Equis ISSN 2398-2977

Semen: bacteriospermia

Contributor(s): Sarah Binns, Jean Pierre Held, Rob Lofstedt, Graham Munroe, Elaine Watson


  • Bacteria found in semen are often contaminants; these must be differentiated from pathogens.
  • Cause: many potential agents, includingTaylorella equigenitalis,Streptococcus zooepidemicus,Klebsiella pneumoniae.
  • Signs: subclinical infection unless specific infection of reproductive tract.
  • Diagnosis: microbiologic examination of swabs and ejaculate; identification of site of infection.
  • Treatment: rest from mating, antimicrobials, specific treatments for reproductive tract infections.
  • Prognosis: fair, depending on organism and site of infection.
  • Management: use of semen extender containing antimicrobials.



Predisposing factors

  • Normal commensals on penis.
  • Poor hygiene in environment.
  • Poor management, eg failure to clean sheath and penis or overzealous washing with antiseptic solutions.
  • Ascending infection from urethritis.


  • Bacterial infection elsewhere in urogenital tract.


  • Bacteriospermia may be caused by contaminating commensals or infection by potential pathogens or infections of the urogenital and reproductive tract.
  • Many bacteria in semen are commensals, which grow in penile and preputial smegma   →   normal flora discourages growth of pathogens   Penis: bacterial colonization  .
  • Bacteriospermia is rarely associated with urethritis and/or cystitis   Bladder: cystitis - bacterial  , or in extremely unusual cases, epididymitis, orchitis   Testis: orchitis - bacterial  , seminal vesiculitis, or ampullitis.
  • Bacteriospermia is rarely associated with clinical signs or lesions in the male, except that urethral lesions caused byK. pneumoniaemay lead to hemospermia   Semen: hemospermia  .
  • Most mares do not show pathology; they cope with most potentially pathogenic bacteria (non susceptible).
  • T. equigenitalis,Klebsiella pneumoniaeandPseudomonas aeruginosainfections can lead to endometritis in susceptible and non-susceptible mares.
  • Susceptible mares can become infected with bacteria shed in the sperm of covering stallions.


  • Often chronic or recurrent contamination.


  • Bacteriospermia is usually detected when mares mated to the stallion repeatedly return to estrus with acute bacterial endometritis   Uterus: endometritis - bacterial  .
  • Semen is almost inevitably contaminated with bacteria.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Watson E D (1997)Swabbing protocols in screening for contagious equine metritis.Vet Rec140(11), 268-271 PubMed.
  • Watson E D (1997)Fertility problems in stallions.In Practice19, 260-269 VetMedResource.
  • Madsen M & Christensen P (1995)Bacterial flora of semen collected from Danish Warmblood stallions by artificial vagina.Acta Vet Scan36(1), 1-7 PubMed.
  • Brinsko S P, Varner D D, Blanchard T Let al(1992)Bilateral infectious epididymitis in a stallion.Equine Vet J24(4), 325-328 PubMed.