CHAPTER 167 Diseases of the External Genitalia of Stallions
Stallion infertility may be associated with seminal abnormalities, behavioral and mating disorders, venereal diseases, and abnormalities of the genitalia. Conditions affecting the external genitalia are usually traumatic but may also include infections and neoplastic conditions.
Traumatic injuries to the penis and prepuce may be caused by a kick from a mare during mating, the result of improperly fitted stallion “rings,” and from vulval “breeding stitches.” Most traumatic injuries to the external genitalia that occur during breeding occur at the time the stallion attempts to mount or during the dismount phase of mating. Adequate restraint of the mare during mating is essential. A twitch should be applied to the upper lip, and if the mare starts to kick, the mare handler should pull the mare’s head toward the stallion so that the mare’s buttocks move away from the stallion. Padded felt boots can be fitted to the hind feet of mares to ameliorate the effects of a kick, if one occurs. However, many mares object to the boots being put on their hind feet. Elevating a forelimb may also be used as an additional safety mechanism for the mare and stallion. Individual mares may require tranquilization. The interval from administration of a tranquilizing agent to onset of adequate tranquilization varies with the medication being used and route of administration. Xylazine and butorphanol tartrate result in sedation in 5 to 10 minutes, whereas acepromazine usually requires an interval of 20 minutes to induce tranquilization. If a mare is reluctant to be mated by the stallion, involved personnel need to ensure that the mare is in estrus and the time for mating is optimal. Obviously, traumatic injury may occur during hand mating or pasture breeding. Kicks usually result in injury to the forelimbs and chest, stifle joint area, prepuce, and very infrequently to the penis or gonads directly.
When artificial insemination is used, lacerations to the erect penis may be caused by improperly fitted, cracked, or wrinkled phantom covers. When artificial vagina liners are secured by rubber bands, the bands may occasionally slip onto the penis during thrusting. If the band is quickly stripped off the penis, a seroma may result. Instead the penis should be gripped proximal to the band and the band then cut or lifted off the penis.
Stallion paddocks should be separated from mare paddocks by double fencing, at least 10 feet apart, or the stallion may attempt to mate across the fence, resulting in lacerations and trauma to the external genitalia.
Extreme care must be exercised when catheterizing the stallion’s urethra because of the risk of causing urethral irritation and bacterial contamination. The fossa glandis is a common source of both potentially pathogenic and nonpathogenic bacteria. The end of the penis and urethra should be thoroughly cleansed before catheterization is attempted, using sterile gloves and a sterile catheter. Repeated catheterization of the same stallion should be kept to a minimum.
Trauma to the penis and prepuce may result in edema or hemorrhage. Preputial edema may be localized or quite extensive as a result of the loose and elastic skin tissue of the prepuce. The penis may prolapse from the preputial sheath, often bowing in a caudal direction. Once the penis has prolapsed from the prepuce, dependent edema of the penis will occur. The penis and prepuce should be elevated and supported to aid fluid return from the damaged tissues. This can be achieved using a stallion supporting device or an encircling abdominal bandage that should include the penis and prepuce. If only the penis is damaged, the penis can be supported in the prepuce with temporary retention sutures, which close the preputial orifice. The penis must be periodically withdrawn for cleansing. Emollient creams are topically applied to the penis to prevent the penile skin from drying and cracking. Pressure bandaging and penile massage may prevent further penile swelling and reduce existing edema. When paraphimosis occurs, exercise must be limited to avoid further damage to the prolapsed penis. Cold-water hydrotherapy and massage (30 minutes per treatment, two to four times daily) may prevent further fluid accumulation. After the threat of further edema or hemorrhage has passed, warm-water hydrotherapy may help to disperse fluid from the affected tissues.
Antimicrobial ointments should be applied if there are penile or preputial lacerations or abrasions. Systemic antimicrobial treatment is recommended for deeper lacerations. Phenylbutazone, aspirin, and flunixin meglumine are helpful as anti-inflammatory agents and analgesics. Treatment may be necessary for as short a period as 2 to 3 days or as long as 2 to 3 months.
Tranquilizers are contraindicated in horses with paraphimosis or penile injury because they cause further penile prolapse and edema formation. Sexual arousal should be avoided in the early stages of penile injury because attempts at erection will increase penile blood pressure, which may cause further hemorrhage or edema. If swelling and edema are limited to the prepuce, penile erection may aid massage therapy, hydrotherapy, and application of emollients or antimicrobial salves.
Paraphimosis may also occur as a secondary phenomenon in equine infectious anemia, purpura hemorrhagica, rhinopneumonitis, exhaustion, starvation, and penile paralysis. The prolapsed penis should be supported and moistened with ointments to prevent traumatic injury.
Ultrasonography of the external genitalia may be useful in determining the source of hemorrhage or edema, particularly if the penis itself is involved. Fluid accumulation within the scrotum should also be assessed, as spermatogenesis will likely be affected for as long as 2 to 4 months. Edema and swelling of the scrotum and its contents result in inflammation and an insulation effect on the testicular thermoregulatory mechanism, resulting in disrupted spermatogenesis.