A study was conducted to examine in vitro ruminal fermentation profiles and methane production of some alternative forage species (n = 10) in Australia. Extent of fermentation was assessed using an in vitro batch fermentation system, where total gas production, methane production, and concentrations in ruminal fluid of volatile fatty acids (VFA) and ammonia were measured. Forages varied in their fermentability, with highest total gas, methane, VFA and ammonia production recorded from selected samples of Brassica napus L. cv. Winfred. Lowest methane production (i.e. 30% less than that formed by the highest-producing one) was observed in Plantago lanceolata L. cv. Tonic and Cichorium intybus L. cv. Choice. Selected plants, including P. lanceolata L. cv. Tonic, Brassica rapa L. cv. Marco, Brassica napus L. cv. Hunter had reduced acetate : propionate ratio and/or ammonia concentration, along with relatively low methane production compared with other species tested, while overall fermentation was not affected. It was concluded that selected novel forages have some advantageous fermentability profiles in the rumen and, in particular, inhibit methane production. However, before these can be recommended as valuable supplementary feedstuffs for ruminants in Australia, further studies are needed to confirm these effects over a range of samples, conditions and in vivo.

Ruminants produce large amounts of the greenhouse gas, methane, which can be reduced by supplementing feed with products that contain anti-methanogenic compounds, such as the solid winemaking by-product, grape marc. The aim of this study was to exploit compositional differences in grape marc to better understand the roles of condensed tannin and fatty acids in altering methanogenesis in a ruminant system. Grape marc samples varying in tannin extractability, tannin size and subunit composition, and fatty acid or tannin concentrations were selected and incubated in rumen fluid using an in vitro batch fermentation approach with a concentrate-based control. Four distinct experiments were designed to investigate the effects on overall fermentation and methane production. Generally, fatty acid concentration in grape marc was associated with decreased total gas volumes and volatile fatty acid concentration, whereas increased condensed tannin concentration tended to decrease methane percentage. Smaller, extractable tannin was more effective at reducing methane production, without decreasing overall gas production. In conclusion, fatty acids and tannin concentration, and tannin structure in grape marc play a significant role in the anti-methanogenic effect of this by-product when studied in vitro. These results should be considered when developing strategies to reduce methane in ruminants by feeding grape marc.

The Australian red meat industry has set a goal to be carbon neutral by 2030. Reaching this goal will be a challenge and will involve targeting ways to increase carbon in the landscape, improve efficiency of production and reduce methane emissions from ruminants. There are a number of different options the industry can pursue to try and achieve its goal, including changing grazing management practices and land-use to changing the animal, what it eats and the microbial ecology in their rumen. No single one of these options will enable the red meat industry to become carbon neutral by 2030, it will take a combination of all of them to help meet the challenge. We have been using an in vitro batch fermentation system and a Rusitec system as a quick, relatively inexpensive, way to screen; plants that already exist in our grazing systems, novel plants, plant extracts and organic waste products from the horticultural industry, for their potential to improve the efficiency of fermentation and reduce methane production in the rumen. We have also used these systems to provide an initial clue about the mechanism of action at the level of the ruminal microorganisms. We have identified variation in these traits amongst the plants, plant extracts and horticultural waste products we have tested that could help develop systems that reduce the environmental footprint of ruminants in tropical production systems in Australia and in other parts of the world.