirmed fixed retraction of the penis. This bull was discharged from the hospital with the intent that it would be returned to work for estrus detection but was lost to long- term follow-up. Neither of these 2 bulls had been noted to experience intraoperative complications. Both were excluded from the assessment of long-term outcome.
For the 16 bulls that did not have postoperative complications related to the CCP occlusion, the mean duration of follow-up was 58.25 months (median, 25.5 months; range, 6 to 172 months). Mean duration of use after surgery was 17.9 months (median, 13.5 months; range, 0 to 48 months). One bull developed severe orchitis related to the epididymectomy. This bull was owned and treated by the referring veterinarian and was culled without being used for estrus detection. Seven bulls were still in use at last follow-up. Of those still in use, the mean follow-up time was 15.9 months (median, 13 months; range, 11 to 26 months). Of the 9 bulls with long-term follow-up that were not in use, 4 were removed from the herd after 2 years of use as a matter of routine management, 2 were culled (one at 12 months and the other at 48 months after surgery) because of excessive bull-like behavior, and 1 was culled 6 months after the procedure owing to rectal prolapse of unknown cause, in addition to the 1 animal that had been culled because of orchitis. One additional bull was removed because of loss of libido 14 months after surgery.
Eleven clients owned the 16 bulls included in long-term follow-up. Seven of 11 clients reported continued use of the same bulls for estrus detection at the time of last follow-up. Nine clients gave a clear, yes-or-no assessment of whether or not they felt the use of these bulls was an effective method of estrus detection, and all responded favorably. When asked to rate each bull on a scale of 1 to 10 to assess overall satisfaction with the bull and procedure, mean response was 8.4 (median, 9; range, 1 to 10). A score of 1 (assigned for only 1 bull) was given for the bull that developed orchitis; for all other bulls, scores ranged from 6 to 10. Nine of 15 bulls that were used for estrus detection were reported to have maintained very good libido during use, with the remainder having libido described as good (n = 5) or okay (1). Owners of 12 of 16 bulls were confident in their ability to report whether the bull was able to protrude the penis. Ten bulls had no protrusion, and 1 (of 9 that did not undergo penile fixation) had partial protrusion. The remaining bull reportedly developed the ability to partially protrude the penis approximately 4 months after surgery, and the owner of this bull was unable to determine whether the protrusion allowed the bull to achieve intromission. Both bulls with partial protrusion were still in use for estrus detection at the time of follow-up (11 and 12 months after CCP occlusion was performed).
Although reported client satisfaction was generally high, some clients had discontinued the use of estrus-detection bulls altogether (n = 2 clients) or currently employed different procedures to modify bulls for this use (2). Reasons that clients provided for choosing other procedures included a lack of concern about venereal disease transfer because of closed-herd status; perceived decreased libido in bulls that had occlusion by acrylic injection, compared with those rendered infertile by other procedures; and various management changes. One client indicated that the use of estrus-detection bulls was discontinued when the breeding herd size was reduced, but that the same method would be pursued if the herd size was increased. The other client who no longer used estrus-detection bulls had implemented management changes to allow closer visual monitoring of the herd.
Discussion
Retrospective investigation of CCP occlusion by acrylic injection in 18 healthy, client-owned bulls < 18 months of age revealed that the procedure was well tolerated by the study population overall and successfully prevented full penile extension in all cases. Most (15/18) bulls were used for estrus detection purposes with satisfactory maintenance of libido (14) after the procedure. Clinical complications associated with the acrylic injection procedure were rare; these included abscess formation in response to the presence or leakage of the acrylic (n = 1), incorrect placement of the acrylic causing occlusion of the penile urethra and subsequent urinary bladder rupture (1), and failure of the procedure to accomplish the intended purpose of completely preventing protrusion of the penis (2). In addition, 1 bull developed orchitis related to the epididymectomy part of the procedure.
