| Acacia angustissima is a nitrogen-rich legume with potential as a feed supplement to improve ruminant production, but is toxic to ruminants. It was determined that rats are sensitive to the anti-nutritional factors and could be used as a model to evaluate the plant. Extracting leaf material with a variety of solvents indicated that extracts containing polyphenolic compounds reduced intake and average daily gain. Salivary gland dry weight, fecal nitrogen excretion and concentrations of proline, glycine and glutamic acid in the feces were also increased. The effect on intake and average daily gain was ameliorated by the addition of polyethylene glycol, which complexes with polyphenolic compounds. Non-protein amino acids or other plant components did not contribute to the anti-nutritional effect in rats. Analysis of polyphenolics by mass spectrometry and nuclear magnetic resonance indicated the presence of condensed tannin (proanthocyanidin) dimers to pentamers based on guibourticacidin, fisetinidin and catechin, with fisetinidin units predominating.; Tannin-resistant bacteria may prevent detrimental effects caused by high concentrations of dietary tannins in animal feed, but little is known about the effect of tannins on bacteria in the gastrointestinal tract. Counts of tannin-resistant and total fecal bacteria and metabolic fingerprinting of the fecal community were used to determine the effect of tannins on the culturable bacteria. Molecular fingerprinting by Denaturing Gradient Gel Electrophoresis (DGGE) and quantification of bacterial groups by dot blot hybridization of 16S rRNA genes were used to include the effect on non-culturable bacteria. Condensed tannins altered bacterial populations resulting in a shift in predominant bacteria towards tannin-resistant Gram-negative Enterobacteriaceae and Bacteroides species. Metabolic fingerprint patterns revealed that functional activities of culturable fecal bacteria were affected by the presence of tannins. Altered bacterial populations could still be distinguished 3.5 weeks post-tannin.; To increase the proportion of tannin-resistant bacteria it is necessary to know the mechanism of tannin-resistance. Wattle condensed tannins were determined to be toxic to Escherichia coli in aerobic medium primarily because they generate hydrogen peroxide. The oxidative stress response helps E. coli strains to overcome this inhibitory effect. |
