Let's not forget that grass is what they have evolved to eat. The fact that we can get away with feeding them food that is 10x more calorie dense does not make

Let's not forget that grass is what they have evolved to eat. The fact that we can get away with feeding them food that is 10x more calorie dense does not make that approach correct. As others have said, the most environmentally friendly solution is to drastically reduce consumption of animals, regardless of what we feed them.