Cos more methane from mouth or dung?

March 7, 2008 10:22 AM

Is it possible to say whether more methane is produced from cow feces or their mouths? How political is this topic?

I thought I read in the NY Times about some studies in Australia/NZ that methane emission from cow dung may not be nearly as significant as the methane released from their mouths. I mentioned this to someone trying to harness the methane from fecal lagoons for energy and it has started a bit of a jovial debate. Apparently my friend spoke to the cow caca methane guru and is gleefully waiting to send some proof that this is not true (the guru apparently also had not nice words to say about "people like me"). Harumph to him too. Well, people like me can be hard-headed so now I am curious. I know these issues can be deeply politicized and statistics work wonders in all kinds of ways so what's the scoop on methane from poop versus mouth? Any good respected, neutral info/studies/reports out there you can point me to?

Thanks!

posted by beelover to science & nature (16 comments total)

I actually attended a lecture on this topic this week with Ryan Kennedy. The link is a good start to the issue, printed in Alternatives Journal, an academic publication.
posted by carabiner at 10:32 AM on March 7, 2008

There are a number of installations in Vermont, generating significant amounts of power, running on methane from cow manure. So, there's a lot of methane in the manure, ie., it is certainly "significant".

It certainly could be that they belch even more methane, but you could not capture it very easily to turn it into energy.
posted by beagle at 10:33 AM on March 7, 2008

Vermont installations link.
posted by beagle at 10:34 AM on March 7, 2008

In this Digg comment, the guy says eructations (belches) are a bigger problem than flatulence, but he's not considering dung. (And he has a financial interest.) You might try skimming through this report.
posted by salvia at 10:34 AM on March 7, 2008

Trying again: Vermont cow power link.
posted by beagle at 10:53 AM on March 7, 2008

What would also be useful to know is the difference between grass fed and grain fed animals. If there is a difference.
posted by Toekneesan at 10:53 AM on March 7, 2008

Cows that are fed grain tend to suffer from indigestion since grain is not normally a part of a cow's diet; I would imagine cows that are grass-fed don't have as much a problem with indigestion, and therefore, produce less methane than their grain-eating counterparts.
posted by chan.caro at 11:09 AM on March 7, 2008

From the Globe and Mail's Social Studies, June 12, 2003:

Methane burps. In the past century, the amount of methane -- the second-most important greenhouse gas -- has more than doubled in the atmosphere. Cattle account for about 20 per cent, the Los Angeles Times says. "The key to understanding the problem is knowing which end of the cow is responsible. About 95 per cent of the gas originates, not as flatulence, but as exhalation." A single cow can exhale as much as 634 quarts of methane a day. Worldwide, that translates to nearly 100 million tons of the gas annually.


Excerpts from the original article from the LA Times, which explains why cattle produce methane:

COLUMN ONE; Getting the Cows to Cool It; Cattle are a prodigious source of methane, a major contributor to global warming. Scientists are at work on some remedies.
Gary Polakovic
Times Staff Writer
1711 words
7 June 2003
Los Angeles Times
Home Edition
A-1
English
Copyright 2003 The Los Angeles Times

...

Like cows the world over, Lucy is a prodigious source of methane, a major constituent of greenhouse gases. Chewing away, she is a picture of benign passivity. But the inner Lucy is a fermentation factory. The more she chews, the more she belches molecules of methane that float into the sky and trap the sun's heat.

...

The world's cattle herds number about 1.3 billion animals -- more than double the number 30 years ago. There are also 1.1 billion sheep and goats. In the United States, cattle have become so numerous that there are two animals for every five people. California and Texas have the most dairy and beef cattle. The Environmental Protection Agency estimates that 25% of the nation's methane emissions come from livestock.

In eastern Washington, Scotland, New Zealand and Australia, feedlots and pastures are becoming laboratories for researchers testing an assortment of potential remedies for livestock greenhouse gas. They are experimenting with vaccines, reformulated feed, selective breeding and bioengineered cows.

...


