Abstract. Plant material from Rheum palmatum (root) and Frangula alnus (bark) were tested to
study their effects as feed additives to decrease methane production from ruminal fermentation of a
forage-based diet, using a rumen simulating fermenter (RUSITEC). Sixteen fermentation units
(vessels) were set up for the experiment that lasted 19 days. Each vessel was fed 16 g of a mixed
substrate consisting of 800 g/kg forage and 200 g/kg concentrate. Treatments were assigned to the
experimental units (vessels) according to a completely random design. Treatment vessels were
supplied with either milled root from R. palmatum or milled bark from F. alnus (four vessels per
plant species) added at 1 g/day (62.5 mg additive/g substrate or 1.66 g/l in the fermenter). Another
four vessels received 12 AM of monensin (positive control) added to the basal diet, and the remaining
four vessels were controls (no additive). Monensin induced changes that were coincident with those
usually reported in the literature. R. palmatum caused a significant decrease in methane production,
associated with changes in the VFA production pattern. F. alnus altered slightly fermentation
parameters. D 2006 Published by Elsevier B.V.