This invention provides an immunogenic composition including a soluble portion of a Mycoplasma hyopneumoniae (M.hyo) whole cell preparation, wherein the soluble portion of the M.hyo preparation is substantially free of both (i) IgG and (ii) immunocomplexes comprised of antigen bound to immunoglobulin.本發明提供包括豬肺炎黴漿菌(Mycoplasma hyopneumoniae,M.hyo)全細胞製劑之可溶部分之免疫原性組合物,其中該豬肺炎黴漿菌製劑之該可溶部分實質上不含(i)IgG與(ii)由結合至免疫球蛋白之抗原組成之免疫複合物二者。