Overview of Selected Pathologic Conditions in Breeding Stallions: Hemospermia, Poor Semen Quality, Enlarged Scrotum

1. Introduction

Equine veterinarians can be faced with challenging cases that are outside the scope of their usual clinical paradigm. Issues with breeding stallions oftentimes fall into this category, as breeding stallions are not a common patient for many practicing veterinarians. This paper addresses three reproductive conditions of stallions that may require veterinary intervention. The accompanying interactive presentation will highlight aspects of these topics through discussion of bona fide cases.

2. Hemospermia

Hemospermia refers to the presence of blood in semen. The amount of blood in the semen can vary from minute to large, with the amount of blood giving some indication of the cause of the hemospermia. Blood-laden ejaculates are generally detected easily by their pink to reddish to frank red color. Less obvious contamination is detected by microscopic analysis. A disproportionately elevated ratio of neutrophils to erythrocytes in semen or a brown or reddish brown semen color (often indicating presence of non-fresh blood) is suggestive of an internal genital infection, such as that associated with seminal vesiculitis, epididymitis, or orchitis.

Stallions with overt blood in ejaculates have been reported to be highly subfertile to infertile^1,2; however, this is not always the case. For one Thoroughbred stallion breeding by natural cover, per-cycle pregnancy rate was 67% (97/144) for covers with no blood in dismount semen and 64% (29/45) for covers in which the dismount semen contained blood. The following year, per-cycle pregnancy rates were 70% (78/1111), 78% (21/27), 65% (17/26), and 50% (4/8) when dismount semen contained no blood, slight blood, moderate blood, or extensive blood, respectively (D. Varner, personal observations). This demonstrates that a certain amount of blood contamination of stallion ejaculates is compatible with good fertility. Laboratory studies on the effect of whole blood on in vitro fertilizing capacity of bull semen revealed that the presence of added blood had a negative effect as amounts of added blood increased from 0 to 1.5%.³

The effect of hemospermia on equine sperm quality or fertility following cooled storage has not been critically studied. When blood-contaminated semen of one stallion was mixed with an extender prior to artificial insemination, a high pregnancy rate was achieved.⁴ Pregnancy rate was also not hindered for one stallion with frank blood in semen when extender was placed in receptacle of artificial vagina prior to semen collection (T. Blanchard, personal communication, 2015).

There are many causes of hemospermia, but the condition is generally related to lacerations/abrasions on the exterior penis or urethral process, urethral defects (rents), or infection/inflammation of the prepuce, penis, urethra, accessory genital glands, epididymides, or testes. Tumors of the penis (e.g., squamous cell carcinomas [SCC] or, uncommonly, papillomas) and active penile lesions associated with equine coital exanthema may also result in hemospermia.⁵

Penile SCCs are identified more frequently in geldings than stallions.^6,7 This is likely due, in large part, to the fact that most male horses are castrated; and that geldings may accumulate more smegma in the prepuce than actively breeding stallions. Smegma has been found to have carcinogenic properties.^8,9 Although the glans penis, penile body, and prepuce are the most common sites for male genital SCC, primary SCC involvement of the urethral process resulting in hemospermia has been reported.¹⁰ There has been a flurry of research in recent years on the pathogenesis and relationship between equine penile papillomas, in situcarcinomas, and invasive SCC.^11,12 The gross appearance of penile and preputial surfaces with these lesions vary from smooth raised hyperplasic plaques to wart-like growths to irregular masses with ulceration and secondary bacterial infection. Using molecular techniques, the equine papilloma virus, EcPV2, has been found in all three lesions. (Two other equine papilloma viruses are associated with classical equine papillomas, EcPV1 and equine aural papillomas, EcPV3).

Although bacterial urethritis in the region of the ejaculatory ducts has been described as a common etiology for hemospermia,¹ this cause may have been misdiagnosed. Habronema-induced granulomas of the urethral process (cutaneous habronemiasis) were once a relatively common cause of hemospermia, but their prevalence has reduced considerably in the past three decades, probably owing to the widespread use of ivermectin and, more recently, moxidectin, as parasiticides.

The most common cause of profuse contamination of semen with blood is an idiopathic urethral defect (or rent) that communicates with the surrounding corpus spongiosum penis.^13,14 The defect is generally associated with hematuria in geldings, but the presenting complaint is generally profound hemospermia in stallions. Bleeding is profuse because the lesion communicates with the underlying corpus spongiosum penis. As such, bleeding typically occurs at full erection, when the glans penis and communicating corpus spongiosum penis (which surrounds the urethra) are fully engorged. Mean peak pressure in the corpus spongiosum penis at the time of coital ejaculation in a pony stallion is reported to be 762 mm Hg, compared with 17 mm Hg during the quiescent state.¹⁵ The lesion(s) is (are) typically small (2–5 mm in length) and is (are) are almost always located on the posterior surface of the urethra near the pelvic ischium.

Diagnosis of hemospermia begins with an assessment of the quantity of blood in the semen given that minute amounts of blood are oftentimes associated with abrasions or small lacerations on the surface of the penis. The penis should be visually inspected and palpated, paying particular attention to the distal end of the penis, including the urethral process and the fossa glandis. Lesions within the dorsal urethral sinus or the ventrolateral sinuses can be difficult to detect. Within the fossa glandis, the dorsal urethral sinus seems to be particularly susceptible to SCC or to epidermal hyperplasia with associated submucosal neovascularization, lymphoplasmacytic inflammation, mucosal ulceration, and associated hemorrhage at the time of ejaculation.

To aid visualization of the fossa glandis, the penis can be firmly grasped at the time of stallion dismount from a mare or breeding dummy immediately following ejaculation to maintain distension of the glans penis. This will allow easier visual and digital examinations of the fossa glandis. The area can also be balloted with a paper towel to remove any standing blood so that the origin of any bleeding can be more easily recognized. Maintaining engorgement of the penis with digital pressure following ejaculation will also allow for better inspection of the surface of the glans penis for bleeding lesions.

If profound hemospermia is detected and of urethral origin, then a urethral defect is a likely cause and should be included at the top of the list of differential diagnoses. If the blood contains a disproportionately large number of neutrophils, then seminal vesiculitis is a likely cause. Diagnosis of either of these conditions is best achieved using urethral endoscopy. The method for performing this examination was reported previously.¹⁶

Treatment of the hemospermia is dependent on the underlying diagnosis. Surface lesions on the penile shaft can often be treated with locally applied emollient and sexual rest. Lesions that penetrate into underlying cavernous spaces, such as those occurring with use of wire brushes to curb masturbation, may require surgical closure. Lesions within the fossa glandis can be difficult to treat. [...]