The bull that developed an abscess at the surgical site was treated 6.5 months after the initial procedure and a piece of acrylic, believed to be the nidus of infection, was removed from tissue adjacent to the penis. This bull was unable to extend the penis at the time of reexamination, presumably due to postoperative adhesions as a penile fixation procedure was not performed; however, partial occlusion of the CCP due to the inflammatory reaction induced by the presence of the acrylic could not be completely ruled out. The bull with dysuria had been reevaluated because of clinical signs 34 days after the surgery, and an acrylic cast occluding the urethra was confirmed on necropsy. We speculated that misplaced or leaked acrylic may have immediately caused partial occlusion of the urethra, with inflammation resulting from presence of the acrylic and altered urine flow eventually causing complete obstruction and urinary bladder rupture. Both of the bulls for which the procedure did not completely prevent penile protrusion were still being used for estrus detection at the time of follow-up; one of these had been marking cows and had no sign of protrusion of the penis until approximately 4 months after the procedure. This bull had undergone CCP occlusion, penopexy at the distal bend of the sigmoid flexure, and epididymectomy during the initial procedure, and it was not made available for reevaluation to attempt to elucidate the cause for this development. One possible cause for delayed failure of the procedure in this bull was possible incomplete occlusion of the CCP and eventual breakdown of the penopexy and postoperative adhesions during arousal, allowing partial extension of the penis. An additional consideration was that protrusion information was per owner observations, and no follow-up veterinary record was available; thus, it may have been possible that the owner could not differentiate between penile protrusion and passive prolapse of the prepuce.
As previously mentioned, the procedure used in the present study is intended to prevent engorgement of the CCP and resultant penile erection. As the initial protrusion of the penis during sexual stimulation includes passive relaxation of the retractor penis muscles and straightening of the sigmoid flexure, we typically augmented the CCP occlusion with fixation of the distal bend of the sigmoid flexure to the thick fascia of the medial aspect of the gracilis muscle to prevent passive extension. This method of penopexy differs from the traditional ventral midline fixation of the shaft of the penis, and we presumed it to be less secure. Although it has not been reported to our knowledge, there is a concern about suture failure should the bull develop engorgement. However, with successful prevention of CCP engorgement, this method of penopexy appeared to be reliable in bulls of the present study; however, it should be noted that whether protrusion developed was unknown in 4 of 18 bulls, and of 10 bulls that did not undergo penile fixation, 8 were reported to have no penile protrusion, suggesting that CCP occlusion and postoperative adhesions may be sufficient to prevent this passive protrusion.
In addition to the previously described incorrect anatomic placement of the acrylic, intraoperative complications recorded in the surgical records included subjective difficulty isolating the penis, difficult injection of the acrylic, incomplete anesthesia of the surgical site, and intraoperative gross contamination of the surgical field with manure. Difficulty with the dissection was anecdotally reported more frequently for heavier bulls with higher body condition scores, which was in agreement with a previous report2 indicating that candidates for estrus detection use should be identified at young ages and undergo surgery prior to reaching larger sizes. Furthermore, breed selection is an important consideration. We observed some producers using bulls of Jersey or other dairy breeds for estrus detection in beef herds. Advantages of such practice include ease of identification of the bull within the herd, and from a procedural standpoint, their typically lighter frames made surgical dissection and isolation of the penis subjectively easier. Ease of injection was variable. When difficulties arose, they were associated with the acrylic polymerizing prematurely and clogging the needle. The acrylic product used in these patients was chosen for its minimal exothermic reaction during hardening, although the working time when the product remains in liquid form is short (approx 1 to 2 minutes). On the basis of our surgical experience, the authors believe that the complication of incorrect anatomic placement of the acrylic can be prevented by carefully palpating the tenting of the dorsal aspect of the tunica albuginea (which occurs when the needle tip contacts this fibrous tissue) prior to injection and by assessing for the palpable bulge of the acrylic filling the CCP during injection. Furthermore, it is recommended to palpate the urethral groove with the hand stabilizing the penis for injection and to ensure that the needle enters the tunica albuginea laterally enough to avoid penetrating the urethra, as leakage of the acrylic into the urethra along the needle track is otherwise possible. The acrylic used was commercial grade and nonsterile; however, no adverse reaction to the acrylic was noted other than the 1 abscess that was presumed to be related to the acrylic leaking out of the tunica albuginea. Any inflammation associated with the acrylic was suspected to contribute to the occlusion by fibrosis and thrombosis of the CCP, but histologic analysis was not performed routinely in this population. Bulls that responded to surgical stimulation during the procedures received additional local anesthetic, were transitioned to right lateral recumbency, or both. In the authors’ opinion, some of these bulls were reactive to the surgeon's presence owing to poor tractability rather than persistent sensation.
