Salmonella dublin infection of calves: use of small doses to simulate natural infection on the farm.

Small numbers of Salmonella dublin were used to infect calves in an attempt to simulate natural infection on the farm. Twenty calves were exposed to S. dublin by one or more of the following methods: Sucking cows which were excreting S. dublin in their faeces (less than 10(2)-10(5) organisms/g). Housing on S. dublin contaminated bedding. Drinking S. dublin contaminated water (10(2)-10(4) organisms/ml). During this experiment some calves were given therapeutic does of oxytetracycline. After exposure the calves were examined for faecal excretion of S. dublin (in some instances mouth swabs and blood samples were also examined) and for clinical signs of illness. Most of the calves became infected with S. dublin but excretion was usually sporadic and the numbers of salmonellas excreted were small. No clinical signs of salmonellosis were observed by S. dublin was isolated from one calf at post-mortem. Another six calves, dosed orally with either 10(6) or 10(8) S. dublin, showed signs of mild illness and although three calves had diarrhoea excretion of salmonellas was intermittent. S. dublin was isolated from one of these calves at post-mortem.