In vitro gas production and rumen fermentation profile of fresh and ensiled genetically modified high–metabolizable energy ryegrass

The objective of this study was to evaluate a technology designed to generate high metabolizable energy (HME) perennial ryegrass (Lolium perenne) for its potential to enhance forage feeding value and its influence on the microbial fermentation profile in an in vitro rumen incubation. The HME technology was implemented in ryegrass by modifying genes involved in lipid biosynthesis and storage, leading to accumulation of lipid droplets in the leaf. Independent HME ryegrass lines with a range of elevated leaf lipid concentrations were analysed for changes in fatty acids (FA) and possible associated changes in the broader nutritional profile, including the gross energy yield which was found to increase by 6.8%. To investigate the effect of ensiling on the HME ryegrass, controlled environment-grown plant material was ensiled on a miniature scale. Differences in the nutritional composition of the ensiled material largely reflected those of their fresh counterparts. Incubation of both fresh and ensiled HME ryegrass in rumen fluid resulted in: (i) less biohydrogenation compared to the control; (ii) a significant reduction of butyrate; (iii) a 10-15% decrease in the methane (CH4) proportion of the total gas production. In this paper we discuss the potential use of HME ryegrass to enhancing forage feeding value and the potential environmental benefits to the pastoral agriculture industry.