Aromatic-dependent Salmonella typhimurium are non-virulent and effective as live vaccines.

The paper describes the clinical, bacteriological and pathological findings in experimental Salmonella typhimurium infection in calves. Oral doses of 10(8) and 10(9) organisms produced clinical disease and high mortality; doses ranging from 10(4)--10(7) organisms were less consistent in their action. Jersey calves appeared more susceptible to infection than Friesian calves. The clinical signs in most calves were pyrexia and a characteristic diarrhoea that lasted for up to 11 days; more severe symptoms were seen in the calves that received the higher doses. Following infection, all calves excreted S typhimurium in their faeces, the highest counts being observed in the calves that died. In the calves that survived, counts ranging from 10(2)--10(5)/g faeces occurred continuously for up to a maximum of 20 days and subsequent intermittent excretion occurred in a number of calves. In the calves that died, necrotic enteritis in the ileum and large intestine was the most striking lesion; lesions were uncommon in other organs. The findings are discussed in relation to the pathogenesis, diagnosis and control of the disease.