In vitro screening of temperate grasses, legumes, and herbs for anti-methanogenic potential and fermentation profile for Australian dairy systems

Context Grazing-based dairy systems in Australia are a major source of enteric methane production that contributes to global greenhouse-gas emissions. Enhancing pasture quality and incorporating lower methane yielding pasture species into ruminant production systems are dietary manipulation strategies for methane mitigation. Aims Samples of 12 temperate pasture species collected during spring and autumn in medium- and high-rainfall temperate dairy grazing systems in Victoria, Australia, were screened for their antimethanogenic potential and fermentation profiles during spring and autumn in medium- and high-rainfall temperate dairy grazing systems in Victoria, Australia. Methods Pasture species (four grasses, four legumes and four herbs) were harvested at a grazing-ready, vegetative, growth stage from farms in the region of either Ellinbank or Hamilton, VIC, Australia, and oven dried at 60°C for 72 h. Ground samples were analysed for their nutritive characteristics and in vitro fermentation characteristics, including methane, volatile fatty acid and ammonia nitrogen production. Key results Fermentation of legumes resulted in higher total volatile fatty acid concentrations, ammonia nitrogen production and methane production across seasons than did fermentation of grasses and herbs (P < 0.01). The herbs burnet (Sanguisorba minor) and yarrow (Achillea millefolium) reduced methane production by 40 to 50% and methane as a proportion of total gas by 20 to 35%, across seasons, compared with perennial ryegrass (Lolium perenne L.). Similarly, burnet and yarrow had the lowest total volatile fatty acid production across both seasons (78.80 and 78.05 mM respectively; P < 0.001). Principal component analysis showed a positive relationship between methane and total gas production and total volatile fatty acids, and a negative relationship with fibre fractions. Conclusions Both burnet and yarrow were identified as promising species for enteric methane mitigation, likely owing to their plant secondary compound profiles. Implications Burnet and yarrow are currently uncommon in temperate dairy systems in Australia; however, on the basis of these findings, they should be investigated further for their promising methane mitigation properties. If results can be confirmed in vivo, combining burnet and yarrow into Australian temperate pasture systems would be a cost-effective strategy that farmers could adopt to work towards industry greenhouse-gas reduction targets.