Mycoplasma bovis is a challenging problem in affected herds. It is widespread in NI and can cause respiratory disease in calves, arthritis and mastitis, either as a sole cause or in association with other organisms. Disease may not appear for several weeks or months after a carrier is introduced into the herd, and the introduction of Mycoplasma bovis can result in severe outbreaks of pneumonia that do not respond to treatment. However some steps can be taken to reduce the risk of spread.