PLANT EXTRACTS AND THEIR POTENTIAL ROLE IN RUMINANT NUTRITION

摘要

The threat to human health associated with the use of antibiotic and chemical feed additives has prompted legislation in the EU to ban antimicrobial growth promoters (AGP), and has accelerated investigations into plants and their extracts as feed additives. The broad potential of plants and their extracts to replace AGP is illustrated by the progress of an EC Framework 5 project, 'Rumen-up' and its Framework 6 successor, 'REPLACE'. The Rumen-up project began with a targeted collection of 500 Europeanplants and their extracts, and partners tested their effects on ruminal proteolysis, protozoa, methanogenesis and lactate production. A success rate of about 5% in terms of positive hits illustrated that phytochemicals have great potential as 'natural'manipulators of rumen fermentation, to the potential benefit of the farmer and the environment. The REPLACE project has highlighted potentially useful plants in other species and in other aspects of ruminant production, particularly the control of intestinal pathogens and fatty acid biohydrogenation. Some of the positive samples had a benefit that could not be explained by our present knowledge of the effects of phytochemicals on ruminal microorganisms. For example, Knautia arvensis inhibited ruminal proteolysis by a novel mechanism that resembled that of monensin. Others exerted their effect via phytochemicals that are at least partially understood. Several plant extracts have been shown to inhibit methanogenesis, and several projects are exploring the potential of these extracts. Dietary essential oils cause decreased ruminal NH3 production, an effect that was shown /to be mediated partly by effects on ammonia-producting bacteria, on Prevotellaspp. and on the protein and starch fermenter, Ruminobacter amylophilus. Saponins-containing plants and their extracts suppress the bacteriolytic activity of rumen ciliate protozoa, thereby enhancing total microbial protein flow from the rumen. The effects of some saponins are transient, because they are hydrolysed by bacteria to their corresponding sapogenin aglycones, which are much less toxic to protozoa. The potential benefits of phytochemicals as feed additives are therefore high and largely unexplored.