A 1999 Article in American Society of Animal Science says that "Cattle are responsible for 20 percent of U.S. emissions of methane (CH4), which traps heat in the atmosphere 20 times more effectively than carbon dioxide (CO2)." and Grass fed cattle produce 4 times more methane than grain-fed cattle.
What they don't say is that grain-fed cattle eat mainly corn.
The reason grass-fed cows produce more methane is lignin, a hard-to-digest substance in the plant cell wall. Resistant to ordinary digestion, lignin must be converted to energy with the help of microflora inhabiting a cow's gut. As the microflora degrade the lignin, methane is released.
Grain-feeding is not only unnatural and dangerous for the cows.
In its less-than-infinite wisdom, however, the USDA continues to grade beef in a way that rewards marbling with intra-muscular fat.
From: "barbara conover"
I sent this around to a small group I'm working with to try and create a "Green Restaurant Association" locally (one of our requirements would be to have good vegetarian options on the menu: we have discussed the environmental impacts of eating meat...).
Got these 2 responses which might be educational for those interested in this issue (particularly the "foodrevolution" one... but I like his comment on considering the GHG-impact of the whole process when comparing the two feeds... I'm assuming many saw the horrific grain-fed cattle in Food, Inc. -- if you haven't seen that movie DO SO!!! Requirement for anyone who eats!
Check out the page I saw at:
Another brief article follows below (I sent a different one earlier).
Again, from what I understand, "grain-fed" means corn-fed and that's not good. All cows produce methane, and I understand grass-fed cattle themselves produce more, but the production process of growing and feeding them corn seems to cause much more GHG-gas emissions than grass-fed. And the system of corn-fed cows raised in feedlots causes many other problems, such as over-use of anti-biotics, etc.
Only humans would think of trying to solve the methane-producing problem by developing Genetically modified grass or meat grown in test tubes!
While many cattle are stuffed full of grain, grass-fed cattle have been heralded as a greener way to get beef because it diminishes the need to feed the animals antibiotics and has a smaller carbon footprint, not to mention that it yields beef with less saturated fat. Those of us lucky (or wealthy) enough to feast on grass-fed beef can rest easy knowing we have taken a step toward protecting planet Earth--or so we thought.
It turns out there's a hitch: Cow burps, which send methane into the atmosphere, may increase global warming. Cattle are responsible for 20 percent of U.S. emissions of methane, which traps heat in the atmosphere 20 times more effectively than carbon dioxide.
"Greener" grass-fed cattle are part of this methane problem too. The reason is lignin--a hard-to-digest substance in the plant cell wall. Resistant to ordinary digestion, lignin must be converted to energy with the help of microflora inhabiting a cow's gut. As the microflora degrade the lignin, methane is released. But for those who eat grass-fed beef, there may be a solution.
To take care of a cow's gas problem, the Australian company Gramina has developed genetically modified grass that contains less lignin, making it easier--and more polite--to digest. "Genetically modified grass could be an appealing solution," says Carnegie Mellon engineer Christopher Weber, who recently released a report on issues surrounding beef's contribution to greenhouse gases. It could be more acceptable to the carnivores among us, he adds, "than meat grown in test tubes or giving up meat altogether."