The key to understanding the problem is knowing which end of the cow is responsible. About 95% of the gas originates, not as flatulence, but as exhalation. It is the unwanted byproduct of a unique digestive system that has made cattle engines of agricultural production, but also prodigious belchers.

Cows lived in harmony with the atmosphere for thousands of years. Then humans developed a taste for the animals and their dairy products, and nature's equilibrium was disturbed. Simple barnyard creatures were transformed into agents of climate change, not by their own doing, but because people dramatically multiplied their numbers so they would produce more milk, cheese and meat.

Methane comes from a variety of sources, including coal mining, rice paddies and wetlands. Human activities produce about two-thirds of the gas. Methane accounts for about 20% of planetary warming, studies show.

...

A single cow can exhale as much as 634 quarts of methane per day. Worldwide, that translates to nearly 100 million tons of methane annually.

Cows belong to a class of animals known as ruminants, which also includes sheep, goats, camels and buffaloes. Each animal has a four-chambered stomach, including a large forestomach called the rumen, where the hard work of digestion takes place.

The rumen allows the animals to consume coarse, fibrous vegetation. This makes them easy to raise because they can find nourishment in a variety of environments. It is one reason they were domesticated in the first place.

The drawback is that the animals have chronic indigestion. A cow swallows its meal to the rumen -- only to regurgitate it and chew it again. They do this over and over, which is why cows always seem to be munching.

With each chewing cycle, the cow's food is immersed in a broth of fungi, protozoa and bacteria inside the 42-gallon rumen. One particular bacterium feeds on hydrogen and produces methane as a waste product. When the cow spits up its cud, out comes the methane in a process called "enteric fermentation."

"It's the prima donna of the fermenters," said Don Johnson, professor of animal nutrition at Colorado State University. "It has the best system for digestion of plant material."

...

"It's a natural process that a ruminant animal goes through," said Chandler Keys, vice president of government affairs for the National Cattlemen's Beef Assn. "There's not much you can do about it. If you want to control methane emissions in the world, controlling it from cows has to be pretty low on the totem pole."

But controlling it would be good for agriculture's bottom line as well as for the environment. About 6% of the food a cow eats -- a single dairy cow consumes about 50 pounds of feed daily -- is lost as methane.

"There are plenty of reasons to keep the cows from giving off methane. It makes more sense to have it as weight on the cattle. If we can succeed, cows produce less methane and have more meat or milk," said Sherwood Rowland, a University of California atmospheric chemist who won a Nobel Prize in 1995 for discovering how man-made chemicals damage the Earth's protective ozone layer.

Adding nitrogen-rich urea to a cow's diet can lower methane exhalations by more than 25%, studies show. U.S. cows typically eat a high-grain diet, which is easier to digest and produces less methane, Johnson said.

Other strategies are more unorthodox, including feeding the animals chlorinated hydrocarbons, commonly found in solvents and gasoline, and altering the chemistry of the rumen to more closely resemble that of a kangaroo.

....

The researchers are testing vaccines that trigger an animal's immune system to battle methane-causing microbes, said Mark Howden, a climate change researcher for the Commonwealth Scientific and Industrial Research Organization in Canberra.

...

In Scotland, scientists at the Rowett Research Institute have identified a bacterium in soil that breaks methane down into hydrogen and carbon dioxide. If they can make it work in cows, it could cut British methane emissions by 6%. Canadian researchers are experimenting with vegetable-oil feed supplements that cut livestock methane by 15%.

...


