Outbreaks of Salmonella newport infection in dairy herds and their relationship to management and contamination of the environment.

Two outbreaks of Salmonella newport infection in dairy herds are described which were characterised by haemorrhagic enteritis. The history of the outbreaks, the extent of the losses, clinical and laboratory findings and treatment are described. The first herd consisted of 193 cattle, of which seven died, three aborted and another 84 required treatment. Salmonellosis persisted over 14 months throughout the summer on a paddock grazing system and continued during the following winter when the herd was loose housed. The relationship of the commencement of clinical disease to dietary changes and to the time of calving is described, as are the problems in controlling the disease. The second herd consisted of 98 milking cows and a few beef animals. One cow died and two aborted; altogether 18 were clinically affected. The epidemiology of the disease and the geographical relationship between the two farms is described. Extensive contamination of streams occurred and one cow died on a neighbouring third farm. In contact humans were found to be excreting the organism. The public health significance of the outbreak is discussed because bulk milk samples were contaminated with salmonellae for 10 months and local streams were polluted with human sewage.