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

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 (P >0 AE05) by PRV (range of mean values across PRV of 23AE9–25AE3 (SEM 0AE41) mL g )1 DM) or by PGS (25AE6–26AE6 (SEM 0AE37) mL g )1 DM). The CH4 output per unit feed DM disappearing during the in vitro rumen incubation was not affected by PRV (33AE9–35AE1 (SEM 0AE70) mL g )1 DM), and although there was an overall PGS effect (P <0 AE05; 37AE2–40AE3 (SEM 0AE71) mL g )1 DM), none of the paired contrasts between PGS were significant when analysed using Tukey adjusted comparisons. This outcome reflected either