Technical Abstract: Calves often succumb to Salmonella enterica, Dublin after maternal antibody protection has abated. Enhancement of innate immunity or earlier maturation of adaptive immunity to support vaccinations with dietary immune modulators may be the best option for protection during this vulnerable period. In this study, effects of beta-glucan plus ascorbic acid on adherence and pathogenicity of S. Dublin and the innate immune response in neonatal calves were examined. From d 3- until approximately d 18-of-age, 20 calves were placed on control diets (no supplement) or supplemented diets (beta-glucan added at 0.9 g/d plus ascorbic acid 500 mg/d). At 21 d-of-age, 5 calves per treatment received 2 x 10^8 CFU of S. Dublin orally. Calves were euthanized and samples collected 48 h after the S. Dublin challenge. Weight gain was greater for supplement calves than unsupplemented-control calves and than supplemented calves given the challenge, with interaction of supplement and challenge (P = 0.01) and main effect of supplement (P = 0.04). By 24 h, challenged calves had rectal temperatures that were greater (P < 0.05) than control calves, an even greater difference was observed by 48 h. The frequency of calves with a fecal score greater than 3 was most for the challenge calves compared with all other treatments (P = 0.01). Microbial analysis showed a quick spread of S. Dublin through the intestinal tissues into mesenteric lymph nodes, and into spleen and lung tissues within 48 h. An ex-vivo challenge of control and supplemented-control calves with Salmonella enterica, Typhimurium, showed no difference between treatments nor between jejunal and ileal tissues. Supplement decreased IL-1 receptor antagonist expression in liver tissues (P = 0.05) and tended to increase TLR4 (P = 0.056) and IL-12 (P = 0.077) in lung tissues. Leukocyte cell surface markers showed changes in lung cells, but not in blood leukocytes, mesenteric lymph nodes, or spleen cells. Part of the LPS receptor (CD14) was greater (P < 0.05) in lungs of calves receiving the supplement and challenge together, but not separately. Fluorescence of adhesion molecule, CD18, was expressed more (P < 0.05) in lungs of challenged than control calves, but was not different than supplement-control calves. Percentage of cells expressing DEC205 (found on maturing dendritic cells) was greatest (P < 0.05) for lung cells of supplement calves compared to the other 3 treatments and cells from S. Dublin challenged calves expressed more DEC205 (P < 0.05) than control calves. In contrast, DC205 fluorescence of positive cells was only greater (P < 0.05) for challenged calves with and without supplement. These data show that S. Dublin only briefly inhabits the intestinal tract and quickly moves to spleen and lung tissues. Lung tissue was the tissue most affected by the challenge and supplementation with beta-glucan and ascorbic acid. The beta-glucan and ascorbic acid supplement may alter the response to S. Dublin in neonatal calves by activating immune cells, particularly dendritic cells, in lung tissue.