In vitro fermentation patterns and methane production as influenced by cultivar and season of harvest of Lolium perenne L.

In some European countries, the majority of annual enteric methane (CH4) emissions by ruminants occur at pasture - a direct result of the predominance of grazing within ruminant production systems. However, there are only limited data available as to the effect of perennial ryegrass cultivar and season of harvest on CH4 production. Using the in vitro gas production technique, the effect of perennial ryegrass cultivar on fermentation characteristics and CH4 production was determined (Experiment 1) and the persistence of these traits throughout the growing season for two cultivars, identified from Experiment 1 as having either a high or low methanogenic potential, was examined (Experiment 2). In Experiment 1, organic matter (OM) digestibility and cumulative total gas production profiles were unaffected by cultivar but, with regard to the kinetics of CH4 production, the asymptote value (A), cumulative CH4 yield at 72 h, and the fractional rate (p) of CH4 production at both time of 0(.)5A (T-2/(1)) (mu CH4T2/(1)) and at 48 h (mu CH(4)48h) were significantly (P < 0(.)05) different. The amount of digested OM, as a proportion of cumulative CH4 production (DigOM/CH4) at 24 and 72 h after commencement of inoculation, revealed that the amount Of Substrate required to produce 1 ml of CH4 also differed significantly between cultivars (P < 0(.)01). In Experiment 2, regrowth number significantly modified the majority of measured samples (P < 0(.)01); cultivar effects were limited to the lag phase of the Cumulative CH4 production curve and DigOM/CH4 at 8 h only (P < 0(.)05). These results suggest that differences exist between cultivars in how OM is partitioned following microbial fermentation and that these differences demonstrate persistency throughout the growing season. in the course of time it may be possible to exploit these differences through cultivar selection and plant breeding programmes, and thereby reduce enteric CH4 emissions within pastoral production systems.