Enteric fermentation is a digestive process by which carbohydrates are broken down by microorganisms into simple molecules for absorption into the bloodstream of an animal. Because of human agricultural reliance in many parts of the world on animals which digest by enteric fermentation, it is the second largest anthropogenic factor for the increase in methane emissions directly after fossil fuel use.
Ruminant animals are those that have a rumen. A rumen is a multichambered stomach found almost exclusively among some artiodactyl mammals, such as cattle, sheep, and deer, enabling them to eat cellulose-enhanced tough plants and grains that monogastric (i.e., "single-chambered stomached") animals, such as humans, dogs, and cats, cannot digest. Although camels are thought to be ruminants they are not true ruminants. [1]
Enteric fermentation occurs when methane (CH4) is produced in the rumen as microbial fermentation takes place. Over 200 species of microorganisms are present in the rumen, although only about 10% of these play an important role in digestion. Most of the CH4 byproduct is belched by the animal. However, a small percentage of CH4 is also produced in the large intestine and passed out as flatulence.
Methane emissions are an important contribution to global greenhouse gas emissions. The IPCC reports that methane is more than twenty times as effective as CO2 at trapping heat in the atmosphere - though note that it is produced in substantially smaller amounts. Methane represents also a significant energy loss to the animal ranging from 2 to 12% of gross energy intake. [2] So, decreasing the production of enteric CH4 from ruminants without altering animal production is desirable both as a strategy to reduce global greenhouse gas emissions and as a means of improving feed conversion efficiency. [3] In Australia ruminant animals account for over half of their green house gas contribution from methane. [4]
However, in Australia there are ruminant species of the kangaroos that are able to produce 80% less methane than cows. This is because the gut microbiota of Macropodids, rumen and others parts of their digestive system, is dominated by bacteria of the family Succinivibrionaceae. These bacteria are able to produce succinate as a final product of the lignocelluloses degradation, producing small amounts of methane as end product. Its special metabolic route allows it to utilize other proton acceptors, avoiding the formation of methane. [5]
Enteric fermentation was the second largest anthropogenic source of methane emissions in the United States from 2000 through 2009. [6] In 2007, methane emissions from enteric fermentation were 2.3% of net greenhouse gases produced in the United States at 139 teragrams of carbon dioxide equivalents (Tg CO2) out of a total net emission of 6087.5 Tg CO2. [7] For this reason, scientists believe that, with the aid of microbial engineering, the use of microbioma to modify natural or anthropogenic processes, we could change the microbiota composition of the rumen of strong methane producers, emulating the Macropodidae microbiota.
Recent studies claim that this technique is possible to perform. In one of these studies scientists analyze the changes of human microbiota by different alimentary changes. [8] In other study, researchers introduce a human microbiota in gnotobiotic mice in order to compare the different changes for developing new ways to manipulate the properties of the microbiota so as to prevent or treat various diseases. [9]
Another approach to manage methane emissions from enteric fermentation involves using diet additives and supplements in cattle feed. [10] For example, Asparagopsis taxiformis (also known as red seaweed) is a species of algae that when fed to cattle has shown to substantially reduce their methane emissions. [11] [12] A second example that has been shown to reduce methane emissions from cattle significantly involves using the compound 3-nitroxypropanol (3-NOP) which inhibits the final step of methane synthesis by microorganisms in the rumen. [13] Some of these methods have already been approved for farmer usage, [14] while others continue to be evaluated for safety, efficacy, and other concerns. [15]
Ruminants are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The process, which takes place in the front part of the digestive system and therefore is called foregut fermentation, typically requires the fermented ingesta to be regurgitated and chewed again. The process of rechewing the cud to further break down plant matter and stimulate digestion is called rumination. The word "ruminant" comes from the Latin ruminare, which means "to chew over again".
Methanogenesis or biomethanation is the formation of methane coupled to energy conservation by microbes known as methanogens. Organisms capable of producing methane for energy conservation have been identified only from the domain Archaea, a group phylogenetically distinct from both eukaryotes and bacteria, although many live in close association with anaerobic bacteria. The production of methane is an important and widespread form of microbial metabolism. In anoxic environments, it is the final step in the decomposition of biomass. Methanogenesis is responsible for significant amounts of natural gas accumulations, the remainder being thermogenic.
Burping is the release of gas from the upper digestive tract of animals through the mouth. It is usually audible.
Gnotobiosis refers to an engineered state of an organism in which all forms of life in or on it, including its microbiota, have been identified. The term gnotobiotic organism, or gnotobiote, can refer to a model organism that is colonized with a specific community of known microorganisms or that contains no microorganisms (germ-free) often for experimental purposes. The study of gnotobiosis and the generation of various types of gnotobiotic model organisms as tools for studying interactions between host organisms and microorganisms is referred to as gnotobiology.
The hydrogen cycle consists of hydrogen exchanges between biotic (living) and abiotic (non-living) sources and sinks of hydrogen-containing compounds.
The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment allows it to serve as the primary site for microbial fermentation of ingested feed. The smaller part of the reticulorumen is the reticulum, which is fully continuous with the rumen, but differs from it with regard to the texture of its lining.
