THE most comprehensive analysis of greenhouse emissions of livestock and Australian feral and native animals has shown kangaroos to be the most planet-friendly, while emus do considerable climate warming and camels are among the worst offenders.

In the US, animal husbandry contributes 18% of anthropogenic GHG emissions - more than all forms of transport combined.
“Livestock’s Long Shadow” (ftp://ftp.fao.org/docrep/fao/010/a0701e/A0701E00.pdf)

For some reason the main article from the Australian (page 4, Jan 13) is not available online. It has a lot of the interesting comparisons. The wrost offenders (emissions per kg weight) are dairy cattle. Our feral camels emit the equivalent of 300,000 cars - so would be a good target for reducing our emissions.

C02 eqivalent, tonnes per head per year:
dairy cattle 2.39
beef cattle: 1.67
camels: 0.97
emus: 0.11 - on par with goats, not much less than sheep, nearly four times the rate from pigs.

Roos emit acetone instead of methane. Acetone is not a GHG. The author (George Wilson, Ausatralian Wildlife Services) is chamioning a proposal for graziers on rangelands to shift from sheep and cattle to harvesting roos.

How kangaroo burgers could save the planet
http://www.newscientist.com/article/mg20026873.100-how-kangaroo-burgers-could-save-the-planet.html

Animals under fire in methane blame game
http://www.theaustralian.com.au/news/features/animals-under-fire-in-methane-blame-game/story-e6frg6z6-1225818573869

Burp-less sheep to help tackle climate change
http://www.news.com.au/couriermail/story/0,,26595742-5013016,00.html

Meat goes off the menu for young city dwellers
http://www.theaustralian.com.au/business/news/meat-goes-off-the-menu-for-young-city-dwellers/story-e6frg90f-1225792998928

Farmers dispute animal methane measure
http://www.theaustralian.com.au/business/industry-sectors/farmers-dispute-animal-methane-measure/story-e6frg95o-1225782760587
CLAIMS that cattle and sheep are responsible for 10.9 per cent of Australia's greenhouse gas emissions have been called into question after scientists discovered considerable variation in the amount of methane produced by individual animals.

Scientists breeding cows that burp less
http://www.heraldsun.com.au/news/scientists-breeding-cows-that-burp-less/story-0-1225740947226

Milking the eco message
http://www.theaustralian.com.au/news/milking-the-eco-message/story-0-1225733475587

Seaweed a cure for cow greenhouse gas
http://www.news.com.au/couriermail/story/0,,26059777-3102,00.html

an interestin opinion piece criticising the claims that animals contribute to our GHG emissions:
Green House Gas Emissions and Livestock
http://agmates.ning.com/profiles/blogs/green-house-gas-emissions-and

Yeah, but it's a drop in the ocean worldwide. Having said that, Agriculture plus Land-use comes second only to Stationary Energy in Australia, accounting for about 20% of Australia's greenhouse gas inventory.