Etiology

• A variety of pathogens have been isolated:
  • Viruses.
  • Bacteria including:
  • Trueperella pyogenes Trueperella pyogenes.
  • Histophilus somni Histophilus somni infection.
  • Gram-negative anaerobes.
  • Chlamydia Chlamydia spp.
  • Ureaplasma Ureaplasma diversum.
  • Mycoplasma Mycoplasma bovis.
  • Protozoa.
  • Also Brucella abortus Brucella abortus in regions where this pathogen is not well controlled.
• Ascending or descending infection from the urinary or reproductive tract and hematogenous spread have been postulated.
• Possibly urine reflux leading to inflammation.

Pathophysiology

• In the normal bull, the paired seminal vesicles lie either side of the urethra and ampullae about 18-20 cm cranial to the anal sphincter.
• They are movable, may be oblong or oval shaped, are about 10 x 5 x 3 cm in size, and the surface texture feels similar to bubble wrap on rectal palpation .
• A definite pathophysiology has not been determined.
• One or both glands may  be affected.
• A link to carbohydrate-rich diets is postulated, with hematogenous spread from rumenitis or liver abscessation. However, the condition is also reported to occur in grass-fed animals in South America.
• The concurrent presence of epididymitis or orchitis Orchitis and epididymitis in some bulls suggests that descending infection from the reproductive tract may occur.
• Ascending infection from urethral infection, for example caused by bulls riding each other, is a possibility. Close confinement of bulls in groups may contribute to increased riding behavior and therefore increased risk of vesiculitis.
• Reflux of semen or urine into the gland as a result of an asynchrony in the ejaculatory process or congenital anatomical abnormalities in the region has been suggested as another possible cause.

Epidemiology

• Average incidence of 2-4% based on bull breeding soundness examinations is reported, but can be 60-80% in individual groups of bulls or herds.