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

摘要

We previously generated a high–metabolizable energy(HME) perennial ryegrass (Lolium perenne) bygenetically modifying the plant to increase the leaf lipidcontent. Although substantial progress has been madetoward characterizing physiological changes of HMEryegrass, very limited information exists for feedingvalue and its suitability for adoption into the pastoralsystem. In this study, independent HME ryegrass lineswith a range of elevated leaf lipid concentrations wereanalyzed for changes in fatty acids and possible associatedchanges in the broader nutritional profile, includingthe gross energy, which was found to increase by 6.8%.Because ryegrass is often ensiled and fermentation in therumen leads to biohydrogenation of fatty acids as wellas enteric methane production, we sought to investigatethese effects on HME ryegrass. This was achieved byperforming mini-scale silos and using an automated gasmeasurement system to incubate the material in rumenfluid in vitro for 24 h. Our study included treatmentscomprising 3 independent HME ryegrass genotypesand wild-type control materials prepared fresh and assilage, employing in total 5 incubation studies, usingrumen fluids collected from 4 nonlactating Jersey ×Holstein cows. At intervals during the incubation, theproduction of gases, volatile fatty acids, and the degreeof biohydrogenation were measured. Statistical dataanalysis indicated that differences in the nutritionalcompositions of the ensiled materials largely reflectedthose of their fresh counterparts. Incubation of bothfresh and ensiled HME ryegrass in rumen fluid resultedin: (1) a greater percentage of valuable unsaturatedfatty acids compared with the control; (2) a significantreduction of butyrate; and (3) a 10 to 15% decrease inthe methane proportion of the total gas production.We conclude that ensiling could be a convenient optionfor preserving HME as a locally produced high-valuesupplementary feed; however, large-scale applicationneeds to be investigated. In this paper we discuss thepotential use of HME ryegrass to enhancing foragefeeding value and the potential environmental benefitsto the pastoral agriculture industry.