Stud exams preserve fertility


Much of the focus and effort put forth on breeding farms this spring will center on mares and the various reproductive problems that they experience. Stallions are often given minimal attention other than bacterial cultures and examination of early season ejaculates unless there are unusually high numbers of return "open" mares or evidence of serious problems.

Much of the focus and effort put forth on breeding farms this spring will center on mares and the various reproductive problems that they experience. Stallions are often given minimal attention other than bacterial cultures and examination of early season ejaculates unless there are unusually high numbers of return "open" mares or evidence of serious problems.

But it takes two to tango, and stallions also are affected by any number of conditions that can impact their ability to mount, ejaculate or "settle" mares. A look at the most common causes of lesions of the penis and testicles of the stallion may alert practitioners to potential problems that can be addressed at an early stage and possibly deal with aggressively. This knowledge and early management can save potential fertility in some stallions and might help make this season a successful one.

Relatively early stages of penile squamous cell carcinoma will show up as red to whitish raised areas on the penis and prepuce. Lesions of this type and stage might cause little to no clinical problems with either collection or natural service but the sooner these areas are noticed and biopsied, the sooner treatment can be started.

Paraphimosis, or swelling of the penis, is one of the most commonly seen problems in breeding stallions.

"Breeding injuries and trauma from phantom (artificial collection mounts) accidents cause the majority of stallion injuries that we see," says Dr. Charles Love, a member of the Department of Reproduction at the College of Veterinary Medicine at Texas A&M University.

Aggressive Thoroughbred stallions often charge mares, and aggressive mares occasionally kick stallions. Either of these scenarios can result in blunt-force trauma to the penis of the stallion, "essentially a smashed penis", Love says. "Breeding managers have become so comfortable collecting stallions off a phantom that they tend to think that all of the potential risk has been removed. Yet charging the phantom or misalignment, especially with an aggressive breeder, can result in significant trauma, penile hematoma and paraphimosis."

Dr. William Ley, an equine reproductive specialist in private practice in Virginia, concurs that a kick from a mare before, during or after breeding is the most common cause of injury to the stallion and can result in scrotal contusion, testicular hematoma or penile paraphimosis. These stallions usually will present with a slight elevation in temperature due to a pain response and with very obvious swelling of the affected area. Ultrasound examination will confirm the presence of edema. If an acute testicular hematoma is present, it might be hypo-echoic or anechoic (areas of reduced or absent ultrasound signal that appear as black spaces) due to an accumulation of blood within the tissue. Chronic lesions will appear hyper-echoic (areas of whiter ultrasound shading) due to fibrosis. Prognosis for these types of injuries is guarded, but quick recognition of the problem and aggressive treatment may preserve acceptable stallion performance and fertility.

Trauma care

Treatment for traumatic swelling or paraphimosis requires aggressive measures to reduce edema. Love recommends vigorous massage of the penis and periodic cold hydrotherapy during the initial 24-hour period.

"And I do mean massage as often as possible over that initial period requiring that the stallion be in a location offering 24-hour care," he says.

The goal is to be able to retract the penis into the prepuce, which then greatly increases the chances of a successful outcome. Anti-inflammatory medications, such as flunixin and dexamethasone, can be used along with topical antibiotics to reduce the chances of infection. Salix and Naquasone (trichlormethiazide and dexamethasone combination) also can be used to reduce edema, but there is no substitute for hydrotherapy and massage. Caution must be used, though, with the application of cold water because reduced blood flow to the penis can result in tissue trauma if the cold is excessive or used continuously for too long. Short (eight to 10 minute) applications every hour are best. The use of compression bandages or various slings designed to help hold the penis up against the ventral abdomen can be very beneficial as it helps offset gravity and allow easier reduction of edema. Still, the primary goal is to replace the penis within the prepuce as quickly following trauma as possible.

There are other, less common conditions that can cause paraphimosis in the stallion. Certain drugs, such as acepromazine tranquilizer and other phenyl-thiazine agents, will cause potentially devastating paraphimosis and should never be used on stallions. Liver disease can occasionally cause penile swelling, and weakened, debilitated stallions may also suffer this complication.

Oncologic developments

Tumors of the equine penis are not that common but are seen often enough to be important. Additionally, as advances in equine science allow horses to live longer and advances in reproductive areas make these older horses capable of breeding at later stages of their lives, veterinarians will be seeing an increase in the presenting cases of equine cancer.

