Methane is produced as part of normal digestive processes in animals. During digestion, microbes present in an animal’s digestive system ferment food consumed by the animal. This microbial fermentation process, referred to as enteric fermentation, produces methane as a byproduct, which can be exhaled or eructated (farted) by the animal. The amount of methane produced and emitted by an individual animal depends primarily upon the animal's digestive system, and the amount and type of feed it consumes.
Ruminant animals like cows are major emitters of methane because of their unique digestive system. Ruminants possess a rumen, or large "fore-stomach," in which microbial fermentation breaks down the feed they consume into products that can be absorbed and metabolized. The microbial fermentation that occurs in the rumen enables them to digest coarse plant material that non-ruminant animals cannot. Ruminant animals, consequently, have the highest methane emissions among all animal types; reportedly emitting 22% of the nation’s methane gas releases . In addition to the type of digestive system, an animal’s feed quality and feed intake also affects methane emissions.
The methane output of Vermont cows dropped 18% while milk production remained stable during feeding experiments. The cows had their grain feed adjusted to include more plants like alfalfa and flaxseed and less corn. This feed is more like the natural grasses that the cows evolved eating. In addition to producing less methane, the cows were observed to be healthier. This study evolved out of research performed by the makers of Danon yogurt in France. Scientists working with Groupe Danone had been studying why their cows were healthier and produced more milk in the spring. The answer, the scientists determined, was that spring grasses are high in Omega-3 fatty acids, which may help the cow’s digestive tract operate smoothly.
Corn and soy, the feed that became dominant feed in the agro-industrial dairy industry, has a completely different type of fatty acid structure. The French sturdy found a reduction in methane release of about 30% at 600 farms. The difference from the Vermont experience was attributed to the fact that the Vermont animals were already pastured and received some of their food from grasses.
This brings up a proven way to reduce some methane emissions is to get dairy cows (and beef cows) out of their stalls and into the pasture. This allows the manure to decompose naturally and spew less methane into the atmosphere. Pasture raised, grass feed cows produce less methane. This practice, though, is criticized as time-consuming and land-intensive. It is certainly much more humane.
Methane digesters, can be used in operations where the cows are in stalls. The cow manure is washed into airtight chambers where the waste breaks down and releases methane gas for power or fuel, cost several hundred thousand dollars and require considerable upkeep. These are simply waste water treatment systems. The dairy industry claims the many of the digesters in California have stopped working. These systems cost several hundred thousand dollars and emit other pollutants like nitrogen oxide and particulate matter- which are a health hazard and are regulated under the new particulate standards. California has problems in several areas complying with the particulate standards. The real goal of the regulation was suggested in an article published in The Lancet.
In their 2007 article “Food, livestock production, energy, climate change, and health,” by Anthony J McMichael, John W Powles, Colin D Butler, Ricardo Uauy; the authors present research that available technologies for reduction of emissions from livestock production, applied universally at realistic costs, would reduce non-carbon dioxide emissions by less than 20%. The authors go on to state because rapid reductions in greenhouse-gas emissions per unit of livestock production would be technically and culturally diﬃcult in the short term, the prime objective must be to reduce consumption of animal products in high-income countries. “We therefore advocate a contraction and convergence strategy to reduce consumption of livestock products... Contraction of consumption in high-income countries per head would then deﬁne the lower, common, ceiling to which low-income and middle-income countries could also converge.”