See also an article on the Scottish efforts referred to in the LA Times article: reducing methane through cows' diet.
posted by Dasein at 11:34 AM on March 7, 2008

Excuse the pun

It has become a politicized issue: the government here tried to impose a 'fart tax' on ruminants as part of an ecological policy and the resulting protests reinforce every pastoral-hick stereotype (that's the former leader of the opposition on the tractor). The point was made then that ows produce much more methane from the mouth than from the other end.
posted by Paragon at 11:41 AM on March 7, 2008

Here's a good listen from a recent Quirks and Quarks podcast: Dr. Athol Klieve, a researcher with the Department of Primary Industries & Fisheries in Queensland, Australia, is studying the gut bacteria of certain species of kangaroo, in the hope that they can be transfered into the digestive system of cattle; and, in doing so, significantly cut back the amount of greenhouse gas they produce. Interview (mp3).
posted by jaimev at 11:56 AM on March 7, 2008

I don't think the question is really answered. We have two newspaper articles saying that 95% of the methane comes from the front end of the cow. Neither story provides a source for that statement, and as we well know, plenty of canards get repeated until they are accepted as truth, when they have no foundation whatever in actual research. ("You need to drink 8 glasses of water a day" for example.)

Besides burps and farts, there's also the methane exuded by the cow dung, as mentioned by the OP. So there are three sources from one cow. The methane that comes from the manure is a product of continued bacterial activity after the manure leaves the cow. This happens, and the methane is released, whether the manure is spread on a field or put into an anearobic composting unit to generate electricity.

So in any event, allow me to restate the question:

Cite a credible scientific study that quantifies the amounts of methane exuded over a period of time by one cow (a) as eructative exhalation, (b) as flatulent emissions, and (c) from the manure produced by cow as it biodegrades through bacterial action.

Extra credit for providing the same information on other ruminants.
posted by beagle at 2:24 PM on March 7, 2008

beagle, instead of complaining about the other answers, why don't you start googling? The report I cited above comes pretty close to answering the question, and that was like the third google result for "methane eructation" or "carbon emissions eructation flatulence" or something like that.
posted by salvia at 3:01 PM on March 7, 2008

...the methane is released, whether the manure is spread on a field or put into an anearobic composting unit...

Not so, and that assumption might be the cause of the whole disagreement. It is possible to get more or less methane from dung depending on how you handle it. "Spread on a field" is pretty much the opposite of "anaerobic composting".
posted by Canard de Vasco at 3:39 PM on March 7, 2008

Salvia: I'm interested in the question, and I've been googling. I'm not complaining about other answers, but I'm saying they don't answer the question posed by the OP, which asks for "proof", and "neutral info/studies/reports. I did "skim" the report you linked to, but if it "comes close", it doesn't answer the question. Neither of the words "eructation" or "flatulence" appear in it, by the way.

Canard de Vasco: I'll stand corrected if anaerobic composting doesn't happen on the meadow, although I've seen my farmer neighbor spread it so thick that only anaerobic processes could be happening down underneath. But if spreading the manure releases less methane, can you cite a study?
posted by beagle at 7:07 PM on March 7, 2008

beagle, are we talking about the same report? Did you click anything? For example, if you click on the methane section, Chapter 7, it contains this sentence:

Murray et al (1976) showed in sheep fed 800 g lucerne chaff per day, that while 87% of methane was produced in the rumen and 13% in the lower digestive tract, >98% was excreted via the mouth and about 2% in the flatus.

It's talking about both the location where the methane was generated, and the location where it was expelled. It goes into emissions from effluent ponds, what difference different feed makes, etc.
posted by salvia at 11:51 PM on March 7, 2008

When I said "spread" I was thinking of the NZ context, where it's actually more like "sprayed", not too deep, and even then only involves the manure dropped during the small part of the day that dairy cows spend in their milking shed. New Zealand's Ministry for the Environment says that in New Zealand enteric fermentation produces around 30 times more CO₂ equivalent emissions than "manure management", but that wouldn't carry across to countries that use feedlots rather than pasture because:

In New Zealand only dairy cows have a fraction (5 percent) of the excreta stored in an anaerobic lagoon waste system. The remaining 95 percent of excreta from dairy cattle is deposited directly on pasture. All other ruminant species (sheep, beef cattle, deer and goats) deposit all faecal material directly onto pastures.

So

I've seen my farmer neighbor spread it so thick that only anaerobic processes could be happening down underneath

In Australia or New Zealand you would never see that.
posted by Canard de Vasco at 12:38 AM on March 8, 2008