BACKGROUND: The primary objective of this study was to confirm the infection status of Ureaplasma diversum in Australian bulls and to identify morphological changes of sperm from U. diversum-positive bulls.METHODS: Fresh semen samples were taken from 29 sexually active beef bulls from suspect herds in the Riverina/Upper Murray region. U. diversum was identified using PCR analyses and culture of the organism.RESULTS: Nine of the bulls were PCR-positive for U. diversum but none of these had genital lesions. Sperm from infected bulls showed increased incidence of abnormal tails (bent and coiled), as well as surface abnormalities (i.e. small protuberances or lumps).CONCLUSIONS: The results suggest impairment of sperm function and possibly fertility. Further investigations into the potential role of U. diversum as a pathogen for Australian cattle are warranted.