BINDING OF POLY(ETHYLENE GLYCOL) TO SAMPLES OF FORAGE PLANTS AS AN ASSAY OF TANNINS AND THEIR NEGATIVE EFFECTS ON RUMINALL DEGRADATION

A procedure to measure poly(ethylene glycol) (PEG) binding to plant sa mples is described. The amount of PEG bound to a sample was found to b e reproducible with a small coefficient of variation (0.5%). The PEG-b inding capacity of plant samples was not affected by predrying of the samples at 90 degrees C, unlike the colorimetric methods for determina tion of tannins. Both the PEG-binding and the protein precipitation ca pacity of the plant samples were found to be useful in predicting the negative effects of tannins on ruminal degradation of the plant materi al. However, PEG binding to plant samples had an advantage over protei n precipitation in samples in which formation of strong tannin-protein complexes results in low extractability of tannins. For this reason, the binding method was found to be preferable to the protein precipita tion method in predicting the negative effect of tannins on ruminal de gradation of forage plants.