Look you can be vegan or whatever if you want, but I think I'll take the risk and eat my juicy barbecued steak. As for the methane : it contribute only roughly 25% of the warming that CO2 does. The reason are simple : the half life of methane in the atmosphere is short and the quantity of methane are 1/200 of those of CO2. And then enteric fermentation is barely above 16% of total methane emission (all farm animals counted, not only cows). Coal mining , oil drilling and treatment is above that , about 19%. Then there are other sources, rice cultivation (12%), waste treatment and landfill (12%), burning of biomass (9%) look up wiki if you wish for more details and more importantly : the sources of citations. Sure we should keep in check, as long as we don't concentrate on "cow" and follow other venue , like reducing coal and oil CO2/Methane emissions.