The objective of this study was to examine the effects of water-soluble carbohydrate (WSC) concentration and type on the in vitro rumen methane (CH4) output of perennial ryegrass (PR) using a 24-hour batch-culture gas production technique. Dried and milled PR was incubated either alone (PR-O) or with added sucrose (PR-S), inulin (PR-I), or sucrose plus inulin (PR-S+I; sucrose:inulin ratio of 1:4) in sealed glass bottles [0.5 g total substrate dry matter (DM) per bottle] at 39 °C for 24 hours with buffered rumen fluid. The WSC types were added (except for PR-O) so that the WSC concentration in each fermentation bottle at the start of the incubation was either 180 (i.e., PR-O), 225, 270, 315, or 360 g/kg of total substrate DM incubated. There were linear decreases in CH4 output per gram of DM disappeared (CH4/ivDMD) and per mmol of total volatile fatty acid output (CH4/tVFA) with increasing WSC concentration in the incubated substrate. The WSC type had no effect on in vitro rumen CH4 output. It is concluded that since CH4/ivDMD and CH4/tVFA were reduced by increasing the concentration of WSC incubated with PR, it would be worthwhile to undertake in vivo experiments to examine these effects on in vivo CH4 emissions per unit of animal product.peer-reviewedFunding for this study was provided under the National Development Plan through the Research Stimulus Fund administered by the Department of Agriculture, Food & the Marine (RSF no. 07 517).Department of Agriculture, Food and the Marin
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