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Condensed Tannins and Ruminant Nutrition

B. R.Min1, S. P. Hart1, and T. N.Barry2

1E (Kika) de la Garza Institute for Goat Research, Langston University, OK, 2Massey University, Palmerston North, New Zealand

The objective of this paper is to present a brief overview of effects of condensed tannins (CT) on ruminant nutrition and animal production. Tannins are phenolic plant secondary compounds and are widely distributed in the plant kingdom. Tannins exist primarily in CT and hydrolyzable tannin (HT) forms. HT are potentially toxic to ruminants. Pyrogallol, a hepatotoxin and nephrotoxin, is a product of HT degradation by ruminal microbes. However, CT are considered to be non (or less)-toxic because they are not absorbed from the intestine. CT are the most common type of tannin found in temperate legumes, trees, and shrubs. CT often precipitate with dietary proteins at pH 5.5-7.0, with the extent of this reaction being dependent on the concentration, molecular weight, and structures of the CT and of the protein. Low concentrations of CT (2-4% CT, DM basis) in several temperate plant species (e.g., Lotus corniculatus, sulla, and sainfoin) are beneficial for ruminants, and have resulted in improved milk yield, wool growth, live weight gain, ovulation, and lambing percentage, as well as preventing pasture bloat and reducing intestinal parasite burden. This is related to the reduced protein solubility and degradation in the rumen and to enhanced flow of non-ammonia nitrogen to the abomasum and to increased absorption of essential amino acids from the small intestine. However, high forage CT concentrations (5-10% CT) reduce voluntary feed intake and digestibilities, especially in tropical regions where feed choices and quality are limited. At present, there are few opportunities for reducing the negative effects of high CT concentrations in these regions and future progress for improving ruminant productivity is dependent on improving our understanding of the chemical structure of CT from various plants and understanding how CT affect ruminal microbes and forage nutritive value.


 

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