The Impact of Perennial Ryegrass Variety Throughout the Growing Season on in vitro Rumen Methane Output
The selection and feeding of perennial ryegrass varieties may affect enteric methane (CH4) output due to changes in rumen fermentation dynamics as a result of differences in herbage chemical composition. Thus, the objective of this study was to determine the effects of perennial ryegrass variety (PRV) harvested throughout the growing season on herbage chemical composition and on in vitro rumen fermentation variables and CH4 output. Seven PRV (Alto, Arrow, Bealey, Dunluce, Greengold, Malone, Tyrella), managed under a simulated grazing regime, were incubated in a batch culture for 24 h with rumen fluid and buffer. PRV had no effect (P > 0.05; SEM 0.41) on CH4 output per gram of DM incubated (CH4i; mean values for Alto, Arrow, Bealey, Dunluce, Greengold, Malone, Tyrella were 23.9, 24.0, 24.7, 25.3, 25.2, 24.2 and 24.7 (SEM 0.41) ml CH4 g−1 DM incubated, respectively). Although PRV had an effect (P < 0.001; SEM 1.3) on total gas production per gram of DM incubated, the scale of the effect was small (range of mean values among PRV was 148–160 ml), and PRV had no effect (P > 0.05) on apparent DM disappearance during the in vitro rumen incubation. Thus, the lack of an effect of PRV on CH4i reflected the small scale or lack of effects on herbage composition and in vitro rumen fermentation variables. Hence, these results provide no encouragement that choices among the PRV examined, produced within the management regimes operated, would reduce enteric methane production.
KeywordsVolatile Fatty Acid Rumen Fluid Water Soluble Carbohydrate Rumen Fermentation Organic Matter Digestibility
Funding for this study was provided by the Department of Agriculture, Fisheries and Food (RSF No. 07 517). The authors thank Jim Grant, Séan Lynch, and Grange Laboratories staff.
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