Potential pathogenic mechanisms include infectious agents ascending the urethra to the vesicle, descending through the ductus deferens from the testicles or epididymides, or embolic spread from infection of 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 pneumonia, systemic infection, umbilical infection or chronic soft tissue abscesses is more likely.
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 may be found during a routine breeding soundness examination but is usually first suspected after collection of a semen sample grossly contaminated with purulent material. Vesiculitis may be unilateral or bilateral. Unilateral vesiculitis is indicated by asymmetry in the size of the glands. Bilateral vesiculitis is less common and may be difficult to diagnose because both vesicles may be equally large. It is possible for a vesicle to be abscessed; in such cases, the affected vesicle is markedly larger than the other and may be fluctuant on palpation.
Rectal examination typically reveals an enlarged, sometimes irregular, and often fibrotic vesicle. Ultrasonographic diagnosis may include observation of enlarged vesicles, excess soft tissue opacities, or purulent material within the vesicles. Asymmetry of the vesicles can be detected by measuring the length and diameter of each vesicle during ultrasonography.
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.
Broad-spectrum antibiotics administered at labeled therapeutic dosages are administered to affected bulls because vesiculitis commonly has an infectious etiology. Some studies indicate better tissue concentrations of antibiotics within the seminal vesicles when administered at double their labeled dose. Prolonged-release antibiotics are preferable because of better overall tissue penetration and reduced handling of the bull. 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
