An immunogenic composition comprising an attenuated, avirulent Mycoplasma bovis bacterium strain wherein the bacterium is passaged more than 110 times, wherein the attenuated, avirulent Mycoplasma bovis strain is selected from the group consisting of: The attenuated M.bovis strain deposited with the ATCC under accession number PTA-9666 or M.bovis strain with the same characteristics or The attenuated M.bovis strain deposited with the ATCC under accession number PTA-9667 or M.bovis strain with the same characteristics or any attenuated, avirulent Mycoplasma bovis bacterium strain having the characteristic that its administration to a group of non-human animals in the form of a live vaccine reduces the mortality and euthanization rate in the group of animals by at least 56% as compared to a non-vaccinated control group of animals after the administration of a single dose of said vaccine.
