Cows etc get the nutrients from plants. For a start I am not sure how many vegans can actually process hard plant matter as we are not ruminants. Maybe if they ferment said vegetable matter in big vats they could make use of it. But then the methane and co2 produced would at the end of the day equate to that produced by animals. After all physics and chemistry obey laws not opinions or whims.
The animal after all is a biological factory carrying out chemical processes.
Turning raw materials into other products still uses energy and has biproducts.
You won't have animals in ace you'll need masses of factories in their place to process plant matter.
The vegan milk article recently had me chuckling, not sure how much almonds rice or soy we grow in the uk? But it's okay ignore the transport costs, what's wrong with water we get plenty of that locally.
