Harnessing plant bioactivity for enteric methane mitigation in Australia

Abstract

This review provides examples of the utilisation of plant bioactivity to mitigate enteric methane (CH 4 ) emissions from the Australian ruminant production systems. Potential plant-based mitigation strategies that reduce CH 4 without major impacts on forage digestibility include the following: (i) low methanogenic tropical and temperate grass, legume and shrub forage species, which offer renewable and sustainable solutions and are easy to adopt, but may have restricted geographical distribution or relatively high costs of establishment and maintenance; (ii) plant-based agricultural by-products including grape marc, olive leaves and fruit, and distiller's grains that can mitigate CH 4 and provide relatively cheap high-nutrient supplements, while offsetting the impact of agricultural waste, but their use may be limited due to unfavourable characteristics such as high protein and water content or cost of transport; (iii) plant extracts, essential oils and pure compounds that are abundant in Australian flora and offer exciting opportunities on the basis of in vitro findings, but require verification in ruminant production systems. The greatest CH 4 mitigation potential based on in vitro assays come from the Australian shrubs Eremophila species, Jasminum didymium and Lotus australis (>80% CH 4 reduction), tropical forages Desmanthus leptophyllus, Hetropogon contortus and Leucaena leucocephala (~40% CH 4 reduction), temperate forages Biserrula pelecinus (70-90% CH 4 reduction), perennial ryegrass and white clover (~20% CH 4 reduction), and plant extracts or essential oils from Melaleuca ericifolia, B. pelecinus and Leptospermum petersonii (up to 80% CH 4 reduction). Further research is required to confirm effectiveness of these plant-based strategies in vivo, determine optimal doses, practical modes of delivery to livestock, analyse benefit-cost ratios and develop pathways to adoption.

Perspective: science and the future of livestock industries

“…At that time, our thinking was constrained by three pre-conceptions: (a) methane production in the rumen was essential for taking up hydrogen ions and preventing acidosis, so blocking the process would kill the animal; (b) methane production was not a heritable trait; (c) feed additives could not reduce methane synthesis. The period 2006–2014 saw major advances in methane science, and all three pre-conceptions were rejected – we now have estimates of heritability ( 30 , 31 ) and a variety of novel forages and dietary additives that can reduce emissions [review: ( 32 )]. Moreover, blocking methane synthesis is not detrimental for the animal ( 33 ) – in fact, it improves animal efficiency because carbon that would have escaped by eructation is redirected into production ( 34 ).…”

Reducing enteric methane of ruminants in Australian grazing systems – a review of the role for temperate legumes and herbs

“…Moreover, while the methanogenic potential of subterranean clover is variable (Table 1), it is also heritable so it can be manipulated by plant breeding (Kaur et al . 2017; Durmic et al . 2022).…”

“…Understanding how these factors affect CH 4 reductions is essential in being able to predict the potential CH 4 reductions associated with the introduction of a species into a system. Also, any potential animal and human health implications of PSC need to be fully understood (Durmic et al . 2022).…”

“…Of the other mainstream pasture species, subterranean clover is of interest because it is the most widely sown annual legume in Australia at 29.3 million ha (Nichols et al 2012), and when fed to sheep has been found to reduce CH 4 production by 30% compared with feeding ryegrass (Muir et al 2020). Moreover, while the methanogenic potential of subterranean clover is variable (Table 1), it is also heritable so it can be manipulated by plant breeding (Kaur et al 2017;Durmic et al 2022). The other plant traits that contribute to the current success of subterranean clover include its prostate growth making it tolerant to grazing, its ability to bury burrs and protect seed from grazing, a diversity of flowering times to enable it to be grown in many different environments (250-1200 mm of rainfall) and being productive in mixtures (Nichols et al 2013).…”

A regional-scale assessment of nutritional-system strategies for abatement of enteric methane from grazing livestock

“…No matter what grazing-based production system is in use, there is scope to change not only the general nutritional value of the forage, but to introduce specific CH 4 -suppressing forages. More than 200 000 plant secondary compounds, or phytochemicals, have been identified (Hartmann 2007), and some have anti-methanogenic proprieties, including tannins, essential oils, and saponins (Durmic et al 2022). In many cases, these may possess anti-nutritional characteristics, and so the aim is to find the equilibrium between the beneficial CH 4 abatement and the optimum nutrient utilisation.…”