Influence of chlortetracycline feeding on salmonellosis in calves. I. Rate and duration of shedding. II. Severity of illness.

Studies were conducted to test the influence of the feeding of chlortetracycline (CTC) on the fecal shedding of S. typhimurium subsequent to experimentally induced infection in calves. Levels of 0, 20, 50, and 100 gm CTC per ton of feed were fed to groups of calves for a two-week period before inoculation and the resulting level of shedding of S. typhimurium quantified. At the 50 gm/ton level, the feeding of CTC was associated with a significantly higher level of shedding than in non-CTC fed controls, and the duration of shedding was longer. Calves fed at 50 and 100 gm CTC/ton were affected much more severely by the inoculation than calves receiving no CTC. The same was true to a lesser extent in the calves fed 20 gm/ton. Observations made on each calf included changes in body temperature, time of onset, severity and duration of diarrhea, straining, and anorexia. Since the fecal output of salmonellae is increased at the level of 50 gm/ton, the authors conclude that this commonly used level of CTC feeding in calves contributes to the size of the salmonella reservoir in nature, thus increasing the risk of exposure to both man and animals alike and otherwise complicates the problems of salmonellosis.