Effects and fate of tannins in ruminant animals, adaptation to tannins, and strategies to overcome detrimental effects of feeding tannin-rich feeds

Trees and shrub foliage and agro-industrial by-products are of importance in animal production because they do not compete with human food and can provide significant protein supplements, especially in the dry season. But, these feed resources are generally rich in antinutritional factors, particularly tannins. The amount of tannins that they contain vary widely and largely unpredictably, and their effects on animals range from beneficial to toxicity and death. With a better understanding of tannin properties, effects and fate; and with proper management they could become invaluable sources of protein for strategic supplementation. The effects and fate of tannins in the rumen, and post-absorption, and likely mechanisms of adaptation to tannins are discussed. Simple methods based on post-harvest technology, treatment with low-cost chemicals, biological treatments, and supplementation with tannin-complexing agents, to enhance the feeding value of tannin-containing feeds; and roles of rumen microbes in degradation and overcoming the detrimental effects of tannins are also presented. (C) 2003 Published by Elsevier Science B.V.