Swabbing the Urethral Diverticulum.
Swabbing of the urethral orifice is a standard practice during breeding soundness examination of the stallion, for evaluation of the possibility that the urethra and tract have been colonized with bacteria that cause metritis in the mare. The urethra is swabbed before and after semen collection, and the semen is also cultured. The purpose of the swab is to identify stallions with penile skin flora made up of a monoculture of Pseudomomas or Klebsiella, or other putative metritis pathogens.
Asbury AC (1988)