Livestock matters because it is the biggest land user in the world. More land is given over to grazing animals than for any other single purpose. About a third of the world’s crops are fed to animals, and they use a third of all available fresh water. Something like 1.3 billion people depend in some way on raising animals; animals provide a third of the protein in peoples’ diets and the business accounts for a third of global agricultural GDP. But meat is an inefficient source of calories. It accounts for 17% of global calorific intake, but uses twice that amount of land, water and feed.

So the question is, what sort of livestock farming can satisfy the growing appetites, while using land, water and food crops more rationally? 

Livestock: Meat and greens | The Economist.