The epidemiology of a feed-associated Salmonella serotype (Salmonella Yoruba) was compared with that of a ‘classical’ serotype (Salmonella Typhimurium) by inoculating pigs aged 10 weeks with 0·65 × 103, 0·65 × 106 or 0·65 × 109 colony-forming units (cfu) of either serotype. The pigs were then monitored for eight weeks with respect to the faecal excretion of Salmonella species and the presence of serum antibodies. Only minor differences were observed between the two serotypes but the dose inoculated had significant effects. The pigs inoculated with 0·65 × 109 cfu shed Salmonella species in faeces constantly for four weeks, and intermittently during the subsequent four weeks; the pigs inoculated with 0·65 × 106 cfu shed Salmonella species intermittently for four weeks, but not for longer, and the pigs inoculated with 0·65 × 103 cfu generally did not excrete Salmonella species. The pigs inoculated with 0·65 × 109 cfu S Typhimurium seroconverted at a high titre within two weeks, the pigs inoculated with 0·65 × 106 cfu seroconverted later and with lower titres of antibodies, and the pigs inoculated with 0·65 × 103 cfu did not seroconvert. A similar pattern was observed with S Yoruba, but the responses were slower and at lower titres.
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