In our hospital during the study period, we accomplished the CCP occlusion and related procedures in awake, physically restrained animals with appropriate local anesthetic administration, typically in standing patients. This is advantageous over other procedures used to prevent penile extension such as ventral midline penopexy and preputial translocation, because the number of assistants needed is reduced, compared with general anesthesia or restraint methods that include casting the patient or using a tilt table. As for any standing surgical procedure, the approach is suitable for a patient tractable enough for typical physical restraint methods and willing to stand for the duration of the procedure. Subsequent to the present study, CCP occlusion procedures in our hospital have been performed under light sedation according to a protocol previously reported for use in cattle18 in addition to caudal epidural anesthesia. Even with the implementation of a sedation protocol, the risks of feed withholding and refeeding associated with general anesthesia are obviated. Whereas preputial translocation is the procedure of choice for some practitioners,2 CCP occlusion as described herein is a less invasive and less costly procedure that can be done quickly.
Antimicrobial administration was allowed in these patients at the surgeons’ discretion. As there are currently no antimicrobial drugs labeled for perioperative prophylaxis in bulls, extralabel use of antimicrobial medications is the only option available for surgeons, and such use is restricted by federal regulations. Owners were informed of all recommended withdrawal times.
The CCP occlusion method used in the present study is relatively inexpensive, and considering the cost of keeping an estrus-detection bull for a year or more, some producers might elect to cull such bulls after the end of a breeding season and select another bull to undergo the procedure in the following year. Not only does such replacement minimize the cost of maintaining the bull (which can approximate $1,000 annually for yardage, pasture, and other feed),19 it provides other advantages to the producer. One of these advantages is avoiding the potential loss of libido over time as has been described for some estrus-detection bulls.20 This management scheme also allows for better control of the size and weight of such bulls, which might help prevent injury to heifers or cows during mounting. On the basis of our experience with the CCP occlusion procedure, we currently advise our clients to choose bulls intended for estrus detection early in life, which in our experience simplifies dissection and ease of monitoring after surgery. In our opinion, the ideal candidate for this procedure is a young (6- to 8-month-old) bull of a color different than the heifers and cows to be monitored. The difference in color is recommended to facilitate easy identification within the herd.
The present study had multiple limitations. The retrospective nature of the study resulted in some data missing from records, primarily related to patient details, examinations, and surgical procedures. Additionally, the follow-up period was long and our assessment of the long-term success of the procedure was reliant on client responses, which may have been affected by protracted intervals between surgery and use of the bull and the subsequent follow-up by telephone interview, as well as the owners’ subjective assessments. Additionally, histopathologic assessment of the CCP region affected by the injection of acrylic was unavailable in almost every case. However, on the basis of the follow-up information and self-reported owner satisfaction, we believe that CCP occlusion by acrylic injection accomplished the aforementioned goal of preventing CCP engorgement and, together with epididymectomy with or without penile fixation, produced bulls suitable for estrus detection in most cases, with 15 of 18 successfully used for this purpose. We could not confirm that the acrylic physically occluded the CCP; however, we speculate that presence of the acrylic may provide occlusion, serve as a nidus for thrombosis, incite inflammation and adhesion formation, or result in a combination of these factors. The authors view simple fixation of the sigmoid flexure to the fascia of the gracilis muscle as an augmentative prevention method that can be performed quickly at the time of the other surgical procedures. However, the CCP occlusion alone appeared to be sufficient to prevent protrusion of the penis in many of the bulls of this study and was generally well tolerated.
Acknowledgments
No funding or financial support was received by the authors in connection with this retrospective study. The authors have no financial or ethical conflicts of interest to disclose.
ABBREVIATIONS
| CCP | Corpus cavernosum penis |
Footnotes
Justi-hoof acrylic. Justi Products, Oxnard, Calif.
No. 1 Supramid Extra, S. Jackson Inc, Alexandria, Va.
2–0 Monocryl, Ethicon US, West Somerville, NJ.
Liquamycin LA-200. Zoetis Services, Parsippany, NJ.
Excede (ceftiofur crystalline free acid) sterile suspension. Zoetis Services, Parsippany, NJ.
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