Bovine salmonellosis: experimental production and characterization of the disease in calves, using oral challenge with Salmonella typhimurium.

A highly virulent strain of Salmonella tyhimurium was given orally to produce disease experimentally in 21 normal colostrum-fed calves 3 to 9 weeks old. The challenge inoculum varied from 10(4) to 10(11) organisms. The disease was characterized by fever, depressed attitude, and decreased appetite. Many calves given larger challenge dose levels also had diarrheic feces containing mucus, fibrin, and blood. Fecal cultures were positive for salmonella. Septicemia occurred in some calves (9 of 15 calves cultured were positive). Eleven calves died and 10 calves survived challenge exposure. Survival was inversely related to the size of the challenge inoculum and directly related (although to a lesser degree) to age of the calf. White blood cell total and differential counts were variable. Both neutropenia and neutrophilia were observed. Plasma proteins decreased markedly in calves with diarrhea, probably indicating fecal protein loss. Fibrinogen increased during the acute stages of diarrhea.