Bioactive Tannins in Forage Legumes: Myths, Ignorance and Aspirations.

Abstract

Tannin-containing legumes have attracted much interest due to their animal health and nutritional benefits. Although several tannins are anti-nutritional, a few can generate valuable benefits for controlling parasitic nematodes that are resistant to anthelmintic drugs, for improving protein utilization by ruminants and fatty acid profiles in meat and milk products and for reducing greenhouse gases. A 5% dietary maximum limit of tannins has been suggested, but information on structure-activity relationships are essential in order to fully exploit the potential of these natural plant compounds. Breeders also require guidelines and screening tools for optimal tannin compositions, and farmers require tannin-containing forages that provide consistent results.

Plants vary in tannin contents and composition depending on species, variety and growing conditions. Recent research in Europe (‘LegumePlus' and other projects) has focused on new tools for analyzing soluble and insoluble tannins in plants, silages and digesta. This involved isolating different types of tannin standards from a wide range of different plants and thiolysis to assess their purity and composition. We also developed new UPLC-MS/MS, NIR- and NMR-analysis methods and tested tannin-protein interactions. Agronomists and plant breeders assembled germplasm collections, identified sainfoin-specific markers, and strategies for weed control. Ruminant nutritionists studied in vitro and in vivo fermentations, N-balances and the quality of meat and milk products. Parasitologists explored the anti-parasitic properties using a wide range of different tannin types.

The presentation will summarize current knowledge and conclude with a wishlist for ‘ideal' tannin-containing forages. It will emphasize that robust and stable tannin concentrations and compositions are required in addition to high yield, good weed suppression and resistance to climatic stress.