Stallion Subfertility and Infertility Conditions

Is your stud a dud? About one in 10 breeding stallions can’t perform up to expectations due to subfertility or infertility. Causes for reduced breeding performance are many: Age, injury, genetics, management, or disease.
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Is your stud a dud? About one in 10 breeding stallions can’t perform up to expectations due to subfertility or infertility. Causes for reduced breeding performance are many: Age, injury, genetics, management, or disease. Two are readily identifiable, but not completely understood, conditions–urospermia and hemospermia, respectively meaning urine in the semen and blood in the semen.


How troublesome is hemospermia? The actual presence of blood in the ejaculate poses little risk to the mare and seldom bothers the stallion, but it could be one big headache for the stallion owner.

“You can lose an entire breeding season due to hemospermia,” says Claire Card, DVM, PhD (physiology), Dipl. ACT, professor at the Western College of Veterinary Medicine, Large Animal Clinical Sciences, Saskatoon, Canada. “Sperm and blood do not mix well at all in terms of preserving fertility of the sperm. Fortunately, it’s fairly straightforward: We don’t generally see an extension of the problem internally into a bladder or kidney problem. It remains localized to the urethra.”

Causes The underlying cause of hemospermia often remains unidentified. Large or small amounts of blood can enter the semen due to several reasons:

  • Trauma to the urethra or penis (such as breeding mares through a fence, falling while breeding and excessively bending the penis, attempting to jump over a fence with a full erection and causing injury, etc.);
  • Infection or inflammation of the urethra or accessory sex glands;
  • Cutaneous habronemiasis (a disease caused by parasites in the urethral process);
  • Squamous cell carcinoma of the urethral process;
  • Neoplasia of the bladder;
  • Bladder stones passing through the urethra.

“But in most cases, we don’t really understand why the condition develops,” says Card.

Although it occurs in all breeds, in Card’s practice idiopathic hemospermia (cases with no known cause) seems to appear in Quarter Horse purebreds and crosses with higher frequency.

Clinical Signs Often, owners are unaware their stallions have this condition until after a natural breeding. “People usually first notice it after a stallion covers a mare, and he comes out covered with blood,” Card explains. “The mare is often covered with blood as well.”

Sometimes the problem is less evident, with the stallion dripping just a little blood from the penis before or after breeding.

In cases where the horse is collected for insemination, semen shipment, or cryopreservation, the owner or veterinarian might notice a slight to obvious color change of the semen to a red or brown tint, says Sara K. Lyle, DVM, Dipl. ACT, clinical instructor, Veterinary Clinical Sciences, Louisiana State University School of Veterinary Medicine.

“Some cases of microscopic hemospermia are not noticed until the ejaculate is allowed to settle (e.g., with fresh-cooled shipment) or is centrifuged for processing (cryopreservation or fresh-cooled shipment),” Lyle explains.

In the absence of obvious clinical signs, some owners first discover something is amiss when pregnancy rates diminish.

Diagnosis Determining a diagnosis begins with a full physical exam followed by an examination during sexual arousal. Card explains, “The stallion is brought to the breeding shed, the mare is teased, and he’s evaluated when he has a full erection and is highly aroused.”

The veterinarian checks external tissues such as the urethra and penis for soreness or bleeding. “Blood could come from a pinpoint injury on the end called the glans penis, in which case the horse would be asymptomatic until he was fully aroused,” Card says. “When his penis becomes engorged and erect, blood would spurt out the end of the penis at the site of injury due to the build up of pressure; but this does not occur unless his penis is erect. If there is no evidence of a problem during the external examination of the penis, the stallion is collected and the semen evaluated for blood.”

To assess the severity, the nature of the disease process, and the location of the problem, the horse is collected or sexually aroused, sedated, then undergoes a urethral exam.

“Most lesions are characteristically found where the urethra takes a bend as it exits the pelvis and enters the penis,” Card says. “Using the endoscope, we can evaluate whether it’s a crater-like ulcer, raised granulomatous lesion, if there’s a fresh rent (tear, suggesting trauma) in the urethra, or infection. Once identified, we culture the urethra or the ulcer itself to see if there is a bacterial component to the problem. Ulcerated lesions, in our experience, are often associated with secondary bacterial infection, but some of the granulomatous lesions or the simple traumatic ones may or may not be associated with infection.”

Treatment If the source of the lesion and infection are identified, culture results and sensitivity from the examination of the bacteria determine which antibiotics can best address the problem, Card says. Otherwise, antibiotics are sometimes prescribed empirically. Sexual rest is probably the most important component for recovery.

“Sexual arousal keeps the ulcers or sores open and active,” warns Card. “Every time the horse becomes sexually aroused, the internal pressure mounts within the penis and urethra, leading to bleeding, which prevents the lesion from healing. We suggest absolute sexual rest, not just from breeding, but also from contact with mares where the stallion might become sexually aroused, for a minimum of three weeks. After three weeks, the horse is reevaluated for the presence of blood at sexual arousal or blood during ejaculation. Some horses are able to return to breeding at that point, but most take longer. Then, we’re usually dealing with a three-month period of rest.”

