| Summary: | Tall fescue (<i>Schedonorus arundinaceus</i> (Shreb.) Dumort) is a cool-season forage grown in the mid-south United States of America that has the potential for spring silage. Ergovaline produced by the fungal endophyte <i>Neotyphodium coenophialum</i> is preserved in tall fescue silage and can induce tall fescue toxicosis in livestock. Condensed tannins, such as quebracho (<i>Schinopsis quebracho-colorado</i> (Schltdl.) F.A. Barkley and T. Meyer) extract, can bind to the nitrogenous components of ergovaline, rendering it ineffective in the ruminant. Quebracho tannin (QT) can also bind to crude protein, reducing its conversion to ammonia. Quebracho tannin was either not added (0QT) or added at 10 (10QT) or 20 (20QT) g/kg of dry matter (DM) of silage to chopped endophyte-infected tall fescue of 670 g/kg of moisture (high moisture, HM) and 440 g/kg of moisture (low moisture, LM). A moisture × QT interaction affected the final pH (<i>p</i> = 0.02), with the lowest pH observed in HM silages with 0QT and 10QT. The ergovaline concentrations were not significantly different (<i>p</i> = 0.19) among the post-ensiled forages. Ammonia concentrations (g/kg DM) were affected by a moisture × QT interaction (<i>p</i> = 0.05), with greater concentrations observed in HM 0QT compared with HM 10QT, HM 20QT, and LM 20QT. Lactic acid concentrations (g/kg DM) decreased (<i>p</i> = 0.05) with the addition of QT. The moisture × QT interaction (<i>p</i> = 0.02) resulted in higher concentrations of acetic acid in the HM silages with 0QT and 20QT compared to the LM silage with 20QT. The total acid concentrations (g/kg DM) were higher (<i>p</i> < 0.01) at HM but did not differ (<i>p</i> = 0.54) across the QT concentrations. Ensiling tall fescue with quebracho tannin did not reduce the ergovaline concentrations, although proteolysis was reduced at the inclusion of 10 g/kg of QT in the HM silages and 20 g/kg of QT in the LM silages. The results indicate that QT as a tall fescue silage additive showed promise for modifying silage characteristics but it did not reduce ergovaline concentrations at the low QT levels used in this study.
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