(Originally published May 27, 2016 on Examiner.com).
With ruminants (cattle, sheep, goats, bison, buffalo, deer, elk, antelope, etc), most methane is produced via enteric fermentation. Enteric fermentation is belching (not “farts”). For enteric fermentation, ruminants have bacteria in their rumen called methanogens that break down what ruminants eat (grasses) via a process called methanogenesis. This process is similar to anaerobic composting so essentially ruminants are composters. They eat grasses and poop manure which is composted material. This capacity to function as composters is incredibly invaluable in dryer environments where there isn’t much humidity for organic matter outside a ruminant’s rumen to decompose. Decomposition, in general, needs moisture. With ruminants some methane is emitted via their manure in pasture , but again the vast majority comes from belching (enteric fermentation).
But here’s the fascinating thing about mother nature, there’s balance. In intact ecosystems (especially grasslands) healthy soils have microbes called methanotrophs to oxidize the atmospheric enteric methane belched by the ruminants. The effectiveness of these methanotrophs is debated and needs further research, but vast herds of wild ruminants existed for thousands of years without causing significant increases in atmospheric spikes of methane levels. Here’s a prior LA Chef’s column article on this topic: LA Chefs Editorial – methane and global warming. In this article there are scientific references detailing these processes.
These vast herds also built soils and soil fertility in many regions of the world. Those soils also sequestered carbon. Removing the wild ruminants (killing all the large herds of bison and elk) and their apex predators eliminated the portion of the ecosystem that built this fertile soil that sequesters carbon. Well managed domesticated cattle can bio-mimic wild ruminant movements and thus also build soil. Note too that over tillage, as well as chemically intensive modern industrial agriculture practices, has released a lot of sequestered carbon into the atmosphere and or undermined the soil microbial activity that makes these processes possible including methane oxidation. Thus tilled and pesticide treated cropland doesn’t as effectively function as a methane sink as grasslands. Additionally, grasslands sequester as much carbon as tropical forests (click hyperlink to see chart ).Wetlands sequester the most, but wetlands also emit the most methane. Tropical forests emit a lot of methane as well. Trees in rain forests actually are the largest emitters in their ecosystem. So with any ecosystem, one has to look at the system as a whole, and not simply reduce that ecosystem to its parts as so many are wont to do. All the parts of any ecosystem include the animals living in that ecosystem.
The other major way livestock produce methane is through manure management largely from concentrated indoor (CAFO’s – pigs and chickens) and outdoor operations (feedlots- cattle). Because livestock are all brought to one spot all their manure has to be managed. This manure held in manure lagoons off gases methane as the manure decomposes. The manure is too expensive to truck away, so in its liquefied state it is spread onto nearby fields as a slurry which is way more than the land can handle. Thus here too the manure off gases methane into the atmosphere. Manure management isn’t as significant an issue on non-concentrated pastured based small farms, since the land can accommodate the amount of manure littered onto it by the livestock. Such manure is actually essential to rebuild soils and soil fertility. Click this link to hear a great talk by Gabe Brown on building healthy soils. This rebuilt soil provides the carbon benefits noted above. Cattle finished in feedlots don’t provide any soil building or carbon sequestration benefits. Sadly concentrated operations take livestock’s biggest asset manure, a fertilizer, and often turn this asset into a toxic substance laced with drugs.