Tannin content of selected legume species

Multipurpose trees and bushes are used as supplementary feeds to augment low quality diets in goats. The leaves and pods are rich in proteins, minerals, and vitamins, hence they serve as alternatives to expensive concentrates. However, some tree legumes contain secondary compounds, which are toxic when consumed ad libitum. Tannin is one of the many types of secondary compounds found in plants. It is a bitter plant substance that has been identified as a major constraint in the utilization of plant species by livestock. According to agricultural studies, tannins bind with nutritional components in the digestive tract and to the wall of the digestive tract itself, producing negative effects on intake and digestibility and limiting their intensive use in livestock feeding. However, tannins may also have biological effects that may aid in the control of gastrointestinal parasites. There are many different types of tannins, but condensed tannins (CT) are the most common types of tannins found in forage legumes, trees, and shrubs. Orden et al (CLSU) [Central Luzon State University, Maligaya, Science City of Muñoz, Nueva Ecija, Philippines] evaluated the tannin content of 11 tree legume species grown in the Small Ruminant Center at CLSU from Oct 2005 - Sept 2007. The study highlighted the phenolic concentrations and different condensed tannin fractions of the different legumes used as feeds to goats. Phenolic compounds or the chemical substances in plants were analyzed using Folin Ciocalteu. These are expressed as either total extractable phenolics (TEPH) or total extractable tannin (TET). TEPH or the tannic acid equivalent (TAE) of the selected legume species ranged from 1.71% to 12.28% DM and TET from 0.16% - 8.27% DM. Of the 11 tree legume species, Flemingia had the highest TEPH value of 12.28% followed by Leucaena, 11.86% and Desmanthus, 8.9%. The rest had 8%. It was noted that more than 65% of the extractable phenolic compounds in Flemingia and Leucaena were accounted as TET. This corroborated other studies that showed that TAE of these legumes was higher than the 5.57% of the species of tree/shrubs commonly used as ruminant feed in Batangas [Philippines]. This could be a potential factor that affected nitrogen degradation in the rumen and possibly protein availability in the lower gut. Fractionation of the total condensed tannin showed that among the 11 species of legumes that were analyzed. Flemingia macrophylla and Leucaena leucocephala had all the CT fractions, namely, delphinidin, cyanadin, and pelargonidin. Other legumes such as Desmanthus virgatus, Arachis pintoi, and Centrosema pubescens showed high prevalence of delphinidin and cyanodin only and the rest of the legumes were found to have no CT. Results indicated that total condensed tannins (TCT) were high in Flemingia macrophylla (4698.94 micro ug/g DM) followed by Leucaena leucocephala (2826.45 micro u g/g DM), Arachis pintoi (1817.42 micro g/g DM), and Desmanthus virgatus (1176.40.42 micro g/g DM). Results showed that Flemingia and Leucaena were found to have higher polyphenolic compounds in the form of TEPH, TET, and TCT. These are promising legumes species for goats as these are known to have anthelmintic properties. However, further study is recommended to determine the direct effect of polyphenolic compounds in reducing internal parasites in goats.