Results of a screening programme to identify plants or plant extracts that inhibit ruminal protein degradation

One aim of the EC Framework V project, 'Rumen-up' (QLK5-CT-2001-00-992), was to find plants or plant extracts that would inhibit the nutritionally wasteful degradation of protein in the rumen. A total of 500 samples were screened in vitro using C-14-labelled casein in a 30-min incubation with ruminal digesta. Eight were selected for further investigation using a batch fermentation system and soya protein and bovine serum albumin as proteolysis substrates; proteolysis was monitored over 12 h by the disappearance of soluble protein and the production of branched SCFA and NH3. Freeze-dried, ground foliage of Pelliphyllum peltatum, Helianthemum canum, Arbutus unedo, Arctostaphylos uva-ursi and Knautia arvensis inhibited proteolysis (P<0 center dot 05), while Daucus carota, Clematis vitalba and Erica arborea had little effect. Inhibition by the first four samples appeared to be caused by the formation of insoluble tannin-protein complexes. The samples were rich in phenolics and inhibition was reversed by polyethyleneglycol. In contrast, K. arvensis contained low concentrations of phenolics and no tannins, had no effect in the 30-min assay, yet inhibited the degradation rate of soluble protein (by 14%, P<0 center dot 0001) and the production of branched SCFA (by 17 %, P < 0 center dot 05) without precipitating protein in the 12-h batch fermentation. The effects showed some resemblance to those obtained in parallel incubations containing 3 mu M-monensin, suggesting that K. arvensis may be a plant-derived feed additive that can suppress growth and activity of key proteolytic ruminal micro-organisms in a manner similar to that already well known for monensin.