At the climate meeting (COP26) that is being held in Glasgow has reached an agreement, promoted by the European Union and the United States and signed by more than 100 countries, to reduce methane emissions by 30% by 2030.
This gas has a short half-life in the atmosphere (10-12 years), but exerts a powerful greenhouse effect (80 times greater than CO₂ in a period of 20 years). It is considered responsible for a quarter of current global warming.
Most of the methane generated by human activity comes from the use of fossil fuels (gas and oil), coal mines, agriculture and livestock and waste management (landfills).
Measures to reduce emissions produced by the use of fossil fuels and coal and by landfills are well defined and there is the necessary technology to implement them. However, the possibilities of reduction in agriculture, and more specifically in livestockThey are more complicated and generate more controversy in the population.
Estimates of the Intergovernmental Panel on Climate Change (IPPC) indicate that livestock activity can account for 14.5% of global greenhouse gas (GHG) emissions. Of these, about two thirds are produced by ruminants (cows, sheep, goats, buffalo, deer), mainly due to the methane generated in the fermentation of food in the rumen (enteric methane). These figures are lower in Spain, since in 2020 livestock accounted for 9.1% of total GHG, 6.9% corresponding to enteric methane emissions, the vast majority (95%) coming from ruminants.
Why is methane generated in the rumen?
The microorganisms in the rumen can degrade fibrous food that cannot be digested by other animals and in this process generate nutrients for the ruminant. Thus, ruminal fermentation allows ruminants to transform plants that cannot be used in human food or other animals into animal products of high nutritional value (meat and milk).
In this fermentation process, hydrogen is generated, which if accumulated in the rumen would seriously impair the degradative activity of microorganisms, so there are mechanisms to maintain low hydrogen concentrations.
One of these mechanisms is methane formation, a process in which ruminal methanogenic archaea use CO₂ and hydrogen to generate methane (CH₄) and water. Another mechanism is the saturation of fatty acids in the diet carried out by ruminal microorganisms, since the hydrogen generated in fermentation is also used in this process.
Strategies to reduce emissions from livestock
Enteric methane produced by a ruminant is positively related to the amount of feed eaten. For this reason, cattle generate more than small ruminants (sheep and goats) and for this reason they are usually “blamed” to a greater extent for their emissions.
1. Balanced diets
Diet is a very important factor. Ruminants fed only forages generate higher amounts of methane per kilo of feed ingested than those that receive feed. For this reason, ruminants in grazing or extensive farms emit more methane per kilogram of meat or milk produced than ruminants in intensive farms, where they tend to receive diets with a high percentage of feed.
However, ruminants cannot be fed with feed alone. This would cause digestive pathologies and would waste their ability to take advantage of plant resources not usable by other animals and to use pasture on land unsuitable for cultivation, which also act as carbon sinks.
Formulating diets with highly digestible forages and an adequate level of feed to maintain optimal ruminal fermentation is a useful strategy to reduce methane emissions.
2. Use of additives with antimethanogenic potential
His search has been the target of numerous investigations in recent years. Some of these additives are very effective in studies in vitro, but its effects on animals are not consistent or reduce the production and quality of meat and milk.
However, 3-nitroxypropanol (3NOP) is currently available, a synthetic molecule that reduces methane production without adversely affecting animal production. According a meta-analysis of different studies, the administration of 3NOP can reduce methane emissions by 39.0% in dairy cows and 22.2% in fattening calves.
The 3NOP is still being evaluated to authorize its use in the United States and the European Union, but it is already being used in other countries such as Chile and Brazil.
3. Use of algae
The inclusion in the diet of small amounts of some red algae of the genus Asparagopsis also seems to be effective in reducing methane emissions in cows and calves without reducing their production.
Although the development of industrial methods for the production, processing and storage of these algae under conditions that allow to maintain their antimethanogenic compounds is still necessary, the results available so far are promising.
4. Genetic selection
On the other hand, Spanish researchers estimate that the genetic selection of cows with low methane emissions could reduce the emissions of dairy cattle by 20% in ten years in our country. The combination of these strategies will undoubtedly reduce enteric methane emissions in the coming years.
5. Decrease in the number of ruminants
Would it really be effective to reduce the ruminant population or the consumption of meat and milk to reduce methane emissions?
If the number of ruminants were to be reduced, it would be logical to first reduce those with the highest emissions per unit of product obtained, that is, ruminants in grazing and extensive farms. In Spain, a large part of grazing ruminants are autochthonous breeds that represent a large genetic heritage, so this action would imply an irreparable loss of biodiversity.
In addition, grazing contributes greatly to the conservation of natural spaces, reduces erosion and fertilizes the soil, so these advantages would also be lost. The reduction in the number of grazing ruminants would also mean the abandonment of rural areas and an increase in the Spain emptied, as well as a increase in forest fires.
On the other hand, wild ruminants also produce methane and a hypothetical reduction in their population could cause important changes in ecosystems. This strategy was put into practice a few years ago in Australia, where a decade ago the slaughter of thousands of wild camels it was justified, among other reasons, by the need to reduce methane emissions.
Nor can it be forgotten that in developing countries the survival of many families depends on livestock, especially ruminants. In addition, reducing the ruminant population, and with it the production of meat and milk, would bring about an increase in the price of these products, increasing social inequalities.
6. Reduction of meat and milk consumption
The actual effectiveness of this measure is questionable. In some studies, only the reduction obtained has been considered, without taking into account the increase in emissions caused by the production of foods that would replace meat and milk in the diet.
On a study conducted in the United States In which all dietary changes were taken into account, it was estimated that the total elimination of animal protein in the entire American population would only reduce GHG emissions by 2.6% and lead to diets deficient in several essential nutrients and with excess energy.
Another recent study indicates that improving the productive efficiency of livestock would be more effective in reducing methane emissions than reducing the consumption of animal products. Although this type of study is based on predictive models, the disparity in the results obtained in different works reveals the complexity of the subject, as it has even been recognized by the IPCC.
Another important aspect is that the diets of ruminants and other domestic animals usually contain significant amounts of by-products from the agri-food industry (juices and canned vegetables, sugar, breweries, flour mills, distilleries, etc.), which are thus recycled and its possible environmental risk is eliminated. The contribution of livestock to reducing emissions from these industries is often not taken into account when talking about pollution caused by livestock farms.
Towards more efficient livestock production
In summary, while it is true that ruminants contribute significantly to global methane emissions, the many positive aspects of their production must also be considered. Currently there are several strategies that, properly combined, can increase production efficiency and reduce these emissions.
The final objective must be to achieve a more efficient livestock production, which guarantees animal health and well-being and the conservation of natural resources, with economically and socially viable farms that can produce safe food of high nutritional quality.
It is important to note that the Spanish livestock sector makes a continuous effort to reduce polluting emissions and that the improvements made in genetic selection, feeding and manure management in recent years have already have made it possible to considerably reduce the amount of methane generated per kilogram of animal product obtained. There is no doubt that the sector will continue to improve to contribute to the agreed reduction in methane emissions.
This article is part of the coverage of The Conversation on COP26, the Glasgow climate conference.