Combined experimental infections with Bordetella bronchiseptica and either a toxigenic or a non-toxigenic strain of P. multocida were carried out in newborn specific pathogen-free piglets born to 25 sows. Pigs inoculated with B. bronchiseptica and toxin-producing P. multocida developed severe progressive atrophic rhinitis corresponding to the natural disease. Vaccination of sows with a toxin-containing P. multocida vaccine significantly reduced the increase of nasal turbinate lesions in the offspring.