Research is underway to process grass into a milk-substitute. It's a matter of making microorganisms that create the right mix of proteins from ground grass. Plenty of food is already created this way. E.g. microbial rennet is made up from proteolytic enzymes grown in a fermentor and natural (as opposed to chemical) vanillin can be made by a microbe.
Not necessarily - I don't know about where you're from, but here our cows and sheep eat grass and live in fields that wouldn't be suitable for crops