Fortunately, most horses respond to antibiotics and rest. However, Lyle notes that the risk of reoccurrence is increased, so monitoring is advised.


Like hemospermia, urospermia doesn’t present health risks for the stallion, but it can result in variable degrees of infertility. “The amount of urine contamination usually varies from ejaculate to ejaculate, therefore, the damaging effects on the fertilizing capability of the sperm cells is variable,” Lyle reports. In addition, urospermia can cause temporary endometritis in the mare.

Causes “Urospermia has been hypothesized to occur from a dysfunction of the normal neural pathways controlling the tone of the bladder neck sphincter during ejaculation,” says Lyle. “Stallions with bladder paralysis (cauda equina syndrome secondary to equine herpesvirus-1 infection or sorghum-sudan grass toxicity, among others) may also have urinary incontinence during ejaculation. Some cases are caused by nerve damage (e.g., equine herpesvirus-1 infection).”

Clinical Signs The onset of urospermia is seldom apparent to owners. “If the mating system used is natural cover, the first sign the owner might be aware of is a reduction in the per cycle conception rate or overall pregnancy rate,” Lyle says. “If the horse is collected for insemination, semen shipment, or cryopreservation, then the first signal may vary from a reduction in motility (if the amount of urine contamination is minute and the urine is dilute) to an obvious color change to a yellow tint. But it is unlikely that any overt clinical signs will accompany the onset of urospermia. Stallions with overt bladder paralysis may dribble urine between periods of sexual activity; however, it would be more common that urospermia began prior to the recognition of obvious urinary incontinence.”

Diagnosis This is based on semen analysis, specifically abnormal amounts of urea nitrogen, creatinine, or blood urea nitrogen (BUN), and alterations in pH and osmolarity (ability to pass through a membrane), says Lyle. “Usually, the osmolarity of semen contaminated with urine will be greater than that of noncontaminated semen. Changes in osmolarity and pH are detrimental to spermatozoal motility.

“Because urospermia can be caused by nerve damage, a complete neurological examination is also advised,” says Lyle.

Treatment Medical and nonmedical management is geared toward reducing the detrimental effects of urine on the sperm cells and minimizing contact of urine with the spermatozoa. “Treatment is typically on a trial basis, which makes determining response to therapy difficult to evaluate,” Lyle says. She offers the following recommendations:

  • Training to urinate prior to collection, either by voice command or by exposure to another stallion’s fecal pile;
  • Catheterization of the bladder to evacuate urine prior to collection;
  • Fractionation of ejaculates with an open-ended artificial vagina (for breeds allowing artificial insemination). “The semen is separated into fractions during collection with an open-ended artificial vagina by diverting the jets of the ejaculate into a series of receptacles,” explains Lyle. “By doing so, we can determine when urination is occurring during ejaculation. The creatinine or urea nitrogen of each fraction is measured to determine which one is contaminated with urine. If a pattern can be discerned and is consistent–i.e., he consistently urinates into the same fraction during subsequent ejaculations–then fractionation can be a useful tool to prevent contamination of the semen with urine;”
  • Dilution with milk-based extenders, sometimes followed by centrifugation to remove the supernatant (the soluble liquid fraction of a sample following centrifugation) containing the urine (although a controlled study showed centrifugation provided no additional benefit over dilution with the semen extender);
  • Infusion of semen extender into the mare’s uterus prior to natural mating to reduce the degree of contamination with urine or to minimize the detrimental effects of urine on spermatozoal function.

Additionally, drug therapy could help by increasing the tone of the bladder neck or decreasing the tone of the detrusor muscle (a muscle of the bladder wall that helps expel urine), says Lyle, although efficacy is uncertain. “Medical management is variably successful, largely because the exact dysfunction is rarely known.” Drugs used to address this condition include:

  • Flavoxate hydrochloride (relaxes the bladder wall);
  • Bethanechol chloride (improves coordination of the sphincter and detrusor function);
  • Imipramine (an antidepressant with properties used to treat stress and urge incontinence in people and cats and ejaculatory dysfunction in stallions).

Prognosis A complete resolution of urospermia is difficult. For most affected stallions, management can reduce the detrimental effect on the sperm cells and make pregnancies possible; the likelihood of this varies with the stallion, ranging from good to guarded.

“While a horse may have less contamination in an ejaculate on a given day, he should be considered always at risk for urination during ejaculation,” explains Lyle. “Therefore, monitoring and management generally become a permanent recommendation for the remainder of his breeding career.”


The causes of urospermia aren’t completely identified, so recommendations for preventive techniques are lacking.

About the only thing an owner can do to reduce the risk of trauma-caused hemospermia is to employ sound management techniques, including good fences to prevent horses from getting out and keep them from breeding through the fence.


Written by:

Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She’s schooled in hunt seat, dressage, and Western pleasure.

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