By means of the representative scientific publications review on the tannins biochemistry, the main results related to their beneficial and antinutritional properties from chemistry-analytical, in vitro and in vivo studies were presented. The paragraphs are greater relevance and the repercussion of the knowledge acquired on these compounds is described; in the development of viable strategies of feeding. Historically, until the chemistry of natural products was not developed quantitatively, the animal nutrition studies with phenolic forages sources were insufficient. The first tests made after 1950, were directed to the phytochemical characterization of the majority tannin sources and the determination of the biological activity of the main groups, with particular emphasis in fodder leguminous like additional resource of nutrients. In one second stage the analytical techniques were implemented and validated that would be used to describe the polyphenols antifeeding effect and its interaction with the primary and secondary metabolites. The critic concentrations, in which these compounds could affect the good digestive process of ruminants and monogastric were postulated. Besides, the detrimental action of tannins hydrolysables and condensed in different conditions of feeding was compared, determining the variables of greater influence in the toxicological action. Independently to that the investigations made until the present have contributed much information as far as the characteristics of vegetal tannins, at the present time exists important subjects such as, the mechanisms related to the antihelmintic effect, the ecological function of hydrolysables tannins in non leguminous species and the interaction of polyphenols with alkaloids; among others, that have not been boarded with force; reason why integral studies need to explain these urgent questions.
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