Semen as a source of Mycoplasma bovis mastitis in dairy herds.

•Contaminated semen transmitted Mycoplasma bovis infection into naive dairy herds, causing mastitis outbreaks.•The infection source was identified by epidemiological analysis and cgMLST analysis of M. bovis isolates.•The antibiotics used in semen extenders should be re-evaluated or tested M. bovis-free semen should be available.