Comparison of wild type, AR1 and AR37 endophyte infected perennial ryegrass on in vitro methanogenesis

Abstract

Perennial ryegrass (Lolium perenne) is a major pasture species grazed by cattle and sheep in the temperate regions of Australia. The principal aim our study was to examine effects of ryegrass endophytic fungi on in vitro ruminal methanogenesis. Samples of perennial ryegrass pasture infected with either wild-type endophyte or the novel endophytes, AR1 or AR37, were seasonally collected, over 3years. Samples were collected during spring, a period which usually coincides with low alkaloid concentrations, and in late summer–autumn, a period in which alkaloid concentrations generally peak. The pasture samples were freeze–dried, ground and measured for concentrations of lolitrem B, ergovaline, peramine and total epoxy janthitrems. Samples of freeze–dried ground pasture were incubated in triplicate for 48h in vitro in cow rumen fluid. Gas production was measured at 9, 24 and 48h post inoculation, the same time at which gas headspace was sampled for CH4 concentration. Culture pH and in vitro dry matter disappearance were measured at 48h. In ryegrass with wild-type endophyte, mean (±SD) concentrations (mg/kg DM) of lolitrem B were 0.02±0.041 in spring and 1.2±0.89 in summer–autumn while, for ergovaline, the respective concentrations were 0.1±0.04 and 0.5±0.26 and for peramine 6.8±2.27 and 12.5±2.78. For ryegrass infected with AR1, concentrations of peramine were 6.7±2.17 in spring and 12.7±2.97 in summer–autumn. For ryegrass infected with AR37, concentrations of total epoxy-janthitrems were 0.05±0.060 in spring and 10.8±5.89 in summer–autumn. Lolitrem B and ergovaline were not detected in samples of ryegrass infected with AR1 or AR37 endophytes. Peramine was not detected in ryegrass infected with AR37 endophyte and epoxy-janthitrems were not detected in ryegrass infected with wild-type or AR1 endophytes. Neither endophytic strain nor concentration of alkaloid had any effect on CH4 production expressed as ml/g DM. However, CH4 production expressed as ml/g digested DM was lower from samples collected in spring than from samples collected in summer-autumn (P=0.001). Endophyte strain and sampling period had minor effects on other indices of rumen fermentation. Compared to ryegrass infected with wild type endophyte, the novel endophyte strains AR1 and AR37 do not inhibit CH4 production in vitro, and are unlikely to have any useful role in CH4 abatement strategies.