Seminoma of the equine testicle is usually a benign neoplasia in the horse and the most common testicular cancer seen. Benign teratomas are tumors of pluripotential germ cells seen infrequently and usually in retained testicles. Sertoli cell and Leydig cell tumors are also seen but are really quite rare. Melanomas of the penis and/or prepuce are also seen, as are sarcoids, but the most common penile tumor in horses is squamous cell carcinoma (SCC; See photo). This is a locally aggressive metastatic cancer that requires early diagnosis and usually aggressive treatment for a successful outcome. Squamous cell carcinoma is thought to derive from either the epidermis or the epithelium of the outer root sheaths of hair follicles, which is paradoxical because this tumor tends to occur most frequently in non-haired, non-pigmented areas. Clinically, SCC appears as red to whitish raised plaques that rapidly take on an irritated appearance and grow to resemble granulation tissue in later stages. Often breeding managers are alerted to the presence of these lesions during routine cleaning of stallions prior to breeding/collection or by the presence of blood on the penile shaft following breeding/collection. Abrasion of these lesions during reproductive use causes bleeding and in advanced stages, the stallion might be unwilling to mount and/or breed.

Biopsy of these lesions is necessary to make the diagnosis. If the lesion is solitary and in an accessible area, then surgical excision is recommended. Though SCC of the tip or head of the penis is the easiest for the equine surgeon to approach, Love urges caution with excision in this area.

"Be careful about losing elasticity in this area as the penile head tends to rip or tear constantly on ejaculation following some surgical excisions," he says. "Surgical repair or removal of lesions near the tip of the penis is often less rewarding on breeding stallions."

Various topical anti-cancer creams and preparations, such as 5-fluorouracil (5-FU) have been advocated for SCC treatment by various clinicians, and the general opinion is that this treatment approach works best if used early and often when lesions first appear. Use of these topicals typically will cause swelling of the penis and some local irritation, so breeding is not possible during this period.

"Veterinarians should be concerned with 5-FU and other anti-cancer drugs, especially with long-term administration because these agents affect rapidly dividing cells (cancer cells and sperm cells) and they may affect fertility," Love says.

Surgical laser ablation is becoming more commonly used on SCC of the penis, especially if the lesion is widespread and extensive. Diode or CO2 lasers are most frequently used and the procedure is done under general anesthesia.


Coital exanthema is another problem seen in both mares and stallions. This condition is a benign venereal disease that probably occurs worldwide and is caused by equine herpes virus type 3 (EHV-3). Stallions with EHV-3 generally exhibit multiple circular red nodules up to 2 mm in diameter seen on the penis or prepuce. Intromission is painful with these lesions and the stallion may be reluctant to collect or breed naturally. Though coital exanthema can be confused with other penile lesions and can affect a stallion's performance, it has no effect on fertility. Sexual rest for a period of about three weeks, isolation from other horses and antibiotic cream applied topically to prevent secondary infection is usually curative.

Bacterial infections of the penis and testicles are infrequently seen but have been reported. Pseudomonas, Klebsiella, Streptococcus equi, Salmonella and E. coli are the bacterium most commonly involved in these cases. Contagious Equine Metritis (CEM) is usually seen in mares but can be found in stallions and equine viral arteritis (EVA) can also cause infection and testicular swelling.

Testicular torsion is another problem that can be seen in breeding stallions. Torsion is usually of 180 or 360 degrees and can be either acute or chronic. Acute torsion is the form most common to practitioners and associated with abdominal pain and colic. Careful palpation of the testicles usually reveals a hot, tender 180-degree rotation or, in more advanced stages, a cold testicle. Surgical removal of the affected testicle is usually necessary, but these stallions may continue to breed successfully to a reduced book of mares. Chronic torsion can be more difficult to diagnose and is sometimes overlooked. These stallions may twist intermittently without clinical signs or with only mild discomfort and reluctance to ejaculate. There may be some hind limb swelling or scrotal swelling, but these torsions can be difficult to palpate, and practitioners should remember to consider this problem based on a continuing history of intermittent breeding difficulty.

The breeding stallion is half of the reproductive pair, and attention to the potential problems and diseases seen in these animals is easily as important as all the time spent palpating, culturing and flushing mares. Though stallion issues do not come up with the same frequency as do those in mares, serious conditions can occur, and early recognition and treatment might help save a stallion's fertility and may help save your client's breeding season.

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