Host immunity and the colon microbiota of mice infected with Citrobacter rodentium are beneficially modulated by lipid-soluble compounds from late-cutting alfalfa in the early stages of infection

Alfalfa is a forage legume commonly associated with ruminant livestock production that may be a potential source of health-promoting phytochemicals. These benefits can be obtained by feeding whole or extracted alfalfa with varying effects on underlying host immunity and the intestinal microbiota. The objective of this study was to measure body weight (BW), average daily feed intake (ADFI), host immunity, and the colon microbiota in mice fed hay, aqueous, and chloroform extracts of early (1st) and late (5th) cutting alfalfa before and after challenge with Citrobacter rodentium. 5th cutting alfalfa was shown to improve BW at 5 and 6 days post-infection compared to 1st cutting alfalfa (P = 0.02 and 0.01). Immediately following inoculation, 5th cutting chloroform extracts significantly reduced the relative abundance of C. rodentium (P = 0.02) and did not display the early lymphocyte recruitment observed in 1st cutting extract. In later infection timepoints, both chloroform extracts maintained reduced splenic B-cell and macrophage populations while increasing the relative abundance of potentially beneficially genera such as Turicibacter (P = 0.02) and Akkermansia (P = 0.04 and 0.02) compared to the control diet. These results suggest that lipid soluble compounds enriched in late-cutting alfalfa modulate pathogen colonization and early immune responses to Citrobacter rodentium, contributing to protective effects on body weight.