Effect of efrotomycin in feed on the quantity, duration, and prevalence of shedding and antibacterial susceptibility of Salmonella typhimurium in experimentally infected swine.

The influence of efrotomycin administered at the rate of 16 mg/kg of feed in 10 Salmonella typhimurium-inoculated pigs was determined by comparing this group with a group of 10 pigs inoculated with S typhimurium that were given nonmedicated feed. Two control groups of 4 noninoculated pigs each, 1 group medicated with efrotomycin at 16 mg/kg of feed, the other nonmedicated, also were evaluated. An inoculum of 1.7 x 10(10) colony-forming-units/pig induced colonization of S typhimurium in all 20 pigs. Evaluation of the quantity of shedding did not reveal a clear or consistent treatment-related increase in S typhimurium counts; mean differences between the nonmedicated and medicated groups never exceeded 1 log unit. On the last day of the study (day 56 of the medication), 8 nonmedicated and 9 medicated pigs were determined to be infected with S typhimurium via enrichment procedures, so there was no difference in duration of shedding, and there were no significant differences in prevalence of shedding between the nonmedicated and medicated groups at any of the sampling times. Of 1,340 S typhimurium colonies isolated from the nonmedicated and medicated groups, 1,330 were susceptible to all 12 antibacterials tested, indicating no treatment-related effect on susceptibility. At necropsy, S typhimurium was not isolated from any liver or spleen specimens, and was isolated from only 2 of 20 lymph nodes. However, S typhimurium was isolated via enrichment from the cecal contents from all 20 pigs. There were no treatment-related differences in feed consumption, weight gain, or feed efficiency. Appreciable differences in the measurements were not found between the efrotomycin-medicated and nonmedicated pigs.