Development of the genital microflora in stallions used for artificial insemination throughout the breeding season.

An important factor influencing stallion fertility is the microbial contamination of semen. Aims of this study were to investigate changes in the microbiological population of the genital mucosa and semen in artificial insemination stallions (n=16) from before to after one breeding season (February-August). MALDI-TOF-MS (matrix assisted laser desorption/ionization time-of-flight mass spectrometry) was used for identification of microbial agents. For bacteriology, swabs from the urethral opening, urethral fossa and penile sheath as well as semen were collected at 4-week-intervals. For semen motility and percentage of morphologically normal spermatozoa, changes over time (P<0.001) occurred. In 14.3% of genital swabs and 25.0% of ejaculates no microbial growth was found. Intensity of total microbial growth increased throughout the breeding season (P<0.001). From the penile sheath, between 1.4±0.1 microbial species in February and 3.3±0.4 in August were identified. From semen, 1.1±0.3 microbial species in February and 2.9±0.6 in August were obtained. The number of microbial species isolated from the sheath of the penis (2.0±0.1) and urethral fossa (2.0±0.1) was greater (P<0.01) compared with the urethral opening (1.6±0.1) and semen (1.5±0.1). The microbial flora consisted of aerobic and anaerobic bacteria, dominated by coagulase-negative staphylococci, alpha-haemolytic streptococci and coryneforms. Only occasionally potentially pathogenic agents (E. coli, Ps. aeruginosa) were found. The microbial flora was not related to seminal characteristics.