In the tropics, animal production is compromised by the lack of suitable forage. As a further constraint, low-fertility, acid soils are prevalent in areas where many small and medium size farmers are dependent upon livestock agriculture as their main source of income. This prevents the incorporation of high-quality forage legumes into those grazing systems, as these legumes do not perform very well under those conditions. In turn, most tropical forage legumes with good adaptation to acidic soils are of low quality and poor acceptability by livestock, which might be associated with their high contents of condensed tannins. However, research on the impact of condensed tannins upon the nutritional value of forage has not provided unequivocal results. This could be related to the variation in structure (molecular weight and monomeric composition) observed among condensed tannins from different legumes. This study investigated the impact of condensed tannins from different tropical legumes on the degradation of different substrates by rumen microorganisms and/or their enzymes under the scope of structure-activity relationships.
It was concluded that whereas condensed tannins in tropical legume could act as anti-nutritive factors, their nutritional impact is a function of their concentration in plant tissue, their association with plant tissue (i.e soluble or associated) and their structure. In addition, condensed tannin structure varies considerably according to plant species and in response to different environmental factors.
Rosales, R.B. Condensed tannins in tropical forage legumes: their characterisation and study of their nutritional impact from the standpoint of structure-activity relationships [PhD thesis]. (2000) 400 pp. [PhD Thesis, University of Reading]