Purple prairie clover (Dalea purpurea Vent) reduces fecal shedding of Escherichia coli in pastured cattle

Copyright © International Association for Food Protection. A 3-year (2009 to 2011) grazing study was conducted to assess the effects of purple prairie clover (PPC; Dalea purpurea Vent) on fecal shedding of total Escherichia coli in cattle. Three pasture types were used in the experiment: bromegrass (Check), mixed cool season grasses with PPC (Simple), and mixed cool and warm grasses with PPC (Complex). Pastures were rotationally grazed during a summer and fall grazing period. PPC was grazed in summer at the vegetative or early flower stage and at the flower or early seed stage during the fall. Fecal samples were collected for enumeration of E. coli and chemical analyses. Forage samples were collected throughout grazing for analysis. Condensed tannins (CT) were only detected in Simple and Complex pastures that contained PPC, with higher concentrations found in the fall than in the summer. Fecal counts of E. coli in cattle grazing Simple and Complex pastures linearly decreased (P , 0.05) over summer to fall in all 3 years, an outcome not observed in cattle grazing the Check pasture. Across the three grazing seasons, fecal E. coli was lower (P , 0.05) in cattle grazing Simple and Complex pastures than in those grazing the Check pasture during the fall. During the fall, feces collected from cattle grazing the Check pasture had higher (P , 0.05) values for pH, N, NH3-N, total volatile fatty acids, and branched-chain volatile fatty acids, but a lower (P , 0.05) acetate:propionate ratio than feces collected from cattle grazing Simple or Complex pastures. In a second experiment, two strains of E. coli were cultured in M9 medium containing 25 to 200 mg/ml of PPC CT. Growth of E. coli was linearly (P , 0.01) reduced by increasing levels of PPC CT. Scanning electron micrographs showed electron-dense filamentous material associated with the outer membrane of E. coli cells exposed to CT. Incorporation of PPC into forage reduced the fecal shedding of E. coli from grazing cattle, likely due to the anti-E. coli properties of PPC CT.