Let's do the math, shall we: A Land Rover (not a high end engine/trim) will have an emissions level of about 260-300 g/km of CO2. If we're talking about 50 km, that's 13-15 kg/day. Methane weighs 0.717 kg/m³. If we give the cow 200 liters, that's ~143 g/day. Now, some claim that methane may be 20 times more potent than carbon dioxide as a greenhouse gas, thus one cow is equal to a Land Rover driving 9.5 km/day.So it's true, but it's untrue? You were telling the truth just off by a factor of 365? That's all!
Kill all cows!