Benefits of Condensed Tannins in Forage Legumes Fed to Ruminants: Importance of Structure, Concentration, and Diet Composition

Abstract

Condensed tannins (CTs) account for up to 20% of the dry matter in forage legumes used as ruminant feeds. Beneficial animal responses to CTs have included improved growth, milk and wool production, fertility, and reduced methane emissions and ammonia volatilization from dung or urine. Most important is the ability of such forages to combat the effects of gastrointestinal parasitic nematodes. Inconsistent animal responses to CTs were initially attributed to concentration in the diet, but recent research has highlighted the importance of their molecular structures, as well as concentration, and also the composition of the diet containing the CTs. The importance of CT structural traits cannot be underestimated. Interdisciplinary research is the key to unraveling the relationships between CT traits and bioactivities and will enable future on‐farm exploitation of these natural plant compounds. Research is also needed to provide plant breeders with guidelines and screening tools to optimize CT traits, in both the forage and the whole diet. In addition, improvements are needed in the competitiveness and agronomic traits of CT‐containing legumes and our understanding of options for their inclusion in ruminant diets. Farmers need varieties that are competitive in mixed swards and have predictable bioactivities. This review covers recent results from multidisciplinary research on sainfoin (Onobrychis Mill. spp.) and provides an overview of current developments with several other tanniniferous forages. Tannin chemistry is now being linked with agronomy, plant breeding, animal nutrition, and parasitology. The past decade has yielded considerable progress but also generated more questions—an enviable consequence of new knowledge!

Activity, Purification, and Analysis of Condensed Tannins: Current State of Affairs and Future Endeavors

“…Recent studies show that the availability of these CT fractions of known purity and composition (varying PC/PD ratios and mDP values) has already been beneficial in identifying CT structural features exhibiting selectivity in the parasite larval exsheathment inhibition assay (Williams et al, 2014;Quijada et al, 2015;Mueller-Harvey et al, 2019). Improvement of existing analytical methods, along with development of new analytical techniques for CT analysis, has provided important information on structure-activity relationships.…”

“…In addition to affecting the farm N cycle, other attributes of CT-containing feedstuffs include the prevention of bloat (Li et al, 1996;McMahon et al, 2000) and their ability to act as natural antiparasitic agents (Hoste et al, 2006Quijada et al, 2015;Mueller-Harvey et al, 2019). Thus, the use of CT-containing forages and other plant material containing CTs can positively affect farm economic and environmental sustainability (Aerts et al, 1999;Piluzza et al, 2013).…”

Analysis of condensed tannins in Populus spp. using reversed phase UPLC‐PDA‐(−)esi‐MS following thiolytic depolymerisation

“…angustifolia × fremontii). 8 The MDP is an important indicator of biological activity, 10,12 and is analogous to polymer chain length when the following assumptions are met: cross-linking is absent, all non-derivatised catechin and gallocatechin monomers generated by thiolysis represent polymer termini, and thiolysis is complete. These potential interferences were evaluated to demonstrate that MDP provides a satisfactory estimate of polymer length in P. tremuloides.…”

“…polymer size, hydroxylation, and stereochemistry) are genetically-determined in Populus, 8,9 and in many plant species can influence CT biochemical properties. 1,[10][11][12] While numerous studies reveal relationships between CT concentrations and ecological effects in Populus, and CT structures have been related with biological properties in other plants, studies relating variations in CT structures with biological effects in Populus are lacking. Accessibility of methods for analysing CT structures will likely facilitate investigating variations in CT polymer size, hydroxylation, and stereochemistry in this genus.…”

The Value of Condensed Tannins in Forages: Overview of the Symposium

“…Professor Irene Mueller-Harvey from the University of Reading, Berkshire, UK, continued the discussion of techniques used to identify, characterize, and quantify CT (Mueller-Harvey et al, 2019). The quantification of tannins by thiolysis in processed forages such as hay or silage, where tannins become more tightly bound, is aided by the inclusion of NaOH.…”