Modification of the proportion of extractable and bound condensed tannins in birdsfoot trefoil (Lotus corniculatus) and sainfoin (Onobrychis viicifolia) during wilting, ensiling and pelleting processes

Condensed tannins (CT) in legume forages vary not only in concentration and structure, but also in the portion of soluble and protein- and fibre-bound fractions. This study aimed to assess the changes in the total CT level as well as relative abundance of the three CT fractions from fresh to wilted, ensiled or pelleted legumes like in birds foot trefoil (two cultivars) and in sainfoin (one cultivar). Each legume underwent three consecutive harvests, of which the first two were wilted. Additionally, wilted legumes were either ensiled (first harvest) or transformed into dehydrated pellets (second harvest). For each harvest, total CT and the percentage of soluble, protein- and fibre-bound CT differed (P < 0.01) among plants. The total CT content was similar after wilting but was lower (P < 0.05) after ensiling. After wilting, ensiling and pelleting the portion of soluble CT was lower in favour of protein-bound CT portion. However, time of harvest affected (P < 0.05) total CT and the percentage of soluble and protein-bound CT. Thus, measuring the bound-fraction should not be ignored in the determination of CT content since this fraction, together with the soluble fraction, might protect protein from ruminal degradation.