Polyphenolics are a common group of anti-nutritional factors, which occur in many browse plants found in the tropics. They have been implicated in the poor performance of ruminants. Detrimental effects could occur in the rumen or, if phenolics or their metabolites escape degradation, in the intestines or animal tissues. Most published reports have concentrated on examining the effect of feeding plant material containing anti-nutritional factors or the effects of administration of plant extracts containing a mixture of possible anti-nutritional compounds. We have adopted an alternative approach by investigating the metabolism of individual phenolic compounds rather than broad groups. For our initial studies the flavonol glycoside rutin (a monomeric unit of many condensed tannins) and gallic acid (monomeric unit of many hydrolysable tannins) were chosen as models to study the fate of these compounds in the rumen environment.

All samples were analysed for phenolics by HPLC (Spectra Physics Focus System) using a diode-array detector (220-900nm) and a 250 × 4mm column packed with ODS Hypersil, CIS. Samples run on this system were eluted with a linear gradient of 2% glacial acetic acid(A) and methanol(B), 100% A - 100% B in 30-60 min, the gradient run time depending on the type of sample being analysed. Sample peaks were identified using their retention time, maximum absorbances and peak spectra relative to known phenolic standards. All samples containing phenolics were extracted in 100% methanol by homogenization (Polytron AG Kinematic, Switzerland) at 13,500 rpm for 2 × 90 sec. The homogenate was then centrifuged at 1·000g for 10 min. The resulting supernatant was analysed for phenolics by HPLC.