Abstract
A natural outbreak of Salmonella saint-paul infection in two Institute herds was monitored clinically, bacteriologically and immunologically. This paper describes the findings in calves. Morbidity and mortality became apparent 30 days after S. saint-paul was first isolated on routine sampling of neonatal calf faeces. All heifer calves were treated with a tetracycline or ampicillin preparation when they showed clinical signs of disease, while the effects of intradermal vaccination with heat-killed S. saint-paul were assessed in a proportion of the bull calves. Antibiotic treatment reduced mortality and the number of persistent excretors; vaccination did not affect mortality but, if given during the first week of life, reduced the duration of faecal excretion. Calves which were untreated and unvaccinated, or vaccinated when older than 16 days, excreted S. saint-paul for periods of up to 18 months. Of six 'recovered' calves, which had been negative on faecal culture for 5-8 weeks, four yielded S. saint-paul at necropsy. Agglutinating antibody titres were highest in those unvaccinated calves which were persistent excretors.