Overview of Seminal Vesiculitis in Bulls
The seminal vesicles are paired accessory sex glands located on the floor of the pelvis, lateral to the ampullae, and dorsal to the neck of the urinary bladder. The vesicles secrete a clear fluid that adds volume, nutrients, and buffers to semen. The term “seminal” vesicle is a misnomer, because the vesicles are not a reservoir for spermatozoa.
Seminal vesiculitis is an inflammation and often an infection of one or both vesicular glands. The purulent material associated with vesiculitis is a contaminant of semen and is a cause for semen to be discarded from bulls collected at an artificial insemination center. Bulls found to have vesiculitis during a breeding soundness examination are considered unsatisfactory breeders. Bulls refractory to treatment efforts should be culled.
Vesiculitis has been reported in bulls wherever breeding cattle are raised. The reported incidence of vesiculitis in the general population of bulls is 1%–10%. However, incidences of 20% and even 49% have been reported for bulls housed in groups. Bulls of all ages can be affected, but vesiculitis is most frequently seen in yearling bulls presented for a breeding soundness examination or collected for the first time. Because many yearling bulls affected with vesiculitis are culled, it is seen less frequently in adult bulls.
Vesiculitis is typically considered to be caused by bacterial infection. The most commonly identified bacteria are Trueperella pyogenes, Pseudomonas aeruginosa, streptococci, staphylococci, Proteus spp, and Escherichia coli. Other microbial agents implicated include Mycoplasma bovigenitalium, Chlamydia spp, and viruses.
Postulated pathogenic mechanisms include infectious agents ascending the urethra to the vesicle, descending through the ductus deferens from the testicles or epididymides, or metastasis from another tissue or organ hematogenously. The ascending route of infection is considered unlikely unless the bull has accompanying penile trauma or urethritis. The descending route would be considered if the vesiculitis is ipsilateral to an infectious epididymitis or orchitis. Vesiculitis subsequent to systemic infection, umbilical infection, infectious arthritis, or pneumonia is considered more plausible.
Congenital malformation of the excretory ducts of the vesicles where they open into the urethra at the colliculus seminalis has been reported. A malformation of the excretory duct orifice permits reflux of spermatozoa or urine from the pelvic urethra into the vesicle. If the tubular lining of the vesicle degenerates subsequent to irritation from abnormal material in the ducts, significant local inflammation can result. This noninfectious etiology may account for the poor therapeutic response in some cases.
Vesiculitis is usually first suspected after collection of a semen sample grossly contaminated with purulent material. If the bull has vesiculitis, the rectal examination typically reveals an enlarged, sometimes irregular, and often fibrotic vesicle. Vesiculitis may be unilateral or bilateral. If vesiculitis is unilateral, there is usually asymmetry in the size of the glands. Infrequently, a vesicle will be abscessed; in such cases, the affected vesicle is markedly larger than the other and may be fluctuant on palpation.
Purulent contamination of semen is not pathognomonic for vesiculitis. A bull with epididymitis, orchitis, or posthitis may also have semen contaminated with purulent exudate. The entire genital tract must be examined to determine a possible cause for the abnormal semen. The prepuce may need to be douched with water or saline before collection of semen to exclude posthitis as a transient cause of pus in semen. Semen may be cultured but, unless collected aseptically after catheterization of the urethra, culture is usually unrewarding because of microbial contamination from the prepuce.
Because vesiculitis may have a bacterial etiology, broad-spectrum antibiotics administered at labeled therapeutic dosages are usually administered to affected bulls. There are no published controlled studies that indicate preference of a specific antibiotic for treatment. Prolonged-release antibiotics are preferable because the bull, which can become unruly, does not have to be handled daily. Because vesiculitis is an inflammation as much as an infection, NSAIDs reduce the excretion of purulent material. Transient alleviation of purulent contamination may be achieved during the treatment interval in some bulls, but the prognosis for a longterm cure is guarded to poor. This is particularly true for chronic cases. Spontaneous remission has been seen when vesiculitis was diagnosed in bulls <1 yr old. Semen contaminated with purulent material is not suitable for artificial insemination and should be discarded. Surgical removal of affected vesicles has been done but is a difficult procedure. The prognosis after surgery is fair in yearling bulls; surgery has not been successful in adult bulls with chronic vesiculitis.