A report just out by Lord Stern has revealed the true extent of animal consumption and production, even 'free range ethical' meat. This has of course been documented many times in the past.
I thought cow-belching, rather than cow-farting, was the main problem. And a cow trained to chew plenty of garlic, even as a condiment to her regular grazing, apparently reduces her methane output.
I'm working on it - but meanwhile it seems there are herds of big western-style cows on Mars.
Imperial College scientists have ruled out methane bearing meteorites as there's just too much of the stuff there. They're guessing it's down to volcanoes or microbes on the planet. But with evidence of 100 - 300 tons of it, I think it must be big fat milch Friesians or some of the French breeds.