In vitro rumen methane output of perennial ryegrass varieties and perennial grass species harvested throughout the growing season.

摘要

The selection and feeding of perennial ryegrass (Lolium perenne L.) varieties (PRV) or perennial grass species (PGS) may affect enteric methane (CH₄) output because of changes in the fermentation dynamics in the rumen as a result of differences in herbage chemical composition. The objective of this study was to determine the effects of PRV and PGS harvested throughout the growing season on herbage chemical composition, and in vitro rumen fermentation variables and CH₄ output per unit of feed using a batch culture technique. Seven PRV (Experiment 1: Alto, Arrow, Bealey, Dunluce, Greengold, Malone, Tyrella) and six perennial grasses [Experiment 2: perennial ryegrass (Navan), perennial ryegrass (Portstewart), cocksfoot, meadow fescue, tall fescue, timothy; defined as PGS], managed under a simulated grazing regime, were incubated for 24 h with buffered rumen fluid in two separate experiments. The CH₄ output per unit of feed dry-matter (DM) incubated was not affected (P4 output per unit feed DM disappearing during the in vitro rumen incubation was not affected by PRV (33.9-35.1 (SEM 0.70) mL g-1 DM), and although there was an overall PGS effect (P<0.05; 37.2-40.3 (SEM 0.71) mL g-1 DM), none of the paired contrasts between PGS were significant when analysed using Tukey adjusted comparisons. This outcome reflected either small-scale or a lack of treatment effects on individual herbage chemical composition (e.g. 454-483 g NDF kg-1 DM, 215-224 g CP kg-1 DM and 94-122 g water-soluble carbohydrate (WSC) kg-1 DM across PRV; 452-506 g NDF kg-1 DM, 208-243 g CP kg-1 DM and 73-131 g WSC kg-1 DM across PGS) and in vitro rumen fermentation variables. Hence, these results provide no encouragement that choices among the grasses examined, produced within the management regimes operated, would reduce enteric CH₄ output per unit of feed in vivo. However, the technique utilized did not take account of animal x PRV or PGS interactions, such as potential differences in intake between animals, that may occur under farm conditions.