Livestock's Long Shadow: Environmental Issues and Options is a United Nations report, released by the Food and Agriculture Organization (FAO) of the United Nations on 29 November 2006, that "aims to assess the full impact of the livestock sector on environmental problems, along with potential technical and policy approaches to mitigation". It stated that livestock accounts for 18% of anthropogenic greenhouse gas emissions, a figure which FAO changed to 14.5% in its 2013 study Tackling climate change through livestock.
A low-carbon diet is any diet that results in lower greenhouse gas emissions. Choosing a low carbon diet is one facet of developing sustainable diets which increase the long-term sustainability of humanity.
The environmental impacts of animal agriculture vary because of the wide variety of agricultural practices employed around the world. Despite this, all agricultural practices have been found to have a variety of effects on the environment to some extent. Animal agriculture, in particular meat production, can cause pollution, greenhouse gas emissions, biodiversity loss, disease, and significant consumption of land, food, and water. Meat is obtained through a variety of methods, including organic farming, free-range farming, intensive livestock production, and subsistence agriculture. The livestock sector also includes wool, egg and dairy production, the livestock used for tillage, and fish farming.
Methane is a chemical compound with the chemical formula CH4. It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Earth makes it an economically attractive fuel, although capturing and storing it poses technical challenges due to its gaseous state under normal conditions for temperature and pressure.
Asparagopsis armata is a species of marine red algae, in the family Bonnemaisoniaceae. English name(s) include red harpoon weed. They are multicellular eukaryotic organisms. This species was first described in 1855 by Harvey, an Irish botanist who found the algae on the Western Australian coast. A. armata usually develops on infralittoral rocky bottoms around the seawater surface to around 40m of depth. Marine algae like A. armata are considered "autogenic ecosystem engineers" as they are at the very bottom of the food chain and control resource availability to other organisms in the ecosystem.
Atmospheric methane is the methane present in Earth's atmosphere. The concentration of atmospheric methane is increasing due to methane emissions, and is causing climate change. Methane is one of the most potent greenhouse gases. Methane's radiative forcing (RF) of climate is direct, and it is the second largest contributor to human-caused climate forcing in the historical period. Methane is a major source of water vapour in the stratosphere through oxidation; and water vapour adds about 15% to methane's radiative forcing effect. The global warming potential (GWP) for methane is about 84 in terms of its impact over a 20-year timeframe. That means it traps 84 times more heat per mass unit than carbon dioxide (CO2) and 105 times the effect when accounting for aerosol interactions.
Asparagopsis taxiformis, formerly A. sanfordiana, is a species of red algae, with cosmopolitan distribution in tropical to warm temperate waters. Researchers have demonstrated that feeding ruminants a diet containing 0.2% A. taxiformis seaweed reduced their methane emissions by nearly 99 percent.
Greenhouse gas emissions from wetlands of concern consist primarily of methane and nitrous oxide emissions. Wetlands are the largest natural source of atmospheric methane in the world, and are therefore a major area of concern with respect to climate change. Wetlands account for approximately 20 - 30% of atmospheric methane through emissions from soils and plants, and contribute an approximate average of 161 Tg of methane to the atmosphere per year.
Asparagopsis is a genus of edible red macroalgae (Rhodophyta). The species Asparagopsis taxiformis is found throughout the tropical and subtropical regions, while Asparagopsis armata is found in warm temperate regions. Both species are highly invasive, and have colonised the Mediterranean Sea. A third accepted species is A. svedelii, while others are of uncertain status.
Karen Beauchemin is a federal scientist in Canada who is recognized as an international authority on methane emissions and ruminant nutrition. Her research helps develop farming techniques that improve how we raise cattle for meat and milk, while reducing the environmental impacts of livestock production.
Increasing methane emissions are a major contributor to the rising concentration of greenhouse gases in Earth's atmosphere, and are responsible for up to one-third of near-term global heating. During 2019, about 60% of methane released globally was from human activities, while natural sources contributed about 40%. Reducing methane emissions by capturing and utilizing the gas can produce simultaneous environmental and economic benefits.
FutureFeed is a seaweed-based feed ingredient for livestock that is currently being developed by a team from Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). The primary component of FutureFeed is dried Asparagopsis, a genus of red algae, which has been shown to reduce the methane (CH4) emissions of ruminant livestock by up to 99%. It is added to fodder at feedlots in dosages of 1-2% dietary intake to achieve this result. FutureFeed is currently being developed in collaboration with James Cook University (JCU) and Meat and Livestock Australia (MLA), with the primary goal of scaling for mainstream commercial use.
The amount of greenhouse gas emissions from agriculture is significant: The agriculture, forestry and land use sector contribute between 13% and 21% of global greenhouse gas emissions. Agriculture contributes towards climate change through direct greenhouse gas emissions and by the conversion of non-agricultural land such as forests into agricultural land. Emissions of nitrous oxide and methane make up over half of total greenhouse gas emission from agriculture. Animal husbandry is a major source of greenhouse gas emissions.
Anaeromyces robustus is a fungal microorganism that lives in the gut rumen of many ruminant herbivores such as cows and sheep. Previously thought to be protozoa from their flagellated zoospores, they are biomass degraders and help the animal by breaking down carbohydrates and plant materials from the food the animal ingests. This fungus, therefore, is anaerobic and lives without oxygen. Gut fungi are dramatically outnumbered by other organisms in the microbiome; however, they are important members of the gut microbiome in ruminants and hind-gut fermenters and play a key role in digestion.