What fraction of natural gas consumption could the US obtain by composting cattle manure?

Question

The US cattle herd was 95,497,994 in 2002

http://www.nass.usda.gov/census/census02/volume1/us/st99_1_014_016.pdf

US natural gas consumption in 2006 was 21,653 billion cubic feet

http://www.eia.doe.gov/basics/energybasics101.html

Bangladesh has 20,000 cattle manure composters built with materials costing less than $2000 each. How many composters does the US have?

Answer 1

It would be less than the energy that could be obtained by burning the grass *before* it goes through a cow.

Answer 2

about 1 to 7 percent.

Answer 3

in Bangladesh, a composter is likely to be a half of a large drum, immersed in a vat of water, in which dung is dumped in the side, and the resulting methane is caught in the drum and used for cooking.

i think this is not likely to catch on in a large way around the more dainty US.

as to the US cows, i'd guess that less than half are contained in feed lots where the manure could be composted.

add to that i don't know how much methane is produced, and the answer is not at all obvious.

then there's the method to consider.

how will it be done?

not trying to rain on your parade, but there are a considerable number of questions here.