Abstract
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.
Highlights
The use of legume forages in livestock farming decreased in Europe over the last two decades principally because of the low price of soyabean meal and the increasing use of corn silage (Doyle and Topp 2004; Peyraud et al 2009).in the last few years there is increasing interest for temperate legumes such as birds foot trefoil (Lotus corniculatus) and sainfoin (Onobrychis viciifolia)
In LcB the average relative content of the soluble Condensed tannins (CT) fraction was with 70% the most abundant fraction, whereas the relative content of the protein- and fibre-bound fractions was 18 and 12% lower (P < 0.05), respectively
The present study demonstrated that the plant species and the different modes of conservation can affect quantitatively as well as qualitatively total CT content as well as the relative portion of the three CT fractions of forages
Summary
In the last few years there is increasing interest for temperate legumes such as birds foot trefoil (Lotus corniculatus) and sainfoin (Onobrychis viciifolia). Apart from their crude protein content, the content on bioactive secondary metabolites like condensed tannins (CT) attracts great interest. Condensed tannins have been shown to improve health, production efficiency and product quality in ruminants. Feeding CT can modify the quality of ruminant products by increasing n-3 polyunsaturated fatty acid levels and by reducing pastoral off-flavour (Schreurs et al 2007; Girard et al 2015, 2016)
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