|NAUMANN, HARLEY - UNIVERSITY OF MISSOURI|
|TEDESCHI, LUIS - TEXAS A&M UNIVERSITY|
|HUNTLEY, NICHOLE - IOWA STATE UNIVERSITY|
Submitted to: Brazilian Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2017
Publication Date: 12/1/2017
Citation: Naumann, H.D., Tedeschi, L.O., Zeller, W.E., Huntley, N.F. 2017. The role of condensed tannins in animal production: advances, limitations and future directions. Brazilian Journal of Animal Science. 46:929-949.
Interpretive Summary: Tannins are a class of plant components present in a variety of forages and other plants. They have been shown to have an impact on livestock health and productivity. These effects are tied to the tannins’ ability to bind to protein. 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 tannins and the condensed tannins. This article reviews recent advances in our knowledge of the interactions of condensed tannins in the rumen, the limitations associated with understanding and using condensed tannins in ruminant animal production, and future needs for research to learn more of the role of condensed tannins in ruminant animal production. Special attention is given to condensed tannins’ biological activities in ruminant animals. These include anti-nutritional impacts of condensed tannins on ruminants and the ruminant animal’s protective mechanisms, condensed tannins’ binding to proteins and other nutrients, anti-parasitic activity of condensed tannins, and reduction of methane (a potent greenhouse gas) emissions. Future research should focus on the improvement of methodology to assess condensed tannin biological activity, interaction with other plant specialized metabolites, and associated physiological and nutritional impacts on the ruminant animal. Understanding the effects of condensed tannins on ruminant production will provide guidance on how to feed condensed tannin-containing forages and plant materials to ruminants to obtain optimal economic performance and minimize environmental impacts.
Technical Abstract: Tannins represent one of the most abundant polyphenolic compounds in plants, second only to lignin. 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 or condensed tannins. Hydrolysable tannins (HT) are esters of gallic or ellagic acid linked to a polyol core, typically glucose. Condensed tannins (CT) or proanthocyanidins (PA) 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. This paper describes 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 to optimize 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. However, ruminants can tolerate CT by slowly adapting the ruminal microbes to the toxic effects of CT and by releasing CT-binding salivary proteins to complex CT. The protein-binding ability of CT has some benefits to the ruminant. Proteins complexed by CT prevent their degradation in the rumen, subsequently releasing them in the lower gut for absorption by the animal. Recent data have suggested increased N retention when CT was fed 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. CT also bind to minerals (Al, Ca, Co, Cu, Fe, Mg, Mn, P, and Zn). Though 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 methane production by ruminants, but very few have included CT in the assessment. 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 the ruminant animal. Understanding the effects of CT on ruminant production will provide guidance on feeding of CT-containing forages and plant materials to ruminants to obtain optimal economic performance and minimize environmental impacts.