"Combining isotopic evidence from ground surface measurements with the newly calculated fire emissions, the team showed that about 17 teragrams per year of the increase is due to fossil fuels, another 12 is from wetlands or rice farming, while fires are decreasing by about 4 teragrams per year. The three numbers combine to 25 teragrams a year -- the same as the observed increase"[1]

The 'cows farting' story is not a major methane source.

https://www.nasa.gov/feature/jpl/nasa-led-study-solves-a-met...

What you're citing here is numbers for previously unexplained emissions, not total emissions.

I.e. there was major uncertainty that scientists were measuring more methane than they expected, and these scientists tried to figure out where it comes from.

The only thing your argument says is that for methane emissions from meat production apparently scientists had a pretty good idea about the numbers.

I don't have a source at hand, so grain of salt and all that... I read somewhere that grass-fed cows also produce a lot less methane than corn-fed cows.

Better dial down on the fiber intake, then!

And have regular blood tests and take your vitamins to keep your biochemistry at the right state.