Does Total Condensed Tannin Concentration Predict Protein-Precipitating Ability of Condensed Tannins From Warm-Season Perennial Legumes?.

The primary biological activity of condensed tannins (CT) is that they bind to proteins. Condensed tannin-protein complexes are stable at ruminal pH and dissociate in the acidic pH environment of the abomasum. Ruminants consuming forage containing biologically active CT could experience an increase in the overall efficiency of protein utilization due to decreased ruminal protein degradation, more plant protein entering the gastrointestinal tract and increased intestinal absorption of amino acids. The objective of this study was to determine if the total CT (TCT) concentration of warm-season perennial legumes could predict the biological activity of CT relative to protein-precipitating ability. Leaves from Leucaena retusa, Desmanthus illinoensis, Lespedeza stuevei, Mimosa strigillosa, Neptunia lutea, Acacia angustissima var. hirta, Desmodium paniculatum, Arachis glabrata, and Lespedeza cuneata were evaluated for both TCT and protein-precipitable phenolic (PPP) concentration. Condensed tannin concentrations were determined by the butanol-HCl method and quantified using species-specific standards. Protein-precipitable phenolic concentration was determined by reacting forage extracts with bovine serum albumin. Desmodium paniculatum had the greatest TCT at 12.46%, whereas Arachis glabrata had the least (0.57%). The PPP concentration was greatest for Desmodium paniculatum (139.9 g/kg DM) and least for Arachis glabrata (0.0 g/kg DM). Regression analysis of PPP on TCT showed a strong-positive correlation (R² = 0.81; P < 0.0001) suggesting that the use of TCT to predict protein-precipitating ability of forage CT has promise.