The role of condensed tannins in ruminant animal production: advances, limitations and future directions

Abstract

-Tannins represent one of the most abundant polyphenolic compounds in plants. Tannins exist as a multitude of chemically unique entities in nature. The most commonly occurring tannins are typically divided into two major classes based on chemical structure: hydrolysable (HT) or condensed tannins (CT). Hydrolysable tannins are esters of gallic or ellagic acid linked to a polyol core, typically glucose. Condensed tannins or proanthocyanidins consist of flavan-3-ol subunits linked together to form oligomers and polymers. Both HT and CT are defined as astringent, medium-to-high-molecular weight polyphenolic compounds that characteristically bind and precipitate soluble proteins. The objective of this paper was to present recent advances in CT-ruminant interactions, the limitations associated with understanding and using CT in ruminant animal production, and future needs for research to further advance our knowledge of the role of CT in optimization of ruminant animal production. Condensed tannins pose some anti-nutritional problems to ruminants due to their astringent property that reduces feed intake and, consequently, animal performance. Ruminants can, however, tolerate CT by slowly adapting the ruminal microbes to the toxic effects of CT and by releasing CT-binding salivary proteins. The protein-binding ability of CT has some benefits to the ruminant due to complexes formed with essential amino acids, preventing their degradation in the rumen, but releasing them in the lower gut for absorption by the animal. Recent data have suggested increased N retention when CT is given to growing animals. There are potential benefits of using CT and HT for anthelmintic purposes due to their ability to inhibit egg hatching and larval motility of gastrointestinal nematode parasites, especially in small ruminants. Condensed tannins also bind to minerals (Al, Ca, Co, Cu, Fe, Mg, Mn, P, and Zn). Although studies with ruminants have been contradictory, it has been reported that because the CT-metal ion complex is stable over a wide pH range, CT may reduce the bioavailability of minerals. Methane mitigation by feeding CT might be the most impactful benefit for ruminant production. Many empirical equations have been developed to predict ruminal methane emissions, but very few have included CT. Future research should focus on the improvement of methodology to assess CT biological activity, interaction with other plant-specialized metabolites, and associated physiological and nutritional impacts on ruminants.

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

“…5), a large mixture of CTs with varying degrees of polymerization, PC and PD composition, and extent of branching. Include a third type of interflavan connectivity, such as the A-type linkage, and the possible number of distinct chemical entities in a six-subunit CT rises to 995,328 (Naumann et al, 2017). For example, the possible number of distinct chemical entities present in a CT with a length of six PC (catechin or epicatechin) or PD (gallocatechin or epigallocatechin) subunits connected by either a 4,8-or 4,6-B-type linkage is 131,072 (Naumann et al, 2017).…”

“…Thus, the take-home message from this section of the perspective is that CTs are typically formed in plants as an extremely diverse set of structures. Isolation of CTs from a natural source that contains a mixture of CT lengths from dimers to decamers (2-10 flavan-3-ol subunits) containing both PC and PD subunits and consisting of 4,8-, 4,6-B-type and A-type linkages theoretically may contain up to 22 billion distinct chemical entities (Naumann et al, 2017). Include a third type of interflavan connectivity, such as the A-type linkage, and the possible number of distinct chemical entities in a six-subunit CT rises to 995,328 (Naumann et al, 2017).…”

“…Thus, the take-home message from this section of the perspective is that CTs are typically formed in plants as an extremely diverse set of structures. For example, the possible number of distinct chemical entities present in a CT with a length of six PC (catechin or epicatechin) or PD (gallocatechin or epigallocatechin) subunits connected by either a 4,8-or 4,6-B-type linkage is 131,072 (Naumann et al, 2017). Include a third type of interflavan connectivity, such as the A-type linkage, and the possible number of distinct chemical entities in a six-subunit CT rises to 995,328 (Naumann et al, 2017).…”

“…For example, the possible number of distinct chemical entities present in a CT with a length of six PC (catechin or epicatechin) or PD (gallocatechin or epigallocatechin) subunits connected by either a 4,8-or 4,6-B-type linkage is 131,072 (Naumann et al, 2017). Include a third type of interflavan connectivity, such as the A-type linkage, and the possible number of distinct chemical entities in a six-subunit CT rises to 995,328 (Naumann et al, 2017). Isolation of CTs from a natural source that contains a mixture of CT lengths from dimers to decamers (2-10 flavan-3-ol subunits) containing both PC and PD subunits and consisting of 4,8-, 4,6-B-type and A-type linkages theoretically may contain up to 22 billion distinct chemical entities (Naumann et al, 2017).…”

“…Include a third type of interflavan connectivity, such as the A-type linkage, and the possible number of distinct chemical entities in a six-subunit CT rises to 995,328 (Naumann et al, 2017). Isolation of CTs from a natural source that contains a mixture of CT lengths from dimers to decamers (2-10 flavan-3-ol subunits) containing both PC and PD subunits and consisting of 4,8-, 4,6-B-type and A-type linkages theoretically may contain up to 22 billion distinct chemical entities (Naumann et al, 2017). With the exception of the few very low-molecular-weight CTs that are commercially available or can be readily isolated in relatively pure form, samples arising from purification of plant materials contain a plethoric mixture of CT compounds, which cannot currently be separated into individual compounds and are characterized and used as a mixture in subsequent studies.…”