A composition for eliciting an anti-Mycoplasma hyopneumoniae immune response in an animal, said composition comprising an immunologically effective amount of a live avirulent strain of Mycoplasma hyopneumoniae and the biologically acceptable adjuvant SP-Oil, wherein the live avirulent strain of Mycoplasma 5 hyopneumoniae is a strain whose genome comprises a nucleic acid sequence having at least 95% homology to the nucleic acid sequence of a reference Mycoplasma hyopneumoniae J strain having the GenBank Accession Number AE017243.
