M. agalactiae is a species of the Mycoplasmas genus. It causes Contagious agalactia of sheep and goats, resulting in Mastitis, arthritis and conjunctivitis following parturition. It also causes abortion and fatal pneumonia in young animals.

M.agalactiae is shed in milk and can be localised in supramammary lymph nodes. There are inactivated, attenuated vaccines available.