Cultivating Lawsonia intracellularis (LI) bacteria comprises: (a) incubating the bacteria at an oxygen concn. of 18% and (b) maintaining the bacteria in suspension, to cultivate the bacteria. Also claimed are: (1) a method for cultivating LI bacteria comprising: (a') inoculating culture cells with an inoculum comprising LI bacteria so as to infect the cells with the bacteria and (b') incubating the infected cells at a temp. of 36 -38 [deg]C in an oxygen concn. of 0-8% while agitating the infected cells so as to cultivate the LI while maintaining the infected cells in suspension； (2) a method for producing an attenuated LI strain comprising: (i) obtaining culture cells infected with LI bacteria, (ii) incubating the infected cells at an oxygen concn. of 0-18%, (iii) agitating the infected cells so as to cultivate the bacteria while maintaining the infected cells in suspension, (iv) passaging at least a portion of the cultivated bacteria and (v) selecting for an attenuated strain to provide an attenuated LI bacteria； (3) a vaccine for inducing an immune response to LI bacteria in an animal comprising an attenuated strain of LI in a carrier, where the attenuated strain is in amt. effective to produce an immune response.
