In vitro fermentative traits of Australian woody perennial plant species that may be considered as potential sources of feed for grazing ruminants

A range of Australian woody perennial plant species (n = 128 samples) were screened in vitro for overall fermentability and the capacity to induce favourable metabolic pathways in the rumen. Plants were tested in a batch rumen culture system, where gas pressure, pH and total volatile fatty acids were used as indicators of overall plant fermentability, and concentrations of methane, ammonia, acetate and propionate indicated changes in fermentation end products. In vitro fermentation of 52 of the plants yielded a gas pressure that was similar to, or higher than, the positive control (i.e., oaten chaff). Five plants produced less methane (mL/g dry matter supplied) without reducing total gas production, 54 reduced both methane and gas production, 47 reduced neither, and 22 reduced gas production but not methane production. All plants produced relatively low amounts of ammonia, while only 22 reduced the acetate: propionate ratio. Variability in response occurred at the genus and species level and plants with some favourable fermentative traits were identified. The screening of Australian woody perennial plants not previously considered for grazing systems illustrated the possibility of using some species to manipulate rumen fermentation, either as part of a mixed diet or to identify plant compounds associated with bioactivity in the rumen.