Methane from ruminant livestock
Livestock farming is responsible for 8-10% of the world’s greenhouse gas emissions. Methane produced by ruminants (animals with a four-part stomach, including cattle and sheep) us a major contributor to the problem.
Ruminant animals play a major role in human food production, converting non-human edible plant material to high-quality products such as milk and meat.The challenge for research is to find practical ways to mitigate methane production, without compromising ruminants’ role in converting on-food crops to human food.
Methane production from ruminants is a natural and inevitable outcome of rumen fermentation - the process through which non-human edible plants such as grass is converted into products such as milk and meat.
Scientists have tried to reduce methane emissions from ruminants as doing so would allow the animals to retain more energy and produce meat and milk more efficiently. However, success has so far been limited as microbes in the rumens’ stomachs adapt quickly to intervention.
Climate change has increased the urgency to tackle the problem. A Global Research Alliance on Agricultural Greenhouse Gases has been formed by more than 30 countries to coordinate international efforts to mitigate greenhouse gas emissions from agriculture. Its scientific objectives are to measure and report national greenhouse has emissions, to understand the biology and management practices that influence emissions from agriculture and to explore methods for the direct reduction of those emissions. The policy objectives are to find ways to lessen the impact of agriculture on climate change.
The most effective way found so far to lower methane emissions from animal production is to identify management practices that avoid production inefficiencies. Avoiding keeping animals that produce little to long periods - such as beef cattle with low growth-rates - and increasing general rates of production efficiencies in other are some practices that help. Enormous efforts are being made across the world to find methods that are effective, safe and sustainable. Nutrition has played an important role here. High grain diets cause ruminants to produce less methane per unit of intake, however the carbon footprint of producing grain needs to be taken into account in assessing any overall benefit to greenhouse gas emissions. Consideration also needs to be given to the important role of grasslands in carbon sequestration, which can offset part of the damaging effect of methane emissions. Animal genetics is also likely to play a role, as recent research suggests some animals produce less methane than others - possibly because they have different microbes in their rumens. A vaccine against archea (microorganisms which form methane) holds promise, but the science is a long way off from being used on farms. There is also interest in developing feed additives that will inhibit methane production.
Recent research has generally been based on two approaches. the most common is empirical, where plant materials and industrial co-products have been screened for their effects on reducing methane production. Materials such as garlic oil, cashew shell oil and other essential oils have been found to be effective in reducing methane production. General acceptance of any of these has yet to be achieved, however.
An alternative approach is to combine genetics with drugs. Some genomes of ruminal methanogens (methane-producing microorganisms) have been sequenced and key genes from those genomes are being identified. This may enable the design of specific inhibitors.
The problem is that too little is known about the microorganisms that form methane in the rumen of livestock, particularly with the types of diets used in the UK. It is usually assumed that these archea will be the same as found in New Zealand, Australia or North America. Projects are now under way to describe the archaeal communities in UK cattle and sheep. The next stage of research will be to understand whether archaeal communities of differing composition produce different quantities of methane.
It is difficult to predict the outcome of all these areas of research but the challenge of mitigating methane emissions from ruminants remains a key one for the livestock research community.
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