Feed value for ruminants of legume forages containing condensed tannins in temperate environment

This review focuses on the state of knowledge of the content, biological activity, and structure of condensed tannins in tannin-rich legume forage species from temperate areas as well as the factors that influence these parameters. The effects of condensed tannins on feed intake, digestibility of organic matter and crude protein in the rumen and the intestine of ruminants are reviewed. With the exception of big trefoil, condensed tannins little affect intake and digestion of organic matter. In contrast, the digestibility of crude protein is always reduced in the presence of condensed tannins. The decrease in crude protein degradability in the rumen is rarely matched by better utilization of amino acids in the intestine. However, the amount of nitrogen retained by the animal is not diminished which is positive for ruminant nutrition, and the part of nitrogen excreted in urine is generally reduced. The decrease in methane eructed and urinary nitrogen excreted observed for these forages are in favor of reducing greenhouse gas emissions and limiting losses through leaching and volatilization. Finally, the energy value and the PDIE values estimated from recent measurements are consistent with the references provided in the INRA 2007 Tables. In contrast, the PDIN values should be reduced by 10 to 20 g/kg DM compared to the values of INRA 2007 Tables.