Antimicrobial resistant Salmonella are becoming more prevalent. Therefore, alternative methods to control swine Salmonella infection must be explored. We examined whether feeding lactic acid to swine is an effective way to control clinical and subclinical Salmonella Typhimurium infection in these animals. In this experiment, swine were inoculated with 5.6 x 10(7) CFU (hi-ST) or 5.6 x 10(5) CFU (lo-ST) of S. Typhimurium per swine to reproduce clinical and subclinical infection. The swine were either fed a commercial feed supplemented with 2.8% lactic acid (LA) or the commercial feed without supplementation (C) to examine the effect of feeding lactic acid. Twenty 21 and 22 days old swine were divided into 4 groups, LA-hiST, C-hiST, LA-loST and C-loST, and fed the respective feed. They were inoculated S. Typhimurium at 51 and 52 days old. Clinical symptoms and the number of S. Typhimurium shed in feces were evaluated. The LA-hiST group did not show obvious clinical symptoms, such as diarrhea or febrile response, but the C-hiST group did show clinical symptoms. The number of S. Typhimurium shed in the feces of the LA-hiST group was lower than in that of the C-hiST group, and that of the LA-loST group was lower than that of the C-loST group. Our data suggest that dietary supplementation with 2.8% lactic acid can be an effective way to control clinical and subclinical infections of S. Typhimurium in swine.