Doubtful number unless it is as a percentage of bovids.

Some theories say that the Indian culture evolved to dis-favor beef because cow manure is helpful for agriculture.  I kind of doubt that because they burn the stuff without inducing the wrath of whatever-gods-they-have.  OTOH, when people are starved for energy they will burn fuckin' near anything which will burn.  This rather obvious observation undercut's the idea that somehow cutting fossil fuel consumption rates to 1800's levels (per-capita) is going to have some sort of a positive impact on the environment.  On the contrary it is an almost sure-fire (no pun intended) way to ensure nearly complete denudation of most plant life.  Killing most humans makes a lot more sense but most greenies not willing and/or able to think for themselves.  Their leaderships OTOH...

As for methane, my understanding is that at least a significant fraction of it comes from termites which are comparable in biomass and similar in that the host microorganisms which are actually responsible for converting cellulose into methane.

Let's also not forget that methane, although a 'potent greenhouse gas', is not a big cause for concern in the atmosphere because water vapor will absorb electromagnetic radiation on it's spectrum of interest anyway.  This is kind of like the principle that if one is already behind an armor plate, putting up some bullet-proof glass in front of it has little effect.  See:  http://wattsupwiththat.com/2014/04/11/methane-the-irrelevant-greenhouse-gas/