Inoculation experiments with Bordetella bronchiseptica strains in SPF pigs.

The progeny of 9 SPF gilts fed a balanced ration (Table I) was used in an inoculation experiment with field strains of Bordetella bronchiseptica isolated in herds suffering atrophic rhinitis. Acute rhinitis was produced within a week after intranasal inoculation of B. bronchiseptica into 1 to 11-day-old piglets. Coughing occurred in some of the exposed pigs, but signs of pneumonia did not develop. A few pigs were killed at intervals of 1 to 3 weeks after exposure. These pigs all showed histological lesions in the turbinate and B. bronchiseptica was recovered from various parts of the respiratory tract. Pigs killed 3 weeks after inoculation showed advanced turbinate atrophy (Tables II and III). Among inoculated litter mates reared to slaughter weight, only one developed clinical signs (slight) of atrophic rhinitis, and a tendency towards an elimination of the B. bronchiseptica infection from the accessible part of the nasal cavity was noticed during the growth period. By examination of nasal swabs collected when the pigs were 10 to 13 weeks old, Mycoplasma flocculare was isolated as well from pigs inoculated with B. bronchiseptica as from the control pigs. The growth rate of the experimental pigs was high and no difference in feed consumption or feed conversion occurred between the exposed pigs and the control pigs. By post mortem examination of the snouts from the pigs slaughtered at approx. 85 kg live weight, severe atrophic rhinitis was not found. Approximately one third (32%) of the exposed pigs showed slight atrophic rhinitis lesions (Table IV). The results are discussed and it is concluded that the isolated B. bronchiseptica strains are pathogenic in young pigs and able to induce turbinate atrophy 2 to 3 weeks after inoculation. Turbinate atrophy induced in pigs a few weeks old, may apparently restore completely or almost completely during the growth period. Under the provided experimental conditions, infection with B. bronchiseptica did not result in the development of a lasting, growth-retarding atrophic rhinitis.