Protection of cattle against experimentally induced salmonellosis by intradermal injection of heat-killed Salmonella dublin.

A single intradermal dose (7.5 mg) of heat-killed Salmonella dublin protected two out of three cattle against intravenous challenge with live S dublin. A second dose of 8 mg increased the protection rate to six out of seven. Four of the survivors had transient diarrhoea and S dublin was recovered from the carcases of four killed at four to 21 weeks after infection. Protected animals had elevated serum antibody titres and their serum passively protected rats against intraperitoneal challenge. The resistance of vaccinated cattle, presumably immunological in character, was not associated with leucocyte migration inhibition by salmonella antigen, depression of serum iron levels or haematological changes.