CONDENSED TANNINS DETER FEEDING BY BROWSING RUMINANTS IN A SOUTH-AFRICAN SAVANNA

The palatability of 14 species of woody plant was assessed for these species of browsing ruminant, namely kudus, impalas and goats. Results show that palatability was most clearly related to leaf contents of condensed tannins. The effect was a threshold one, with all plants containing more than 5% condensed tannins being rejected as food during the wet season period. In contrast palatability was not influenced by concentrations of protein-precipitating polyphenols, and only weekly related to contents of nitrogen, phosphorus, cations, fibre components and other secondary metabolites. Insect herbivory shows a different pattern. These findings support the hypotheses that (i) condensed tannins function to protect plant cell walls against microbial attack; (ii) hydrolyzable tannins function to inactivate the digestive enzymes of insect herbivores. Large mammmalian herbivores are influenced by condensed tannins due to their dependence upon microbial fermentation of plant cell walls for part of their energy needs.